/*
* Copyright (C) Mellanox Technologies Ltd. 2001-2014.  ALL RIGHTS RESERVED.
* Copyright (C) UT-Battelle, LLC. 2014-2017. ALL RIGHTS RESERVED.
* Copyright (C) ARM Ltd. 2016-2017.  ALL RIGHTS RESERVED.
* Copyright (C) Los Alamos National Security, LLC. 2018 ALL RIGHTS RESERVED.
* See file LICENSE for terms.
*/

#ifndef UCP_H_
#define UCP_H_

#include <ucp/api/ucp_def.h>
#include <ucp/api/ucp_compat.h>
#include <ucp/api/ucp_version.h>
#include <ucs/type/thread_mode.h>
#include <ucs/type/cpu_set.h>
#include <ucs/config/types.h>
#include <ucs/sys/compiler_def.h>
#include <ucs/memory/memory_type.h>
#include <stdio.h>
#include <sys/types.h>

BEGIN_C_DECLS

/**
 * @defgroup UCP_API Unified Communication Protocol (UCP) API
 * @{
 * This section describes UCP API.
 * @}
 */

/**
 * @defgroup UCP_CONTEXT UCP Application Context
 * @ingroup UCP_API
 * @{
 * Application  context is a primary concept of UCP design which
 * provides an isolation mechanism, allowing resources associated
 * with the context to separate or share network communication context
 * across multiple instances of applications.
 *
 * This section provides a detailed description of this concept and
 * routines associated with it.
 *
 * @}
 */


 /**
 * @defgroup UCP_WORKER UCP Worker
 * @ingroup UCP_API
 * @{
 * UCP Worker routines
 * @}
 */


 /**
 * @defgroup UCP_MEM UCP Memory routines
 * @ingroup UCP_API
 * @{
 * UCP Memory routines
 * @}
 */


 /**
 * @defgroup UCP_WAKEUP UCP Wake-up routines
 * @ingroup UCP_API
 * @{
 * UCP Wake-up routines
 * @}
 */


 /**
 * @defgroup UCP_ENDPOINT UCP Endpoint
 * @ingroup UCP_API
 * @{
 * UCP Endpoint routines
 * @}
 */


 /**
 * @defgroup UCP_COMM UCP Communication routines
 * @ingroup UCP_API
 * @{
 * UCP Communication routines
 * @}
 */


 /**
 * @defgroup UCP_CONFIG UCP Configuration
 * @ingroup UCP_API
 * @{
 * This section describes routines for configuration
 * of the UCP network layer
 * @}
 */


 /**
 * @defgroup UCP_DATATYPE UCP Data type routines
 * @ingroup UCP_API
 * @{
 * UCP Data type routines
 * @}
 */


/**
 * @ingroup UCP_CONTEXT
 * @brief UCP context parameters field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_params_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_params_field {
    UCP_PARAM_FIELD_FEATURES          = UCS_BIT(0), /**< features */
    UCP_PARAM_FIELD_REQUEST_SIZE      = UCS_BIT(1), /**< request_size */
    UCP_PARAM_FIELD_REQUEST_INIT      = UCS_BIT(2), /**< request_init */
    UCP_PARAM_FIELD_REQUEST_CLEANUP   = UCS_BIT(3), /**< request_cleanup */
    UCP_PARAM_FIELD_TAG_SENDER_MASK   = UCS_BIT(4), /**< tag_sender_mask */
    UCP_PARAM_FIELD_MT_WORKERS_SHARED = UCS_BIT(5), /**< mt_workers_shared */
    UCP_PARAM_FIELD_ESTIMATED_NUM_EPS = UCS_BIT(6), /**< estimated_num_eps */
    UCP_PARAM_FIELD_ESTIMATED_NUM_PPN = UCS_BIT(7)  /**< estimated_num_ppn */
};


/**
 * @ingroup UCP_CONTEXT
 * @brief UCP configuration features
 *
 * The enumeration list describes the features supported by UCP.  An
 * application can request the features using @ref ucp_params_t "UCP parameters"
 * during @ref ucp_init "UCP initialization" process.
 */
enum ucp_feature {
    UCP_FEATURE_TAG          = UCS_BIT(0),  /**< Request tag matching
                                                 support */
    UCP_FEATURE_RMA          = UCS_BIT(1),  /**< Request remote memory
                                                 access support */
    UCP_FEATURE_AMO32        = UCS_BIT(2),  /**< Request 32-bit atomic
                                                 operations support */
    UCP_FEATURE_AMO64        = UCS_BIT(3),  /**< Request 64-bit atomic
                                                 operations support */
    UCP_FEATURE_WAKEUP       = UCS_BIT(4),  /**< Request interrupt
                                                 notification support */
    UCP_FEATURE_STREAM       = UCS_BIT(5),  /**< Request stream support */
    UCP_FEATURE_AM           = UCS_BIT(6)   /**< Request Active Message
                                                 support */
};


/**
 * @ingroup UCP_WORKER
 * @brief UCP worker parameters field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_worker_params_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_worker_params_field {
    UCP_WORKER_PARAM_FIELD_THREAD_MODE  = UCS_BIT(0), /**< UCP thread mode */
    UCP_WORKER_PARAM_FIELD_CPU_MASK     = UCS_BIT(1), /**< Worker's CPU bitmap */
    UCP_WORKER_PARAM_FIELD_EVENTS       = UCS_BIT(2), /**< Worker's events bitmap */
    UCP_WORKER_PARAM_FIELD_USER_DATA    = UCS_BIT(3), /**< User data */
    UCP_WORKER_PARAM_FIELD_EVENT_FD     = UCS_BIT(4)  /**< External event file
                                                           descriptor */
};


/**
 * @ingroup UCP_WORKER
 * @brief UCP listener parameters field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_listener_params_t
 * are present. It is used to enable backward compatibility support.
 */
enum ucp_listener_params_field {
    /**
     * Sock address and length.
     */
    UCP_LISTENER_PARAM_FIELD_SOCK_ADDR           = UCS_BIT(0),

    /**
     * User's callback and argument for handling the creation of an endpoint.
     * */
    UCP_LISTENER_PARAM_FIELD_ACCEPT_HANDLER      = UCS_BIT(1),

    /**< User's callback and argument for handling the incoming connection
     *   request. */
    UCP_LISTENER_PARAM_FIELD_CONN_HANDLER        = UCS_BIT(2)
};


/**
 * @ingroup UCP_WORKER
 * @brief UCP worker address flags.
 *
 * The enumeration list describes possible UCP worker address flags, indicating
 * what needs to be included to the worker address returned by
 * @ref ucp_worker_query "ucp_worker_query()" routine.
 */
typedef enum {

    /**< Pack addresses of network devices only. Using such shortened addresses
     *   for the remote node peers will reduce the amount of wireup data being
     *   exchanged during connection establishment phase. */
    UCP_WORKER_ADDRESS_FLAG_NET_ONLY = UCS_BIT(0)
} ucp_worker_address_flags_t;


/**
 * @ingroup UCP_ENDPOINT
 * @brief UCP endpoint parameters field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_ep_params_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_ep_params_field {
    UCP_EP_PARAM_FIELD_REMOTE_ADDRESS    = UCS_BIT(0), /**< Address of remote
                                                            peer */
    UCP_EP_PARAM_FIELD_ERR_HANDLING_MODE = UCS_BIT(1), /**< Error handling mode.
                                                            @ref ucp_err_handling_mode_t */
    UCP_EP_PARAM_FIELD_ERR_HANDLER       = UCS_BIT(2), /**< Handler to process
                                                            transport level errors */
    UCP_EP_PARAM_FIELD_USER_DATA         = UCS_BIT(3), /**< User data pointer */
    UCP_EP_PARAM_FIELD_SOCK_ADDR         = UCS_BIT(4), /**< Socket address field */
    UCP_EP_PARAM_FIELD_FLAGS             = UCS_BIT(5), /**< Endpoint flags */
    UCP_EP_PARAM_FIELD_CONN_REQUEST      = UCS_BIT(6)  /**< Connection request field */
};


/**
 * @ingroup UCP_ENDPOINT
 * @brief UCP endpoint parameters flags.
 *
 * The enumeration list describes the endpoint's parameters flags supported by
 * @ref ucp_ep_create() function.
 */
enum ucp_ep_params_flags_field {
    UCP_EP_PARAMS_FLAGS_CLIENT_SERVER  = UCS_BIT(0),  /**< Using a client-server
                                                           connection establishment
                                                           mechanism.
                                                           @ref ucs_sock_addr_t
                                                           sockaddr field
                                                           must be provided and
                                                           contain the address
                                                           of the remote peer */
    UCP_EP_PARAMS_FLAGS_NO_LOOPBACK    = UCS_BIT(1)   /**< Avoid connecting the
                                                           endpoint to itself when
                                                           connecting the endpoint
                                                           to the same worker it
                                                           was created on.
                                                           Affects protocols which
                                                           send to a particular
                                                           remote endpoint, for
                                                           example stream */
};


/**
 * @ingroup UCP_ENDPOINT
 * @brief Close UCP endpoint modes.
 *
 * The enumeration is used to specify the behavior of @ref ucp_ep_close_nbx.
 */
typedef enum {
    UCP_EP_CLOSE_FLAG_FORCE = UCS_BIT(0) /**< @ref ucp_ep_close_nbx releases
                                              the endpoint without any
                                              confirmation from the peer. All
                                              outstanding requests will be
                                              completed with
                                              @ref UCS_ERR_CANCELED error.
                                              @note This mode may cause
                                              transport level errors on remote
                                              side, so it requires set
                                              @ref UCP_ERR_HANDLING_MODE_PEER
                                              for all endpoints created on
                                              both (local and remote) sides to
                                              avoid undefined behavior. If this
                                              flag is not set then
                                              @ref ucp_ep_close_nbx schedules
                                              flushes on all outstanding
                                              operations. */
} ucp_ep_close_flags_t;


/**
 * @ingroup UCP_ENDPOINT
 * @brief Close UCP endpoint modes.
 *
 * The enumeration is used to specify the behavior of @ref ucp_ep_close_nb.
 */
enum ucp_ep_close_mode {
    UCP_EP_CLOSE_MODE_FORCE         = 0, /**< @ref ucp_ep_close_nb releases
                                              the endpoint without any
                                              confirmation from the peer. All
                                              outstanding requests will be
                                              completed with
                                              @ref UCS_ERR_CANCELED error.
                                              @note This mode may cause
                                              transport level errors on remote
                                              side, so it requires set
                                              @ref UCP_ERR_HANDLING_MODE_PEER
                                              for all endpoints created on
                                              both (local and remote) sides to
                                              avoid undefined behavior. */
    UCP_EP_CLOSE_MODE_FLUSH         = 1  /**< @ref ucp_ep_close_nb schedules
                                              flushes on all outstanding
                                              operations. */
};


/**
 * @ingroup UCP_MEM
 * @brief UCP memory mapping parameters field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_mem_map_params_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_mem_map_params_field {
    UCP_MEM_MAP_PARAM_FIELD_ADDRESS     = UCS_BIT(0), /**< Address of the memory that
                                                           will be used in the
                                                           @ref ucp_mem_map routine. */
    UCP_MEM_MAP_PARAM_FIELD_LENGTH      = UCS_BIT(1), /**< The size of memory that
                                                           will be allocated or
                                                           registered in the
                                                           @ref ucp_mem_map routine.*/
    UCP_MEM_MAP_PARAM_FIELD_FLAGS       = UCS_BIT(2), /**< Allocation flags. */
    UCP_MEM_MAP_PARAM_FIELD_PROT        = UCS_BIT(3), /**< Memory protection mode. */
    UCP_MEM_MAP_PARAM_FIELD_MEMORY_TYPE = UCS_BIT(4)  /**< Memory type. */
};

/**
 * @ingroup UCP_MEM
 * @brief UCP memory advice parameters field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_mem_advise_params_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_mem_advise_params_field {
    UCP_MEM_ADVISE_PARAM_FIELD_ADDRESS = UCS_BIT(0), /**< Address of the memory */
    UCP_MEM_ADVISE_PARAM_FIELD_LENGTH  = UCS_BIT(1), /**< The size of memory */
    UCP_MEM_ADVISE_PARAM_FIELD_ADVICE  = UCS_BIT(2)  /**< Advice on memory usage */
};


/**
 * @ingroup UCP_CONTEXT
 * @brief UCP context attributes field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_context_attr_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_context_attr_field {
    UCP_ATTR_FIELD_REQUEST_SIZE = UCS_BIT(0), /**< UCP request size */
    UCP_ATTR_FIELD_THREAD_MODE  = UCS_BIT(1), /**< UCP context thread flag */
    UCP_ATTR_FIELD_MEMORY_TYPES = UCS_BIT(2)  /**< UCP supported memory types */
};


/**
 * @ingroup UCP_WORKER
 * @brief UCP worker attributes field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_worker_attr_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_worker_attr_field {
    UCP_WORKER_ATTR_FIELD_THREAD_MODE   = UCS_BIT(0), /**< UCP thread mode */
    UCP_WORKER_ATTR_FIELD_ADDRESS       = UCS_BIT(1), /**< UCP address */
    UCP_WORKER_ATTR_FIELD_ADDRESS_FLAGS = UCS_BIT(2), /**< UCP address flags */
    UCP_WORKER_ATTR_FIELD_MAX_AM_HEADER = UCS_BIT(3)  /**< Maximal header size
                                                           used by UCP AM API */
};


/**
 * @ingroup UCP_WORKER
 * @brief UCP listener attributes field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_listener_attr_t are
 * present. It is used to enable backward compatibility support.
 */
enum ucp_listener_attr_field {
    UCP_LISTENER_ATTR_FIELD_SOCKADDR = UCS_BIT(0) /**< Sockaddr used for listening */
};


/**
 * @ingroup UCP_WORKER
 * @brief UCP listener's connection request attributes field mask.
 *
 * The enumeration allows specifying which fields in @ref ucp_conn_request_attr_t
 * are present. It is used to enable backward compatibility support.
 */
enum ucp_conn_request_attr_field {
    UCP_CONN_REQUEST_ATTR_FIELD_CLIENT_ADDR = UCS_BIT(0) /**< Client's address */
};


/**
 * @ingroup UCP_DATATYPE
 * @brief UCP data type classification
 *
 * The enumeration list describes the datatypes supported by UCP.
 */
enum ucp_dt_type {
    UCP_DATATYPE_CONTIG  = 0,      /**< Contiguous datatype */
    UCP_DATATYPE_STRIDED = 1,      /**< Strided datatype */
    UCP_DATATYPE_IOV     = 2,      /**< Scatter-gather list with multiple pointers */
    UCP_DATATYPE_GENERIC = 7,      /**< Generic datatype with
                                        user-defined pack/unpack routines */
    UCP_DATATYPE_SHIFT   = 3,      /**< Number of bits defining
                                        the datatype classification */
    UCP_DATATYPE_CLASS_MASK = UCS_MASK(UCP_DATATYPE_SHIFT) /**< Data-type class
                                                                mask */
};


/**
 * @ingroup UCP_MEM
 * @brief UCP memory mapping flags.
 *
 * The enumeration list describes the memory mapping flags supported by @ref
 * ucp_mem_map() function.
 */
enum {
    UCP_MEM_MAP_NONBLOCK = UCS_BIT(0), /**< Complete the mapping faster, possibly by
                                            not populating the pages in the mapping
                                            up-front, and mapping them later when
                                            they are accessed by communication
                                            routines. */
    UCP_MEM_MAP_ALLOCATE = UCS_BIT(1), /**< Identify requirement for allocation,
                                            if passed address is not a null-pointer
                                            then it will be used as a hint or direct
                                            address for allocation. */
    UCP_MEM_MAP_FIXED    = UCS_BIT(2)  /**< Don't interpret address as a hint:
                                            place the mapping at exactly that
                                            address. The address must be a multiple
                                            of the page size. */
};


/**
 * @ingroup UCP_MEM
 * @brief UCP memory mapping protection mode.
 *
 * The enumeration list describes the memory mapping protections supported by the @ref
 * ucp_mem_map() function.
 */
enum {
    UCP_MEM_MAP_PROT_LOCAL_READ   = UCS_BIT(0),  /**< Enable local read access. */
    UCP_MEM_MAP_PROT_LOCAL_WRITE  = UCS_BIT(1),  /**< Enable local write access. */
    UCP_MEM_MAP_PROT_REMOTE_READ  = UCS_BIT(8),  /**< Enable remote read access. */
    UCP_MEM_MAP_PROT_REMOTE_WRITE = UCS_BIT(9)   /**< Enable remote write access. */
};


/**
 * @ingroup UCP_WORKER
 * @brief Flags for a UCP Active Message callback.
 *
 * Flags that indicate how to handle UCP Active Messages
 * Currently only UCP_AM_FLAG_WHOLE_MSG is supported,
 * which indicates the entire message is handled in one
 * callback.
 */
enum ucp_am_cb_flags {
    UCP_AM_FLAG_WHOLE_MSG = UCS_BIT(0)
};


/**
 * @ingroup UCP_WORKER
 * @brief Flags for sending a UCP Active Message.
 *
 * Flags dictate the behavior of @ref ucp_am_send_nb and @ref ucp_am_send_nbx
 * routines.
 */
enum ucp_send_am_flags {
    UCP_AM_SEND_FLAG_REPLY = UCS_BIT(0),             /**< Force relevant reply
                                                          endpoint to be passed to
                                                          the data callback on the
                                                          receiver. */
    UCP_AM_SEND_FLAG_EAGER = UCS_BIT(1),             /**< Force UCP to use only
                                                          eager protocol for AM sends. */
    UCP_AM_SEND_FLAG_RNDV  = UCS_BIT(2),             /**< Force UCP to use only
                                                          rendezvous protocol for
                                                          AM sends. */
    UCP_AM_SEND_REPLY      = UCP_AM_SEND_FLAG_REPLY  /**< Backward compatibility. */
};


/**
 * @ingroup UCP_ENDPOINT
 * @brief Descriptor flags for Active Message callback.
 *
 * In a callback, if flags is set to UCP_CB_PARAM_FLAG_DATA in
 * a callback then data was allocated, so if UCS_INPROGRESS is
 * returned from the callback, the data parameter will persist
 * and the user has to call @ref ucp_am_data_release when data is
 * no longer needed.
 */
enum ucp_cb_param_flags {
    UCP_CB_PARAM_FLAG_DATA = UCS_BIT(0)
};


/**
 * @ingroup UCP_COMM
 * @brief Atomic operation requested for ucp_atomic_post
 *
 * This enumeration defines which atomic memory operation should be
 * performed by the ucp_atomic_post family of fuctions. All of these are
 * non-fetching atomics and will not result in a request handle.
 */
typedef enum {
    UCP_ATOMIC_POST_OP_ADD, /**< Atomic add */
    UCP_ATOMIC_POST_OP_AND, /**< Atomic and */
    UCP_ATOMIC_POST_OP_OR,  /**< Atomic or  */
    UCP_ATOMIC_POST_OP_XOR, /**< Atomic xor */
    UCP_ATOMIC_POST_OP_LAST
} ucp_atomic_post_op_t;


/**
 * @ingroup UCP_COMM
 * @brief Atomic operation requested for ucp_atomic_fetch
 *
 * This enumeration defines which atomic memory operation should be performed
 * by the ucp_atomic_fetch family of functions. All of these functions
 * will fetch data from the remote node.
 */
typedef enum {
    UCP_ATOMIC_FETCH_OP_FADD,  /**< Atomic Fetch and add    */
    UCP_ATOMIC_FETCH_OP_SWAP,  /**< Atomic swap             */
    UCP_ATOMIC_FETCH_OP_CSWAP, /**< Atomic conditional swap */
    UCP_ATOMIC_FETCH_OP_FAND,  /**< Atomic Fetch and and    */
    UCP_ATOMIC_FETCH_OP_FOR,   /**< Atomic Fetch and or     */
    UCP_ATOMIC_FETCH_OP_FXOR,  /**< Atomic Fetch and xor    */
    UCP_ATOMIC_FETCH_OP_LAST
} ucp_atomic_fetch_op_t;


/**
 * @ingroup UCP_COMM
 * @brief Atomic operation requested for ucp_atomic_op_nbx
 *
 * This enumeration defines which atomic memory operation should be
 * performed by the @ref ucp_atomic_op_nbx routine.
 */
typedef enum {
    UCP_ATOMIC_OP_ADD,   /**< Atomic add  */
    UCP_ATOMIC_OP_SWAP,  /**< Atomic swap */
    UCP_ATOMIC_OP_CSWAP, /**< Atomic conditional swap */
    UCP_ATOMIC_OP_AND,   /**< Atomic and  */
    UCP_ATOMIC_OP_OR,    /**< Atomic or   */
    UCP_ATOMIC_OP_XOR,   /**< Atomic xor  */
    UCP_ATOMIC_OP_LAST
} ucp_atomic_op_t;


/**
 * @ingroup UCP_COMM
 * @brief Flags to define behavior of @ref ucp_stream_recv_nb function
 *
 * This enumeration defines behavior of @ref ucp_stream_recv_nb function.
 */
typedef enum {
    UCP_STREAM_RECV_FLAG_WAITALL = UCS_BIT(0)  /**< This flag requests that
                                                    the operation will not be
                                                    completed until all
                                                    requested data is received
                                                    and placed in the user
                                                    buffer. */
} ucp_stream_recv_flags_t;


/**
 * @ingroup UCP_COMM
 * @brief UCP operation fields and flags
 *
 * The enumeration allows specifying which fields in @ref ucp_request_param_t are
 * present and operation flags are used. It is used to enable backward
 * compatibility support.
 */
typedef enum {
    UCP_OP_ATTR_FIELD_REQUEST       = UCS_BIT(0),  /**< request field */
    UCP_OP_ATTR_FIELD_CALLBACK      = UCS_BIT(1),  /**< cb field */
    UCP_OP_ATTR_FIELD_USER_DATA     = UCS_BIT(2),  /**< user_data field */
    UCP_OP_ATTR_FIELD_DATATYPE      = UCS_BIT(3),  /**< datatype field */
    UCP_OP_ATTR_FIELD_FLAGS         = UCS_BIT(4),  /**< operation-specific flags */
    UCP_OP_ATTR_FIELD_REPLY_BUFFER  = UCS_BIT(5),  /**< reply_buffer field */
    UCP_OP_ATTR_FIELD_MEMORY_TYPE   = UCS_BIT(6),  /**< memory type field */
    UCP_OP_ATTR_FIELD_RECV_INFO     = UCS_BIT(7),  /**< recv_info field */

    UCP_OP_ATTR_FLAG_NO_IMM_CMPL    = UCS_BIT(16), /**< deny immediate completion */
    UCP_OP_ATTR_FLAG_FAST_CMPL      = UCS_BIT(17), /**< expedite local completion,
                                                        even if it delays remote 
                                                        data delivery. Note for
                                                        implementer: this option
                                                        can disable zero copy
                                                        and/or rendezvous protocols
                                                        which require
                                                        synchronization with the
                                                        remote peer before releasing
                                                        the local send buffer */
    UCP_OP_ATTR_FLAG_FORCE_IMM_CMPL = UCS_BIT(18)  /**< force immediate complete
                                                        operation, fail if the
                                                        operation cannot be
                                                        completed immediately */
} ucp_op_attr_t;


/**
 * @ingroup UCP_COMM
 * @brief UCP AM receive data parameter fields and flags
 *
 * The enumeration allows specifying which fields in @ref ucp_am_recv_param_t
 * are present and receive operation flags are used. It is used to enable
 * backward compatibility support.
 */
typedef enum {
    UCP_AM_RECV_ATTR_FIELD_REPLY_EP    = UCS_BIT(0),  /**< reply_ep field */

    /**
     * Indicates that the data provided in @ref ucp_am_recv_callback_t callback
     * can be held by the user. If UCS_INPROGRESS is returned from the callback,
     * the data parameter will persist and the user has to call
     * @ref ucp_am_data_release when data is no longer needed. This flag is
     * mutually exclusive with @a UCP_AM_RECV_ATTR_FLAG_RNDV.
     */
    UCP_AM_RECV_ATTR_FLAG_DATA         = UCS_BIT(16),

    /**
     * Indicates that the arriving data was sent using rendezvous protocol.
     * In this case @a data parameter of the @ref ucp_am_recv_callback_t points
     * to the internal UCP descriptor, which can be used for obtaining the actual
     * data by calling @ref ucp_am_recv_data_nbx routine. This flag is mutually
     * exclusive with @a UCP_AM_RECV_ATTR_FLAG_DATA.
     */
    UCP_AM_RECV_ATTR_FLAG_RNDV         = UCS_BIT(17)
} ucp_am_recv_attr_t;


/**
 * @ingroup UCP_COMM
 * @brief UCP AM receive data parameters fields and flags
 *
 * The enumeration allows specifying which fields in @ref ucp_am_handler_param_t
 * are present. It is used to enable backward compatibility support.
 */
enum ucp_am_handler_param_field {
    /**
     * Indicates that @ref ucp_am_handler_param_t.id field is valid.
     */
    UCP_AM_HANDLER_PARAM_FIELD_ID      = UCS_BIT(0),
    /**
     * Indicates that @ref ucp_am_handler_param_t.flags field is valid.
     */
    UCP_AM_HANDLER_PARAM_FIELD_FLAGS   = UCS_BIT(1),
    /**
     * Indicates that @ref ucp_am_handler_param_t.cb field is valid.
     */
    UCP_AM_HANDLER_PARAM_FIELD_CB      = UCS_BIT(2),
    /**
     * Indicates that @ref ucp_am_handler_param_t.arg field is valid.
     */
    UCP_AM_HANDLER_PARAM_FIELD_ARG     = UCS_BIT(3)
};


/**
 * @ingroup UCP_DATATYPE
 * @brief Generate an identifier for contiguous data type.
 *
 * This macro creates an identifier for contiguous datatype that is defined by
 * the size of the basic element.
 *
 * @param [in]  _elem_size    Size of the basic element of the type.
 *
 * @return Data-type identifier.
 *
 * @note In case of partial receive, the buffer will be filled with integral
 *       count of elements.
 */
#define ucp_dt_make_contig(_elem_size) \
    (((ucp_datatype_t)(_elem_size) << UCP_DATATYPE_SHIFT) | UCP_DATATYPE_CONTIG)


/**
 * @ingroup UCP_DATATYPE
 * @brief Generate an identifier for Scatter-gather IOV data type.
 *
 * This macro creates an identifier for datatype of scatter-gather list
 * with multiple pointers
 *
 * @return Data-type identifier.
 *
 * @note In the event of partial receive, @ref ucp_dt_iov_t::buffer can be
 *       filled with any number of bytes according to its
 *       @ref ucp_dt_iov_t::length.
 */
#define ucp_dt_make_iov() ((ucp_datatype_t)UCP_DATATYPE_IOV)


/**
 * @ingroup UCP_DATATYPE
 * @brief Structure for scatter-gather I/O.
 *
 * This structure is used to specify a list of buffers which can be used
 * within a single data transfer function call.
 *
 * @note If @a length is zero, the memory pointed to by @a buffer
 *       will not be accessed. Otherwise, @a buffer must point to valid memory.
 */
typedef struct ucp_dt_iov {
    void   *buffer;   /**< Pointer to a data buffer */
    size_t  length;   /**< Length of the @a buffer in bytes */
} ucp_dt_iov_t;


/**
 * @ingroup UCP_DATATYPE
 * @brief UCP generic data type descriptor
 *
 * This structure provides a generic datatype descriptor that
 * is used for definition of application defined datatypes.

 * Typically, the descriptor is used for an integration with datatype
 * engines implemented within MPI and SHMEM implementations.
 *
 * @note In case of partial receive, any amount of received data is acceptable
 *       which matches buffer size.
 */
typedef struct ucp_generic_dt_ops {

    /**
     * @ingroup UCP_DATATYPE
     * @brief Start a packing request.
     *
     * The pointer refers to application defined start-to-pack routine. It will
     * be called from the @ref ucp_tag_send_nb routine.
     *
     * @param [in]  context        User-defined context.
     * @param [in]  buffer         Buffer to pack.
     * @param [in]  count          Number of elements to pack into the buffer.
     *
     * @return  A custom state that is passed to the following
     *          @ref ucp_generic_dt_ops::pack "pack()" routine.
     */
    void* (*start_pack)(void *context, const void *buffer, size_t count);

    /**
     * @ingroup UCP_DATATYPE
     * @brief Start an unpacking request.
     *
     * The pointer refers to application defined start-to-unpack routine. It will
     * be called from the @ref ucp_tag_recv_nb routine.
     *
     * @param [in]  context        User-defined context.
     * @param [in]  buffer         Buffer to unpack to.
     * @param [in]  count          Number of elements to unpack in the buffer.
     *
     * @return  A custom state that is passed later to the following
     *          @ref ucp_generic_dt_ops::unpack "unpack()" routine.
     */
    void* (*start_unpack)(void *context, void *buffer, size_t count);

    /**
     * @ingroup UCP_DATATYPE
     * @brief Get the total size of packed data.
     *
     * The pointer refers to user defined routine that returns the size of data
     * in a packed format.
     *
     * @param [in]  state          State as returned by
     *                             @ref ucp_generic_dt_ops::start_pack
     *                             "start_pack()" routine.
     *
     * @return  The size of the data in a packed form.
     */
    size_t (*packed_size)(void *state);

    /**
     * @ingroup UCP_DATATYPE
     * @brief Pack data.
     *
     * The pointer refers to application defined pack routine.
     *
     * @param [in]  state          State as returned by
     *                             @ref ucp_generic_dt_ops::start_pack
     *                             "start_pack()" routine.
     * @param [in]  offset         Virtual offset in the output stream.
     * @param [in]  dest           Destination to pack the data to.
     * @param [in]  max_length     Maximal length to pack.
     *
     * @return The size of the data that was written to the destination buffer.
     *         Must be less than or equal to @e max_length.
     */
    size_t (*pack) (void *state, size_t offset, void *dest, size_t max_length);

    /**
     * @ingroup UCP_DATATYPE
     * @brief Unpack data.
     *
     * The pointer refers to application defined unpack routine.
     *
     * @param [in]  state          State as returned by
     *                             @ref ucp_generic_dt_ops::start_unpack
     *                             "start_unpack()" routine.
     * @param [in]  offset         Virtual offset in the input stream.
     * @param [in]  src            Source to unpack the data from.
     * @param [in]  length         Length to unpack.
     *
     * @return UCS_OK or an error if unpacking failed.
     */
    ucs_status_t (*unpack)(void *state, size_t offset, const void *src, size_t length);

    /**
     * @ingroup UCP_DATATYPE
     * @brief Finish packing/unpacking.
     *
     * The pointer refers to application defined finish routine.
     *
     * @param [in]  state          State as returned by
     *                             @ref ucp_generic_dt_ops::start_pack
     *                             "start_pack()"
     *                             and
     *                             @ref ucp_generic_dt_ops::start_unpack
     *                             "start_unpack()"
     *                             routines.
     */
    void (*finish)(void *state);
} ucp_generic_dt_ops_t;


/**
 * @ingroup UCP_CONFIG
 * @brief Tuning parameters for UCP library.
 *
 * The structure defines the parameters that are used for
 * UCP library tuning during UCP library @ref ucp_init "initialization".
 *
 * @note UCP library implementation uses the @ref ucp_feature "features"
 * parameter to optimize the library functionality that minimize memory
 * footprint. For example, if the application does not require send/receive
 * semantics UCP library may avoid allocation of expensive resources associated with
 * send/receive queues.
 */
typedef struct ucp_params {
    /**
     * Mask of valid fields in this structure, using bits from @ref ucp_params_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                           field_mask;

    /**
     * UCP @ref ucp_feature "features" that are used for library
     * initialization. It is recommended for applications only to request
     * the features that are required for an optimal functionality
     * This field must be specified.
     */
    uint64_t                           features;

    /**
     * The size of a reserved space in a non-blocking requests. Typically
     * applications use this space for caching own structures in order to avoid
     * costly memory allocations, pointer dereferences, and cache misses.
     * For example, MPI implementation can use this memory for caching MPI
     * descriptors
     * This field defaults to 0 if not specified.
     */
    size_t                             request_size;

    /**
     * Pointer to a routine that is used for the request initialization.
     * This function will be called only on the very first time a request memory
     * is initialized, and may not be called again if a request is reused.
     * If a request should be reset before the next reuse, it can be done before
     * calling @ref ucp_request_free.
     *
     * @e NULL can be used if no such is function required, which is also the
     * default if this field is not specified by @ref field_mask.
     */
    ucp_request_init_callback_t        request_init;

    /**
     * Pointer to a routine that is responsible for final cleanup of the memory
     * associated with the request. This routine may not be called every time a
     * request is released. For some implementations, the cleanup call may be
     * delayed and only invoked at @ref ucp_worker_destroy.
     *
     * @e NULL can be used if no such function is required, which is also the
     * default if this field is not specified by @ref field_mask.
     */
    ucp_request_cleanup_callback_t     request_cleanup;

    /**
     * Mask which specifies particular bits of the tag which can uniquely
     * identify the sender (UCP endpoint) in tagged operations.
     * This field defaults to 0 if not specified.
     */
    uint64_t                           tag_sender_mask;

    /**
     * This flag indicates if this context is shared by multiple workers
     * from different threads. If so, this context needs thread safety
     * support; otherwise, the context does not need to provide thread
     * safety.
     * For example, if the context is used by single worker, and that
     * worker is shared by multiple threads, this context does not need
     * thread safety; if the context is used by worker 1 and worker 2,
     * and worker 1 is used by thread 1 and worker 2 is used by thread 2,
     * then this context needs thread safety.
     * Note that actual thread mode may be different from mode passed
     * to @ref ucp_init. To get actual thread mode use
     * @ref ucp_context_query.
     */
    int                                mt_workers_shared;

    /**
     * An optimization hint of how many endpoints will be created on this context.
     * For example, when used from MPI or SHMEM libraries, this number will specify
     * the number of ranks (or processing elements) in the job.
     * Does not affect semantics, but only transport selection criteria and the
     * resulting performance.
     * The value can be also set by UCX_NUM_EPS environment variable. In such case
     * it will override the number of endpoints set by @e estimated_num_eps
     */
    size_t                             estimated_num_eps;

    /**
     * An optimization hint for a single node. For example, when used from MPI or
     * OpenSHMEM libraries, this number will specify the number of Processes Per
     * Node (PPN) in the job. Does not affect semantics, only transport selection
     * criteria and the resulting performance.
     * The value can be also set by the UCX_NUM_PPN environment variable, which
     * will override the number of endpoints set by @e estimated_num_ppn
     */
    size_t                             estimated_num_ppn;
} ucp_params_t;


/**
 * @ingroup UCP_CONTEXT
 * @brief Context attributes.
 *
 * The structure defines the attributes which characterize
 * the particular context.
 */
typedef struct ucp_context_attr {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_context_attr_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t              field_mask;

    /**
     * Size of UCP non-blocking request. When pre-allocated request is used
     * (e.g. in @ref ucp_tag_recv_nbr) it should have enough space to fit
     * UCP request data, which is defined by this value.
     */
    size_t                request_size;

    /**
     * Thread safe level of the context. For supported thread levels please
     * see @ref ucs_thread_mode_t.
     */
    ucs_thread_mode_t     thread_mode;

    /**
     * Mask of which memory types are supported, for supported memory types
     * please see @ref ucs_memory_type_t.
     */
    uint64_t              memory_types;
} ucp_context_attr_t;


/**
 * @ingroup UCP_WORKER
 * @brief UCP worker attributes.
 *
 * The structure defines the attributes which characterize
 * the particular worker.
 */
typedef struct ucp_worker_attr {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_worker_attr_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t              field_mask;

    /**
     * Thread safe level of the worker.
     */
    ucs_thread_mode_t     thread_mode;

    /**
     * Flags indicating requested details of the worker address.
     * If @ref UCP_WORKER_ATTR_FIELD_ADDRESS_FLAGS bit is set in the field_mask,
     * this value should be set as well. Possible flags are specified
     * in @ref ucp_worker_address_flags_t. @note This is an input attribute.
     */
    uint32_t              address_flags;

    /**
     * Worker address, which can be passed to remote instances of the UCP library
     * in order to connect to this worker. The memory for the address handle is
     * allocated by @ref ucp_worker_query "ucp_worker_query()" routine, and
     * must be released by using @ref ucp_worker_release_address
     * "ucp_worker_release_address()" routine.
     */
    ucp_address_t         *address;

    /**
     * Size of worker address in bytes.
     */
    size_t                address_length;

    /**
     * Maximal allowed header size for @ref ucp_am_send_nbx routine
     */
    size_t                max_am_header;
} ucp_worker_attr_t;


/**
 * @ingroup UCP_WORKER
 * @brief Tuning parameters for the UCP worker.
 *
 * The structure defines the parameters that are used for the
 * UCP worker tuning during the UCP worker @ref ucp_worker_create "creation".
 */
typedef struct ucp_worker_params {
    /**
     * Mask of valid fields in this structure, using bits from @ref ucp_worker_params_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                field_mask;

    /**
     * The parameter thread_mode suggests the thread safety mode which worker
     * and the associated resources should be created with. This is an
     * optional parameter. The default value is UCS_THREAD_MODE_SINGLE and
     * it is used when the value of the parameter is not set. When this
     * parameter along with its corresponding bit in the
     * field_mask - UCP_WORKER_PARAM_FIELD_THREAD_MODE is set, the
     * @ref ucp_worker_create attempts to create worker with this thread mode.
     * The thread mode with which worker is created can differ from the
     * suggested mode. The actual thread mode of the worker should be obtained
     * using the query interface @ref ucp_worker_query.
     */
    ucs_thread_mode_t       thread_mode;

    /**
     * Mask of which CPUs worker resources should preferably be allocated on.
     * This value is optional.
     * If it's not set (along with its corresponding bit in the field_mask -
     * UCP_WORKER_PARAM_FIELD_CPU_MASK), resources are allocated according to
     * system's default policy.
     */
    ucs_cpu_set_t           cpu_mask;

    /**
     * Mask of events (@ref ucp_wakeup_event_t) which are expected on wakeup.
     * This value is optional.
     * If it's not set (along with its corresponding bit in the field_mask -
     * UCP_WORKER_PARAM_FIELD_EVENTS), all types of events will trigger on
     * wakeup.
     */
    unsigned                events;

    /**
     * User data associated with the current worker.
     * This value is optional.
     * If it's not set (along with its corresponding bit in the field_mask -
     * UCP_WORKER_PARAM_FIELD_USER_DATA), it will default to NULL.
     */
    void                    *user_data;

    /**
     * External event file descriptor.
     * This value is optional.
     * If @ref UCP_WORKER_PARAM_FIELD_EVENT_FD is set in the field_mask, events
     * on the worker will be reported on the provided event file descriptor. In
     * this case, calling @ref ucp_worker_get_efd will result in an error.
     * The provided file descriptor must be capable of aggregating notifications
     * for arbitrary events, for example @c epoll(7) on Linux systems.
     * @ref user_data will be used as the event user-data on systems which
     * support it. For example, on Linux, it will be placed in
     * @c epoll_data_t::ptr, when returned from @c epoll_wait(2).
     *
     * Otherwise, events will be reported to the event file descriptor returned
     * from @ref ucp_worker_get_efd().
     */
    int                     event_fd;

} ucp_worker_params_t;


/**
 * @ingroup UCP_WORKER
 * @brief UCP listener attributes.
 *
 * The structure defines the attributes which characterize
 * the particular listener.
 */
typedef struct ucp_listener_attr {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_listener_attr_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                field_mask;

    /**
     * Sockaddr on which this listener is listening for incoming connection
     * requests.
     */
    struct sockaddr_storage sockaddr;
} ucp_listener_attr_t;


/**
 * @ingroup UCP_WORKER
 * @brief UCP listener's connection request attributes.
 *
 * The structure defines the attributes that characterize
 * the particular connection request received on the server side.
 */
typedef struct ucp_conn_request_attr {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_conn_request_attr_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                field_mask;

    /**
     * The address of the remote client that sent the connection request to the
     * server.
     */
    struct sockaddr_storage client_address;
} ucp_conn_request_attr_t;


/**
 * @ingroup UCP_WORKER
 * @brief Parameters for a UCP listener object.
 *
 * This structure defines parameters for @ref ucp_listener_create, which is used to
 * listen for incoming client/server connections.
 */
typedef struct ucp_listener_params {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_listener_params_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                            field_mask;

    /**
     * An address in the form of a sockaddr.
     * This field is mandatory for filling (along with its corresponding bit
     * in the field_mask - @ref UCP_LISTENER_PARAM_FIELD_SOCK_ADDR).
     * The @ref ucp_listener_create routine will return with an error if sockaddr
     * is not specified.
     */
    ucs_sock_addr_t                     sockaddr;

    /**
     * Handler to endpoint creation in a client-server connection flow.
     * In order for the callback inside this handler to be invoked, the
     * UCP_LISTENER_PARAM_FIELD_ACCEPT_HANDLER needs to be set in the
     * field_mask.
     */
    ucp_listener_accept_handler_t       accept_handler;

    /**
     * Handler of an incoming connection request in a client-server connection
     * flow. In order for the callback inside this handler to be invoked, the
     * @ref UCP_LISTENER_PARAM_FIELD_CONN_HANDLER needs to be set in the
     * field_mask.
     */
    ucp_listener_conn_handler_t         conn_handler;
} ucp_listener_params_t;


/**
 * @ingroup UCP_ENDPOINT
 * @brief Output parameter of @ref ucp_stream_worker_poll function.
 *
 * The structure defines the endpoint and its user data.
 */
typedef struct ucp_stream_poll_ep {
    /**
     * Endpoint handle.
     */
    ucp_ep_h    ep;

    /**
     * User data associated with an endpoint passed in
     * @ref ucp_ep_params_t::user_data.
     */
    void        *user_data;

    /**
     * Reserved for future use.
     */
    unsigned    flags;

    /**
     * Reserved for future use.
     */
    uint8_t     reserved[16];
} ucp_stream_poll_ep_t;


/**
 * @ingroup UCP_MEM
 * @brief Tuning parameters for the UCP memory mapping.
 *
 * The structure defines the parameters that are used for the
 * UCP memory mapping tuning during the @ref ucp_mem_map "ucp_mem_map" routine.
 */
typedef struct ucp_mem_map_params {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_mem_map_params_field.
     * Fields not specified in this mask will be ignored.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                field_mask;

    /**
     * If the address is not NULL, the routine maps (registers) the memory segment
     * pointed to by this address.
     * If the pointer is NULL, the library allocates mapped (registered) memory
     * segment and returns its address in this argument.
     * Therefore, this value is optional.
     * If it's not set (along with its corresponding bit in the field_mask -
     * @ref UCP_MEM_MAP_PARAM_FIELD_ADDRESS), the ucp_mem_map routine will consider
     * address as set to NULL and will allocate memory.
     */
     void                   *address;

     /**
      * Length (in bytes) to allocate or map (register).
      * This field is mandatory for filling (along with its corresponding bit
      * in the field_mask - @ref UCP_MEM_MAP_PARAM_FIELD_LENGTH).
      * The @ref ucp_mem_map routine will return with an error if the length isn't
      * specified.
      */
     size_t                 length;

     /**
      * Allocation flags, e.g. @ref UCP_MEM_MAP_NONBLOCK.
      * This value is optional.
      * If it's not set (along with its corresponding bit in the field_mask -
      * @ref UCP_MEM_MAP_PARAM_FIELD_FLAGS), the @ref ucp_mem_map routine will
      * consider the flags as set to zero.
      */
     unsigned               flags;

     /**
      * Memory protection mode, e.g. @ref UCP_MEM_MAP_PROT_LOCAL_READ.
      * This value is optional.
      * If it's not set, the @ref ucp_mem_map routine will consider
      * the flags as set to UCP_MEM_MAP_PROT_LOCAL_READ|UCP_MEM_MAP_PROT_LOCAL_WRITE|
      * UCP_MEM_MAP_PROT_REMOTE_READ|UCP_MEM_MAP_PROT_REMOTE_WRITE.
      */
     unsigned               prot;

     /*
      * Memory type (for possible memory types see @ref ucs_memory_type_t)
      * It is an optimization hint to avoid memory type detection for map buffer.
      * The meaning of this field depends on the operation type.
      *
      * - Memory allocation: (@ref UCP_MEM_MAP_ALLOCATE flag is set) This field
      *    specifies the type of memory to allocate. If it's not set (along with its
      *    corresponding bit in the field_mask - @ref UCP_MEM_MAP_PARAM_FIELD_MEMORY_TYPE),
      *    @ref UCS_MEMORY_TYPE_HOST will be assumed by default.
      *
      * - Memory registration: This field specifies the type of memory which is
      *    pointed by @ref ucp_mem_map_params.address. If it's not set (along with its
      *    corresponding bit in the field_mask - @ref UCP_MEM_MAP_PARAM_FIELD_MEMORY_TYPE),
      *    or set to @ref UCS_MEMORY_TYPE_UNKNOWN, the memory type will be dectected
      *    internally.
      */
     ucs_memory_type_t      memory_type;
} ucp_mem_map_params_t;


/**
 * @ingroup UCP_CONTEXT
 * @brief UCP receive information descriptor
 *
 * The UCP receive information descriptor is allocated by application and filled
 * in with the information about the received message by @ref ucp_tag_probe_nb
 * or @ref ucp_tag_recv_request_test routines or
 * @ref ucp_tag_recv_callback_t callback argument.
 */
struct ucp_tag_recv_info {
    /** Sender tag */
    ucp_tag_t                              sender_tag;
    /** The size of the received data */
    size_t                                 length;
};


/**
 * @ingroup UCP_CONTEXT
 * @brief Operation parameters passed to @ref ucp_tag_send_nbx,
 *        @ref ucp_tag_send_sync_nbx, @ref ucp_tag_recv_nbx, @ref ucp_put_nbx,
 *        @ref ucp_get_nbx, @ref ucp_am_send_nbx and @ref ucp_am_recv_data_nbx.
 *
 * The structure @ref ucp_request_param_t is used to specify datatype of
 * operation, provide user request in case the external request is used,
 * set completion callback and custom user data passed to this callback.
 *
 * Example: implementation of function to send contiguous buffer to ep and
 *          invoke callback function at operation completion. If the
 *          operation completed immediately (status == UCS_OK) then
 *          callback is not called.
 *
 * @code{.c}
 * ucs_status_ptr_t send_data(ucp_ep_h ep, void *buffer, size_t length,
 *                            ucp_tag_t tag, void *request)
 * {
 *     ucp_request_param_t param = {
 *         .op_attr_mask               = UCP_OP_ATTR_FIELD_CALLBACK |
 *                                       UCP_OP_ATTR_FIELD_REQUEST,
 *         .request                    = request,
 *         .cb.ucp_send_nbx_callback_t = custom_send_callback_f,
 *         .user_data                  = pointer_to_user_context_passed_to_cb
 *     };
 *
 *     ucs_status_ptr_t status;
 *
 *     status = ucp_tag_send_nbx(ep, buffer, length, tag, &param);
 *     if (UCS_PTR_IS_ERR(status)) {
 *         handle_error(status);
 *     } else if (status == UCS_OK) {
 *         // operation is completed
 *     }
 *
 *     return status;
 * }
 * @endcode
 */
typedef struct {
    /**
     * Mask of valid fields in this structure and operation flags, using
     * bits from @ref ucp_op_attr_t. Fields not specified in this mask will be
     * ignored. Provides ABI compatibility with respect to adding new fields.
     */
    uint32_t       op_attr_mask;

    /* Operation specific flags. */
    uint32_t       flags;

    /**
     * Request handle allocated by the user. There should
     * be at least UCP request size bytes of available
     * space before the @a request. The size of the UCP request
     * can be obtained by @ref ucp_context_query function.
     */
    void          *request;

    /**
     * Callback function that is invoked whenever the
     * send or receive operation is completed.
     */
    union {
        ucp_send_nbx_callback_t         send;
        ucp_tag_recv_nbx_callback_t     recv;
        ucp_stream_recv_nbx_callback_t  recv_stream;
        ucp_am_recv_data_nbx_callback_t recv_am;
    }              cb;

    /**
     * Datatype descriptor for the elements in the buffer. In case the
     * op_attr_mask & UCP_OP_ATTR_FIELD_DATATYPE bit is not set, then use
     * default datatype ucp_dt_make_contig(1)
     */
    ucp_datatype_t datatype;

    /**
     * Pointer to user data passed to callback function.
     */
    void          *user_data;

    /**
     * Reply buffer. Can be used for storing operation result, for example by
     * @ref ucp_atomic_op_nbx.
     */
    void          *reply_buffer;

    /**
     * Memory type of the buffer. see @ref ucs_memory_type_t for possible memory types.
     * An optimization hint to avoid memory type detection for request buffer.
     * If this value is not set (along with its corresponding bit in the op_attr_mask -
     * @ref UCP_OP_ATTR_FIELD_MEMORY_TYPE), then use default @ref UCS_MEMORY_TYPE_UNKNOWN
     * which means the memory type will be detected internally.
     */
    ucs_memory_type_t memory_type;

    /**
     * Pointer to the information where received data details are stored
     * in case of an immediate completion of receive operation. The user has to
     * provide a pointer to valid memory/variable which will be updated on function
     * return.
     */
    union {
        size_t              *length;   /* Length of received message in bytes.
                                          Relevant for non-tagged receive
                                          operations. */
        ucp_tag_recv_info_t *tag_info; /* Information about received message.
                                          Relevant for @a ucp_tag_recv_nbx
                                          function. */
    } recv_info;
} ucp_request_param_t;


/**
 * @ingroup UCP_WORKER
 * @brief Active Message handler parameters passed to
 *        @ref ucp_worker_set_am_recv_handler routine.
 */
typedef struct ucp_am_handler_param {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_am_handler_param_field. Fields not specified in this mask will
     * be ignored. Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                 field_mask;

    /**
     * Active Message id.
     */
    unsigned                 id;

    /**
     * Handler flags as defined by @ref ucp_am_cb_flags.
     */
    uint32_t                 flags;

    /**
     * Active Message callback. To clear the already set callback, this value
     * should be set to NULL.
     */
    ucp_am_recv_callback_t   cb;

    /**
     * Active Message argument, which will be passed in to every invocation of
     * @ref ucp_am_recv_callback_t function as the @a arg argument.
     */
    void                     *arg;
} ucp_am_handler_param_t;


/**
 * @ingroup UCP_WORKER
 * @brief Operation parameters provided in @ref ucp_am_recv_callback_t callback.
 */
struct ucp_am_recv_param {
    /**
     * Mask of valid fields in this structure and receive operation flags, using
     * bits from @ref ucp_am_recv_attr_t. Fields not specified in this mask will
     * be ignored. Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t           recv_attr;

    /**
     * Endpoint, which can be used for reply to this message.
     */
    ucp_ep_h           reply_ep;
};


/**
 * @ingroup UCP_CONFIG
 * @brief Read UCP configuration descriptor
 *
 * The routine fetches the information about UCP library configuration from
 * the run-time environment. Then, the fetched descriptor is used for
 * UCP library @ref ucp_init "initialization". The Application can print out the
 * descriptor using @ref ucp_config_print "print" routine. In addition
 * the application is responsible for @ref ucp_config_release "releasing" the
 * descriptor back to the UCP library.
 *
 * @param [in]  env_prefix    If non-NULL, the routine searches for the
 *                            environment variables that start with
 *                            @e \<env_prefix\>_UCX_ prefix.
 *                            Otherwise, the routine searches for the
 *                            environment variables that start with
 *                            @e UCX_ prefix.
 * @param [in]  filename      If non-NULL, read configuration from the file
 *                            defined by @e filename. If the file does not
 *                            exist, it will be ignored and no error reported
 *                            to the application.
 * @param [out] config_p      Pointer to configuration descriptor as defined by
 *                            @ref ucp_config_t "ucp_config_t".
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_config_read(const char *env_prefix, const char *filename,
                             ucp_config_t **config_p);


/**
 * @ingroup UCP_CONFIG
 * @brief Release configuration descriptor
 *
 * The routine releases the configuration descriptor that was allocated through
 * @ref ucp_config_read "ucp_config_read()" routine.
 *
 * @param [out] config        Configuration descriptor as defined by
 *                            @ref ucp_config_t "ucp_config_t".
 */
void ucp_config_release(ucp_config_t *config);


/**
 * @ingroup UCP_CONFIG
 * @brief Modify context configuration.
 *
 * The routine changes one configuration setting stored in @ref ucp_config_t
 * "configuration" descriptor.
 *
 * @param [in]  config        Configuration to modify.
 * @param [in]  name          Configuration variable name.
 * @param [in]  value         Value to set.
 *
 * @return Error code.
 */
ucs_status_t ucp_config_modify(ucp_config_t *config, const char *name,
                               const char *value);


/**
 * @ingroup UCP_CONFIG
 * @brief Print configuration information
 *
 * The routine prints the configuration information that is stored in
 * @ref ucp_config_t "configuration" descriptor.
 *
 * @todo Expose ucs_config_print_flags_t
 *
 * @param [in]  config        @ref ucp_config_t "Configuration descriptor"
 *                            to print.
 * @param [in]  stream        Output stream to print the configuration to.
 * @param [in]  title         Configuration title to print.
 * @param [in]  print_flags   Flags that control various printing options.
 */
void ucp_config_print(const ucp_config_t *config, FILE *stream,
                      const char *title, ucs_config_print_flags_t print_flags);


/**
 * @ingroup UCP_CONTEXT
 * @brief Get UCP library version.
 *
 * This routine returns the UCP library version.
 *
 * @param [out] major_version       Filled with library major version.
 * @param [out] minor_version       Filled with library minor version.
 * @param [out] release_number      Filled with library release number.
 */
void ucp_get_version(unsigned *major_version, unsigned *minor_version,
                     unsigned *release_number);


/**
 * @ingroup UCP_CONTEXT
 * @brief Get UCP library version as a string.
 *
 * This routine returns the UCP library version as a string which consists of:
 * "major.minor.release".
 */
const char *ucp_get_version_string(void);


/** @cond PRIVATE_INTERFACE */
/**
 * @ingroup UCP_CONTEXT
 * @brief UCP context initialization with particular API version.
 *
 *  This is an internal routine used to check compatibility with a particular
 * API version. @ref ucp_init should be used to create UCP context.
 */
ucs_status_t ucp_init_version(unsigned api_major_version, unsigned api_minor_version,
                              const ucp_params_t *params, const ucp_config_t *config,
                              ucp_context_h *context_p);
/** @endcond */


/**
 * @ingroup UCP_CONTEXT
 * @brief UCP context initialization.
 *
 * This routine creates and initializes a @ref ucp_context_h
 * "UCP application context".
 *
 * @warning This routine must be called before any other UCP function
 * call in the application.
 *
 * This routine checks API version compatibility, then discovers the available
 * network interfaces, and initializes the network resources required for
 * discovering of the network and memory related devices.
 *  This routine is responsible for initialization all information required for
 * a particular application scope, for example, MPI application, OpenSHMEM
 * application, etc.
 *
 * @note
 * @li Higher level protocols can add additional communication isolation, as
 * MPI does with it's communicator object. A single communication context may
 * be used to support multiple MPI communicators.
 * @li The context can be used to isolate the communication that corresponds to
 * different protocols. For example, if MPI and OpenSHMEM are using UCP to
 * isolate the MPI communication from the OpenSHMEM communication, users should
 * use different application context for each of the communication libraries.
 *
 * @param [in]  config        UCP configuration descriptor allocated through
 *                            @ref ucp_config_read "ucp_config_read()" routine.
 * @param [in]  params        User defined @ref ucp_params_t configurations for the
 *                            @ref ucp_context_h "UCP application context".
 * @param [out] context_p     Initialized @ref ucp_context_h
 *                            "UCP application context".
 *
 * @return Error code as defined by @ref ucs_status_t
 */
static inline ucs_status_t ucp_init(const ucp_params_t *params,
                                    const ucp_config_t *config,
                                    ucp_context_h *context_p)
{
    return ucp_init_version(UCP_API_MAJOR, UCP_API_MINOR, params, config,
                            context_p);
}


/**
 * @ingroup UCP_CONTEXT
 * @brief Release UCP application context.
 *
 * This routine finalizes and releases the resources associated with a
 * @ref ucp_context_h "UCP application context".
 *
 * @warning An application cannot call any UCP routine
 * once the UCP application context released.
 *
 * The cleanup process releases and shuts down all resources associated    with
 * the application context. After calling this routine, calling any UCP
 * routine without calling @ref ucp_init "UCP initialization routine" is invalid.
 *
 * @param [in] context_p   Handle to @ref ucp_context_h
 *                         "UCP application context".
 */
void ucp_cleanup(ucp_context_h context_p);


/**
 * @ingroup UCP_CONTEXT
 * @brief Get attributes specific to a particular context.
 *
 * This routine fetches information about the context.
 *
 * @param [in]  context_p  Handle to @ref ucp_context_h
 *                         "UCP application context".
 *
 * @param [out] attr       Filled with attributes of @p context_p context.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_context_query(ucp_context_h context_p,
                               ucp_context_attr_t *attr);


/**
 * @ingroup UCP_CONTEXT
 * @brief Print context information.
 *
 * This routine prints information about the context configuration: including
 * memory domains, transport resources, and other useful information associated
 * with the context.
 *
 * @param [in] context      Print this context object's configuration.
 * @param [in] stream       Output stream on which to print the information.
 */
void ucp_context_print_info(const ucp_context_h context, FILE *stream);


/**
 * @ingroup UCP_WORKER
 * @brief Create a worker object.
 *
 * This routine allocates and initializes a @ref ucp_worker_h "worker" object.
 * Each worker is associated with one and only one @ref ucp_context_h
 * "application" context.  In the same time, an application context can create
 * multiple @ref ucp_worker_h "workers" in order to enable concurrent access to
 * communication resources. For example, application can allocate a dedicated
 * worker for each application thread, where every worker can be progressed
 * independently of others.
 *
 * @note The worker object is allocated within context of the calling thread
 *
 * @param [in] context     Handle to @ref ucp_context_h
 *                         "UCP application context".
 * @param [in] params      User defined @ref ucp_worker_params_t configurations for the
 *                         @ref ucp_worker_h "UCP worker".
 * @param [out] worker_p   A pointer to the worker object allocated by the
 *                         UCP library
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_create(ucp_context_h context,
                               const ucp_worker_params_t *params,
                               ucp_worker_h *worker_p);


/**
 * @ingroup UCP_WORKER
 * @brief Destroy a worker object.
 *
 * This routine releases the resources associated with a
 * @ref ucp_worker_h "UCP worker".
 *
 * @warning Once the UCP worker destroy the worker handle cannot be used with any
 * UCP routine.
 *
 * The destroy process releases and shuts down all resources associated    with
 * the @ref ucp_worker_h "worker".
 *
 * @param [in]  worker        Worker object to destroy.
 */
void ucp_worker_destroy(ucp_worker_h worker);


/**
 * @ingroup UCP_WORKER
 * @brief Get attributes specific to a particular worker.
 *
 * This routine fetches information about the worker.
 *
 * @param [in]  worker     Worker object to query.
 * @param [out] attr       Filled with attributes of worker.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_query(ucp_worker_h worker,
                              ucp_worker_attr_t *attr);


/**
 * @ingroup UCP_WORKER
 * @brief Print information about the worker.
 *
 * This routine prints information about the protocols being used, thresholds,
 * UCT transport methods, and other useful information associated with the worker.
 *
 * @param [in] worker       Worker object to print information for.
 * @param [in] stream       Output stream to print the information to.
 */
void ucp_worker_print_info(ucp_worker_h worker, FILE *stream);


/**
 * @ingroup UCP_WORKER
 * @brief Get the address of the worker object.
 *
 * This routine returns the address of the worker object.  This address can be
 * passed to remote instances of the UCP library in order to connect to this
 * worker. The memory for the address handle is allocated by this function, and
 * must be released by using @ref ucp_worker_release_address
 * "ucp_worker_release_address()" routine.
 *
 * @param [in]  worker            Worker object whose address to return.
 * @param [out] address_p         A pointer to the worker address.
 * @param [out] address_length_p  The size in bytes of the address.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_get_address(ucp_worker_h worker,
                                    ucp_address_t **address_p,
                                    size_t *address_length_p);


/**
 * @ingroup UCP_WORKER
 * @brief Release an address of the worker object.
 *
 * This routine release an @ref ucp_address_t "address handle" associated within
 * the @ref ucp_worker_h "worker" object.
 *
 * @warning Once the address released the address handle cannot be used with any
 * UCP routine.
 *
 * @param [in]  worker            Worker object that is associated with the
 *                                address object.
 * @param [in] address            Address to release; the address object has to
 *                                be allocated using @ref ucp_worker_get_address
 *                                "ucp_worker_get_address()" routine.
 *
 * @todo We should consider to change it to return int so we can catch the
 * errors when worker != address
 */
void ucp_worker_release_address(ucp_worker_h worker, ucp_address_t *address);


/**
 * @ingroup UCP_WORKER
 * @brief Progress all communications on a specific worker.
 *
 * This routine explicitly progresses all communication operations on a worker.
 *
 * @note
 * @li Typically, request wait and test routines call @ref
 * ucp_worker_progress "this routine" to progress any outstanding operations.
 * @li Transport layers, implementing asynchronous progress using threads,
 * require callbacks and other user code to be thread safe.
 * @li The state of communication can be advanced (progressed) by blocking
 * routines. Nevertheless, the non-blocking routines can not be used for
 * communication progress.
 *
 * @param [in]  worker    Worker to progress.
 *
 * @return Non-zero if any communication was progressed, zero otherwise.
 */
unsigned ucp_worker_progress(ucp_worker_h worker);


/**
 * @ingroup UCP_WORKER
 * @brief Poll for endpoints that are ready to consume streaming data.
 *
 * This non-blocking routine returns endpoints on a worker which are ready
 * to consume streaming data. The ready endpoints are placed in @a poll_eps
 * array, and the function return value indicates how many are there.
 *
 * @param [in]   worker    Worker to poll.
 * @param [out]  poll_eps  Pointer to array of endpoints, should be
 *                         allocated by user.
 * @param [in]   max_eps   Maximal number of endpoints which should be filled
 *                         in @a poll_eps.
 * @param [in]   flags     Reserved for future use.
 *
 * @return Negative value indicates an error according to @ref ucs_status_t.
 *         On success, non-negative value (less or equal @a max_eps) indicates
 *         actual number of endpoints filled in @a poll_eps array.
 *
 */
ssize_t ucp_stream_worker_poll(ucp_worker_h worker,
                               ucp_stream_poll_ep_t *poll_eps, size_t max_eps,
                               unsigned flags);


/**
 * @ingroup UCP_WAKEUP
 * @brief Obtain an event file descriptor for event notification.
 *
 * This routine returns a valid file descriptor for polling functions.
 * The file descriptor will get signaled when an event occurs, as part of the
 * wake-up mechanism. Signaling means a call to poll() or select() with this
 * file descriptor will return at this point, with this descriptor marked as the
 * reason (or one of the reasons) the function has returned. The user does not
 * need to release the obtained file descriptor.
 *
 * The wake-up mechanism exists to allow for the user process to register for
 * notifications on events of the underlying interfaces, and wait until such
 * occur. This is an alternative to repeated polling for request completion.
 * The goal is to allow for waiting while consuming minimal resources from the
 * system. This is recommended for cases where traffic is infrequent, and
 * latency can be traded for lower resource consumption while waiting for it.
 *
 * There are two alternative ways to use the wakeup mechanism: the first is the
 * file descriptor obtained per worker (this function) and the second is the
 * @ref ucp_worker_wait function for waiting on the next event internally.
 *
 * @note UCP @ref ucp_feature "features" have to be triggered
 *   with @ref UCP_FEATURE_WAKEUP to select proper transport
 *
 * @param [in]  worker    Worker of notified events.
 * @param [out] fd        File descriptor.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_get_efd(ucp_worker_h worker, int *fd);


/**
 * @ingroup UCP_WAKEUP
 * @brief Wait for an event of the worker.
 *
 * This routine waits (blocking) until an event has happened, as part of the
 * wake-up mechanism.
 *
 * This function is guaranteed to return only if new communication events occur
 * on the @a worker. Therefore one must drain all existing events before waiting
 * on the file descriptor. This can be achieved by calling
 * @ref ucp_worker_progress repeatedly until it returns 0.
 *
 * There are two alternative ways to use the wakeup mechanism. The first is by
 * polling on a per-worker file descriptor obtained from @ref ucp_worker_get_efd.
 * The second is by using this function to perform an internal wait for the next
 * event associated with the specified worker.
 *
 * @note During the blocking call the wake-up mechanism relies on other means of
 * notification and may not progress some of the requests as it would when
 * calling @ref ucp_worker_progress (which is not invoked in that duration).
 *
 * @note UCP @ref ucp_feature "features" have to be triggered
 *   with @ref UCP_FEATURE_WAKEUP to select proper transport
 *
 * @param [in]  worker    Worker to wait for events on.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_wait(ucp_worker_h worker);


/**
 * @ingroup UCP_WAKEUP
 * @brief Wait for memory update on the address
 *
 * This routine waits for a memory update at the local memory @a address.  This
 * is a blocking routine. The routine returns when the memory address is
 * updated ("write") or an event occurs in the system.
 *
 * This function is guaranteed to return only if new communication events occur
 * on the worker or @a address is modified. Therefore one must drain all existing
 * events before waiting on the file descriptor. This can be achieved by calling
 * @ref ucp_worker_progress repeatedly until it returns 0.
 *
 * @note This routine can be used by an application that executes busy-waiting
 * loop checking for a memory update. Instead of continuous busy-waiting on an
 * address the application can use @a ucp_worker_wait_mem, which may suspend
 * execution until the memory is updated. The goal of the routine is to provide
 * an opportunity for energy savings for architectures that support this
 * functionality.
 *
 * @param [in] worker           Worker to wait for updates on.
 * @param [in] address          Local memory address
 */
void ucp_worker_wait_mem(ucp_worker_h worker, void *address);


/**
 * @ingroup UCP_WAKEUP
 * @brief Turn on event notification for the next event.
 *
 * This routine needs to be called before waiting on each notification on this
 * worker, so will typically be called once the processing of the previous event
 * is over, as part of the wake-up mechanism.
 *
 * The worker must be armed before waiting on an event (must be re-armed after
 * it has been signaled for re-use) with @ref ucp_worker_arm.
 * The events triggering a signal of the file descriptor from
 * @ref ucp_worker_get_efd depend on the interfaces used by the worker and
 * defined in the transport layer, and typically represent a request completion
 * or newly available resources. It can also be triggered by calling
 * @ref ucp_worker_signal .
 *
 * The file descriptor is guaranteed to become signaled only if new communication
 * events occur on the @a worker. Therefore one must drain all existing events
 * before waiting on the file descriptor. This can be achieved by calling
 * @ref ucp_worker_progress repeatedly until it returns 0.
 *
 * @code {.c}
 * void application_initialization() {
 * // should be called once in application init flow and before
 * // process_comminucation() is used
 *     ...
 *     status = ucp_worker_get_efd(worker, &fd);
 *     ...
 * }
 *
 * void process_comminucation() {
 * // should be called every time need to wait for some condition such as
 * // ucp request completion in sleep mode.
 *
 *     for (;;) {
 *         // check for stop condition as long as progress is made
 *         if (check_for_events()) {
 *              break;
 *         } else if (ucp_worker_progress(worker)) {
 *              continue;                 // some progress happened but condition not met
 *         }
 *
 *         // arm the worker and clean-up fd
 *         status = ucp_worker_arm(worker);
 *         if (UCS_OK == status) {
 *             poll(&fds, nfds, timeout);  // wait for events (sleep mode)
 *         } else if (UCS_ERR_BUSY == status) {
 *             continue;                   // could not arm, need to progress more
 *         } else {
 *             abort();
 *         }
 *     }
 * }
 * @endcode
 *
 * @note UCP @ref ucp_feature "features" have to be triggered
 *   with @ref UCP_FEATURE_WAKEUP to select proper transport
 *
 * @param [in]  worker    Worker of notified events.
 *
 * @return ::UCS_OK        The operation completed successfully. File descriptor
 *                         will be signaled by new events.
 * @return ::UCS_ERR_BUSY  There are unprocessed events which prevent the
 *                         file descriptor from being armed. These events should
 *                         be removed by calling @ref ucp_worker_progress().
 *                         The operation is not completed. File descriptor
 *                         will not be signaled by new events.
 * @return @ref ucs_status_t "Other" different error codes in case of issues.
 */
ucs_status_t ucp_worker_arm(ucp_worker_h worker);


/**
 * @ingroup UCP_WAKEUP
 * @brief Cause an event of the worker.
 *
 * This routine signals that the event has happened, as part of the wake-up
 * mechanism. This function causes a blocking call to @ref ucp_worker_wait or
 * waiting on a file descriptor from @ref ucp_worker_get_efd to return, even
 * if no event from the underlying interfaces has taken place.
 *
 * @note It's safe to use this routine from any thread, even if UCX is compiled
 *       without multi-threading support and/or initialized with any value of
 *       @ref ucp_params_t::mt_workers_shared and
 *       @ref ucp_worker_params_t::thread_mode parameters
 *
 * @param [in]  worker    Worker to wait for events on.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_signal(ucp_worker_h worker);


/**
 * @ingroup UCP_WORKER
 * @brief Accept connections on a local address of the worker object.
 *
 * This routine binds the worker object to a @ref ucs_sock_addr_t sockaddr
 * which is set by the user.
 * The worker will listen to incoming connection requests and upon receiving such
 * a request from the remote peer, an endpoint to it will be created.
 * The user's call-back will be invoked once the endpoint is created.
 *
 * @param [in]  worker           Worker object that is associated with the
 *                               params object.
 * @param [in]  params           User defined @ref ucp_listener_params_t
 *                               configurations for the @ref ucp_listener_h.
 * @param [out] listener_p       A handle to the created listener, can be released
 *                               by calling @ref ucp_listener_destroy
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_listener_create(ucp_worker_h worker,
                                 const ucp_listener_params_t *params,
                                 ucp_listener_h *listener_p);


/**
 * @ingroup UCP_WORKER
 * @brief Stop accepting connections on a local address of the worker object.
 *
 * This routine unbinds the worker from the given handle and stops
 * listening for incoming connection requests on it.
 *
 * @param [in] listener        A handle to the listener to stop listening on.
 */
void ucp_listener_destroy(ucp_listener_h listener);


/**
 * @ingroup UCP_WORKER
 * @brief Get attributes specific to a particular listener.
 *
 * This routine fetches information about the listener.
 *
 * @param [in]  listener   listener object to query.
 * @param [out] attr       Filled with attributes of the listener.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_listener_query(ucp_listener_h listener, ucp_listener_attr_t *attr);


/**
 * @ingroup UCP_WORKER
 * @brief Get attributes specific to a particular connection request received
 * on the server side.
 *
 * This routine fetches information about the connection request.
 *
 * @param [in]  conn_request  connection request object to query.
 * @param [out] attr          Filled with attributes of the connection request.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_conn_request_query(ucp_conn_request_h conn_request,
                                    ucp_conn_request_attr_t *attr);


/**
 * @ingroup UCP_ENDPOINT
 * @brief Create and connect an endpoint.
 *
 * This routine creates and connects an @ref ucp_ep_h "endpoint" on a @ref
 * ucp_worker_h "local worker" for a destination @ref ucp_address_t "address"
 * that identifies the remote @ref ucp_worker_h "worker". This function is
 * non-blocking, and communications may begin immediately after it returns. If
 * the connection process is not completed, communications may be delayed.
 * The created @ref ucp_ep_h "endpoint" is associated with one and only one
 * @ref ucp_worker_h "worker".
 *
 * @param [in]  worker      Handle to the worker; the endpoint
 *                          is associated with the worker.
 * @param [in]  params      User defined @ref ucp_ep_params_t configurations
 *                          for the @ref ucp_ep_h "UCP endpoint".
 * @param [out] ep_p        A handle to the created endpoint.
 *
 * @return Error code as defined by @ref ucs_status_t
 *
 * @note One of the following fields has to be specified:
 *  - ucp_ep_params_t::address
 *  - ucp_ep_params_t::sockaddr
 *  - ucp_ep_params_t::conn_request

 * @note By default, ucp_ep_create() will connect an endpoint to itself if
 * the endpoint is destined to the same @a worker on which it was created,
 * i.e. @a params.address belongs to @a worker. This behavior can be changed by
 * passing the @ref UCP_EP_PARAMS_FLAGS_NO_LOOPBACK flag in @a params.flags.
 * In that case, the endpoint will be connected to the *next* endpoint created
 * in the same way on the same @a worker.
 */
ucs_status_t ucp_ep_create(ucp_worker_h worker, const ucp_ep_params_t *params,
                           ucp_ep_h *ep_p);


/**
 * @ingroup UCP_ENDPOINT
 *
 * @brief Non-blocking @ref ucp_ep_h "endpoint" closure.
 *
 * This routine releases the @ref ucp_ep_h "endpoint". The endpoint closure
 * process depends on the selected @a mode.
 *
 * @param [in]  ep      Handle to the endpoint to close.
 * @param [in]  mode    One from @ref ucp_ep_close_mode value.
 *
 * @return UCS_OK           - The endpoint is closed successfully.
 * @return UCS_PTR_IS_ERR(_ptr) - The closure failed and an error code indicates
 *                                the transport level status. However, resources
 *                                are released and the @a endpoint can no longer
 *                                be used.
 * @return otherwise        - The closure process is started, and can be
 *                            completed at any point in time. A request handle
 *                            is returned to the application in order to track
 *                            progress of the endpoint closure. The application
 *                            is responsible for releasing the handle using the
 *                            @ref ucp_request_free routine.
 *
 * @note @ref ucp_ep_close_nb replaces deprecated @ref ucp_disconnect_nb and
 *       @ref ucp_ep_destroy
 */
ucs_status_ptr_t ucp_ep_close_nb(ucp_ep_h ep, unsigned mode);


/**
 * @ingroup UCP_ENDPOINT
 *
 * @brief Non-blocking @ref ucp_ep_h "endpoint" closure.
 *
 * @param [in]  ep      Handle to the endpoint to close.
 * @param [in]  param   Operation parameters, see @ref ucp_request_param_t.
 *                      This operation supports specific flags, which can be
 *                      passed in @a param by @ref ucp_request_param_t.flags.
 *                      The exact set of flags is defined
 *                      by @ref ucp_ep_close_flags_t.
 *
 * @return NULL                 - The endpoint is closed successfully.
 * @return UCS_PTR_IS_ERR(_ptr) - The closure failed and an error code indicates
 *                                the transport level status. However, resources
 *                                are released and the @a endpoint can no longer
 *                                be used.
 * @return otherwise            - The closure process is started, and can be
 *                                completed at any point in time. A request
 *                                handle is returned to the application in order
 *                                to track progress of the endpoint closure.
 */
ucs_status_ptr_t ucp_ep_close_nbx(ucp_ep_h ep,
                                  const ucp_request_param_t *param);


/**
 * @ingroup UCP_WORKER
 *
 * @brief Reject an incoming connection request.
 *
 * Reject the incoming connection request and release associated resources. If
 * the remote initiator endpoint has set an @ref ucp_ep_params_t::err_handler,
 * it will be invoked with status @ref UCS_ERR_REJECTED.
 *
 * @param [in]  listener        Handle to the listener on which the connection
 *                              request was received.
 * @param [in]  conn_request    Handle to the connection request to reject.
 *
 * @return Error code as defined by @ref ucs_status_t
 *
 */
ucs_status_t ucp_listener_reject(ucp_listener_h listener,
                                 ucp_conn_request_h conn_request);


/**
 * @ingroup UCP_ENDPOINT
 * @brief Print endpoint information.
 *
 * This routine prints information about the endpoint transport methods, their
 * thresholds, and other useful information associated with the endpoint.
 *
 * @param [in] ep           Endpoint object whose configuration to print.
 * @param [in] stream       Output stream to print the information to.
 */
void ucp_ep_print_info(ucp_ep_h ep, FILE *stream);


/**
 * @ingroup UCP_ENDPOINT
 *
 * @brief Non-blocking flush of outstanding AMO and RMA operations on the
 * @ref ucp_ep_h "endpoint".
 *
 * This routine flushes all outstanding AMO and RMA communications on the
 * @ref ucp_ep_h "endpoint". All the AMO and RMA operations issued on the
 * @a ep prior to this call are completed both at the origin and at the target
 * @ref ucp_ep_h "endpoint" when this call returns.
 *
 * @param [in] ep        UCP endpoint.
 * @param [in] flags     Flags for flush operation. Reserved for future use.
 * @param [in] cb        Callback which will be called when the flush operation
 *                       completes.
 *
 * @return NULL             - The flush operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The flush operation failed.
 * @return otherwise        - Flush operation was scheduled and can be completed
 *                          in any point in time. The request handle is returned
 *                          to the application in order to track progress. The
 *                          application is responsible for releasing the handle
 *                          using @ref ucp_request_free "ucp_request_free()"
 *                          routine.
 *
 *
 * The following example demonstrates how blocking flush can be implemented
 * using non-blocking flush:
 * @code {.c}
 * void empty_function(void *request, ucs_status_t status)
 * {
 * }
 *
 * ucs_status_t blocking_ep_flush(ucp_ep_h ep, ucp_worker_h worker)
 * {
 *     void *request;
 *
 *     request = ucp_ep_flush_nb(ep, 0, empty_function);
 *     if (request == NULL) {
 *         return UCS_OK;
 *     } else if (UCS_PTR_IS_ERR(request)) {
 *         return UCS_PTR_STATUS(request);
 *     } else {
 *         ucs_status_t status;
 *         do {
 *             ucp_worker_progress(worker);
 *             status = ucp_request_check_status(request);
 *         } while (status == UCS_INPROGRESS);
 *         ucp_request_free(request);
 *         return status;
 *     }
 * }
 * @endcode */
ucs_status_ptr_t ucp_ep_flush_nb(ucp_ep_h ep, unsigned flags,
                                 ucp_send_callback_t cb);


/**
 * @ingroup UCP_ENDPOINT
 *
 * @brief Non-blocking flush of outstanding AMO and RMA operations on the
 * @ref ucp_ep_h "endpoint".
 *
 * This routine flushes all outstanding AMO and RMA communications on the
 * @ref ucp_ep_h "endpoint". All the AMO and RMA operations issued on the
 * @a ep prior to this call are completed both at the origin and at the target
 * @ref ucp_ep_h "endpoint" when this call returns.
 *
 * @param [in] ep        UCP endpoint.
 * @param [in] param     Operation parameters, see @ref ucp_request_param_t.
 *
 * @return NULL                 - The flush operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The flush operation failed.
 * @return otherwise            - Flush operation was scheduled and can be
 *                                completed in any point in time. The request
 *                                handle is returned to the application in
 *                                order to track progress.
 */
ucs_status_ptr_t ucp_ep_flush_nbx(ucp_ep_h ep, const ucp_request_param_t *param);


/**
 * @ingroup UCP_MEM
 * @brief Map or allocate memory for zero-copy operations.
 *
 * This routine maps or/and allocates a user-specified memory segment with @ref
 * ucp_context_h "UCP application context" and the network resources associated
 * with it. If the application specifies NULL as an address for the memory
 * segment, the routine allocates a mapped memory segment and returns its
 * address in the @a address_p argument.  The network stack associated with an
 * application context can typically send and receive data from the mapped
 * memory without CPU intervention; some devices and associated network stacks
 * require the memory to be mapped to send and receive data. The @ref ucp_mem_h
 * "memory handle" includes all information required to access the memory
 * locally using UCP routines, while @ref ucp_rkey_h
 * "remote registration handle" provides an information that is necessary for
 * remote memory access.
 *
 * @note
 * Another well know terminology for the "map" operation that is typically
 * used in the context of networking is memory "registration" or "pinning". The
 * UCP library registers the memory the available hardware so it can be
 * assessed directly by the hardware.
 *
 * Memory mapping assumptions:
 * @li A given memory segment can be mapped by several different communication
 * stacks, if these are compatible.
 * @li The @a memh_p handle returned may be used with any sub-region of the
 * mapped memory.
 * @li If a large segment is registered, and then segmented for subsequent use
 * by a user, then the user is responsible for segmentation and subsequent
 * management.
 *
 * <table>
 * <caption>Matrix of behavior</caption>
 * <tr><th>parameter/flag <td align="center">@ref UCP_MEM_MAP_NONBLOCK "NONBLOCK"</td>
 *                        <td align="center">@ref UCP_MEM_MAP_ALLOCATE "ALLOCATE"</td>
 *                        <td align="center">@ref UCP_MEM_MAP_FIXED "FIXED"</td>
 *                        <td align="center">@ref ucp_mem_map_params.address "address"</td>
 *                        <td align="center">@b result
 * <tr><td rowspan="8" align="center">@b value <td rowspan="8" align="center">0/1 - the value\n only affects the\n register/map\n phase</td>
 *                                               <td align="center">0 <td align="center">0 <td align="center">0 <td align="center">@ref anch_err "error" if length > 0
 * <tr>                                          <td align="center">1 <td align="center">0 <td align="center">0 <td align="center">@ref anch_alloc_reg "alloc+register"
 * <tr>                                          <td align="center">0 <td align="center">1 <td align="center">0 <td align="center">@ref anch_err "error"</td>
 * <tr>                                          <td align="center">0 <td align="center">0 <td align="center">defined <td align="center">@ref anch_reg "register"
 * <tr>                                          <td align="center">1 <td align="center">1 <td align="center">0 <td align="center">@ref anch_err "error"</td>
 * <tr>                                          <td align="center">1 <td align="center">0 <td align="center">defined <td align="center">@ref anch_alloc_hint_reg "alloc+register,hint"
 * <tr>                                          <td align="center">0 <td align="center">1 <td align="center">defined <td align="center">@ref anch_err "error"</td>
 * <tr>                                          <td align="center">1 <td align="center">1 <td align="center">defined <td align="center">@ref anch_alloc_fixed_reg "alloc+register,fixed"
 * </table>
 *
 * @note
 * @li \anchor anch_reg @b register means that the memory will be registered in
 *     corresponding transports for RMA/AMO operations. This case intends that
 *     the memory was allocated by user before.
 * @li \anchor anch_alloc_reg @b alloc+register means that the memory will be allocated
 *     in the memory provided by the system and registered in corresponding
 *     transports for RMA/AMO operations.
 * @li \anchor anch_alloc_hint_reg <b>alloc+register,hint</b> means that
 *     the memory will be allocated with using @ref ucp_mem_map_params.address
 *     as a hint and registered in corresponding transports for RMA/AMO operations.
 * @li \anchor anch_alloc_fixed_reg <b>alloc+register,fixed</b> means that the memory
 *     will be allocated and registered in corresponding transports for RMA/AMO
 *     operations.
 * @li \anchor anch_err @b error is an erroneous combination of the parameters.
 *
 * @param [in]     context    Application @ref ucp_context_h "context" to map
 *                            (register) and allocate the memory on.
 * @param [in]     params     User defined @ref ucp_mem_map_params_t configurations
 *                            for the @ref ucp_mem_h "UCP memory handle".
 * @param [out]    memh_p     UCP @ref ucp_mem_h "handle" for the allocated
 *                            segment.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_mem_map(ucp_context_h context, const ucp_mem_map_params_t *params,
                         ucp_mem_h *memh_p);


/**
 * @ingroup UCP_MEM
 * @brief Unmap memory segment
 *
 * This routine unmaps a user specified memory segment, that was previously
 * mapped using the @ref ucp_mem_map "ucp_mem_map()" routine.  The unmap
 * routine will also release the resources associated with the memory
 * @ref ucp_mem_h "handle".  When the function returns, the @ref ucp_mem_h
 * and associated @ref ucp_rkey_h "remote key" will be invalid and cannot be
 * used with any UCP routine.
 *
 * @note
 * Another well know terminology for the "unmap" operation that is typically
 * used in the context of networking is memory "de-registration". The UCP
 * library de-registers the memory the available hardware so it can be returned
 * back to the operation system.
 *
 * Error cases:
 * @li Once memory is unmapped a network access to the region may cause a
 * failure.
 *
 * @param [in]  context     Application @ref ucp_context_h "context" which was
 *                          used to allocate/map the memory.
 * @param [in]  memh        @ref ucp_mem_h "Handle" to memory region.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_mem_unmap(ucp_context_h context, ucp_mem_h memh);


/**
 * @ingroup UCP_MEM
 * @brief query mapped memory segment
 *
 * This routine returns address and length of memory segment mapped with
 * @ref ucp_mem_map "ucp_mem_map()" routine.
 *
 * @param [in]  memh    @ref ucp_mem_h "Handle" to memory region.
 * @param [out] attr    Filled with attributes of the @ref ucp_mem_h
 *                      "UCP memory handle".
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_mem_query(const ucp_mem_h memh, ucp_mem_attr_t *attr);


/**
 * @ingroup UCP_MEM
 * @brief Print memory mapping information.
 *
 * This routine maps memory and prints information about the created memory handle:
 * including the mapped memory length, the allocation method, and other useful
 * information associated with the memory handle.
 *
 * @param [in] mem_size     Size of the memory to map.
 * @param [in] context      The context on which the memory is mapped.
 * @param [in] stream       Output stream on which to print the information.
 */
void ucp_mem_print_info(const char *mem_size, ucp_context_h context, FILE *stream);


/**
 * @ingroup UCP_MEM
 * @brief list of UCP memory use advice.
 *
 * The enumeration list describes memory advice supported by @ref
 * ucp_mem_advise() function.
 */
typedef enum ucp_mem_advice {
    UCP_MADV_NORMAL   = 0,  /**< No special treatment */
    UCP_MADV_WILLNEED       /**< can be used on the memory mapped with
                                 @ref UCP_MEM_MAP_NONBLOCK to speed up memory
                                 mapping and to avoid page faults when
                                 the memory is accessed for the first time. */
} ucp_mem_advice_t;


/**
 * @ingroup UCP_MEM
 * @brief Tuning parameters for the UCP memory advice.
 *
 * This structure defines the parameters that are used for the
 * UCP memory advice tuning during the @ref ucp_mem_advise "ucp_mem_advise"
 * routine.
 */
typedef struct ucp_mem_advise_params {
    /**
     * Mask of valid fields in this structure, using bits from
     * @ref ucp_mem_advise_params_field. All fields are mandatory.
     * Provides ABI compatibility with respect to adding new fields.
     */
    uint64_t                field_mask;

    /**
     * Memory base address.
     */
     void                   *address;

     /**
      * Length (in bytes) to allocate or map (register).
      */
     size_t                 length;

     /**
      * Memory use advice @ref ucp_mem_advice
      */
     ucp_mem_advice_t       advice;
} ucp_mem_advise_params_t;


/**
 * @ingroup UCP_MEM
 * @brief give advice about the use of memory
 *
 * This routine advises the UCP about how to handle memory range beginning at
 * address and size of length bytes. This call does not influence the semantics
 * of the application, but may influence its performance. The UCP may ignore
 * the advice.
 *
 * @param [in]  context     Application @ref ucp_context_h "context" which was
 *                          used to allocate/map the memory.
 * @param [in]  memh        @ref ucp_mem_h "Handle" to memory region.
 * @param [in]  params      Memory base address and length. The advice field
 *                          is used to pass memory use advice as defined in
 *                          the @ref ucp_mem_advice list
 *                          The memory range must belong to the @a memh
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_mem_advise(ucp_context_h context, ucp_mem_h memh,
                            ucp_mem_advise_params_t *params);


/**
 * @ingroup UCP_MEM
 * @brief Pack memory region remote access key.
 *
 * This routine allocates memory buffer and packs into the buffer
 * a remote access key (RKEY) object. RKEY is an opaque object that provides
 * the information that is necessary for remote memory access.
 * This routine packs the RKEY object in a portable format such that the
 * object can be @ref ucp_ep_rkey_unpack "unpacked" on any platform supported by the
 * UCP library. In order to release the memory buffer allocated by this routine
 * the application is responsible for calling the @ref ucp_rkey_buffer_release
 * "ucp_rkey_buffer_release()" routine.
 *
 *
 * @note
 * @li RKEYs for InfiniBand and Cray Aries networks typically includes
 * InifiniBand and Aries key.
 * @li In order to enable remote direct memory access to the memory associated
 * with the memory handle the application is responsible for sharing the RKEY with
 * the peers that will initiate the access.
 *
 * @param [in]  context       Application @ref ucp_context_h "context" which was
 *                            used to allocate/map the memory.
 * @param [in]  memh          @ref ucp_mem_h "Handle" to memory region.
 * @param [out] rkey_buffer_p Memory buffer allocated by the library.
 *                            The buffer contains packed RKEY.
 * @param [out] size_p        Size (in bytes) of the packed RKEY.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_rkey_pack(ucp_context_h context, ucp_mem_h memh,
                           void **rkey_buffer_p, size_t *size_p);


/**
 * @ingroup UCP_MEM
 * @brief Release packed remote key buffer.
 *
 * This routine releases the buffer that was allocated using @ref ucp_rkey_pack
 * "ucp_rkey_pack()".
 *
 * @warning
 * @li Once memory is released an access to the memory may cause a
 * failure.
 * @li If the input memory address was not allocated using
 * @ref ucp_rkey_pack "ucp_rkey_pack()" routine the behaviour of this routine
 * is undefined.
 *
 * @param [in]  rkey_buffer   Buffer to release.
 */
void ucp_rkey_buffer_release(void *rkey_buffer);


/**
 * @ingroup UCP_MEM
 * @brief Create remote access key from packed buffer.
 *
 * This routine unpacks the remote key (RKEY) object into the local memory
 * such that it can be accessed and used by UCP routines. The RKEY object has
 * to be packed using the @ref ucp_rkey_pack "ucp_rkey_pack()" routine.
 * Application code should not make any changes to the content of the RKEY
 * buffer.
 *
 * @note The application is responsible for releasing the RKEY object when
 *       it is no longer needed, by calling the @ref ucp_rkey_destroy
 *       "ucp_rkey_destroy()" routine.
 * @note The remote key object can be used for communications only on the
 *       endpoint on which it was unpacked.
 *
 * @param [in]  ep            Endpoint to access using the remote key.
 * @param [in]  rkey_buffer   Packed rkey.
 * @param [out] rkey_p        Remote key handle.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_ep_rkey_unpack(ucp_ep_h ep, const void *rkey_buffer,
                                ucp_rkey_h *rkey_p);


/**
 * @ingroup UCP_MEM
 * @brief Get a local pointer to remote memory.
 *
 * This routine returns a local pointer to the remote memory described
 * by the rkey.
 *
 * @note This routine can return a valid pointer only for the endpoints
 * that are reachable via shared memory.
 *
 * @param [in]  rkey          A remote key handle.
 * @param [in]  raddr         A remote memory address within the memory area
 *                            described by the rkey.
 * @param [out] addr_p        A pointer that can be used for direct
 *                            access to the remote memory.
 *
 * @return Error code as defined by @ref ucs_status_t if the remote memory
 *         cannot be accessed directly or the remote memory address is not valid.
 */
ucs_status_t ucp_rkey_ptr(ucp_rkey_h rkey, uint64_t raddr, void **addr_p);


/**
 * @ingroup UCP_MEM
 * @brief Destroy the remote key
 *
 * This routine destroys the RKEY object and the memory that was allocated
 * using the @ref ucp_ep_rkey_unpack "ucp_ep_rkey_unpack()" routine. This
 * routine also releases any resources that are associated with the RKEY
 * object.
 *
 * @warning
 * @li Once the RKEY object is released an access to the memory will cause an
 * undefined failure.
 * @li If the RKEY object was not created using
 * @ref ucp_ep_rkey_unpack "ucp_ep_rkey_unpack()" routine the behavior of this
 * routine is undefined.
 * @li The RKEY object must be destroyed after all outstanding operations which
 * are using it are flushed, and before the endpoint on which it was unpacked
 * is destroyed.
 *
 * @param [in]  rkey         Remote key to destroy.
 */
void ucp_rkey_destroy(ucp_rkey_h rkey);


/**
 * @ingroup UCP_WORKER
 * @brief Add user defined callback for Active Message.
 *
 * This routine installs a user defined callback to handle incoming Active
 * Messages with a specific id. This callback is called whenever an Active 
 * Message that was sent from the remote peer by @ref ucp_am_send_nb is 
 * received on this worker.
 *
 * @param [in]  worker      UCP worker on which to set the Active Message 
 *                          handler.
 * @param [in]  id          Active Message id.
 * @param [in]  cb          Active Message callback. NULL to clear.
 * @param [in]  arg         Active Message argument, which will be passed
 *                          in to every invocation of the callback as the
 *                          arg argument.
 * @param [in]  flags       Dictates how an Active Message is handled on the
 *                          remote endpoint. Currently only
 *                          UCP_AM_FLAG_WHOLE_MSG is supported, which
 *                          indicates the callback will not be invoked
 *                          until all data has arrived.
 *
 * @return error code if the worker does not support Active Messages or
 *         requested callback flags.
 */
ucs_status_t ucp_worker_set_am_handler(ucp_worker_h worker, uint16_t id,
                                       ucp_am_callback_t cb, void *arg,
                                       uint32_t flags);


/**
 * @ingroup UCP_WORKER
 * @brief Add user defined callback for Active Message.
 *
 * This routine installs a user defined callback to handle incoming Active
 * Messages with a specific id. This callback is called whenever an Active
 * Message that was sent from the remote peer by @ref ucp_am_send_nbx is
 * received on this worker.
 *
 * @warning Handlers set by this function are not compatible with
            @ref ucp_am_send_nb routine.
 *
 * @param [in]  worker      UCP worker on which to set the Active Message
 *                          handler.
 * @param [in]  param       Active Message handler parameters, as defined by
 *                          @ref ucp_am_handler_param_t.
 *
 * @return error code if the worker does not support Active Messages or
 *         requested callback flags.
 */
ucs_status_t ucp_worker_set_am_recv_handler(ucp_worker_h worker,
                                            const ucp_am_handler_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Send Active Message.
 *
 * This routine sends an Active Message to an ep. It does not support
 * CUDA memory.
 *
 * @param [in]  ep          UCP endpoint where the Active Message will be run.
 * @param [in]  id          Active Message id. Specifies which registered
 *                          callback to run.
 * @param [in]  buffer      Pointer to the data to be sent to the target node
 *                          of the Active Message.
 * @param [in]  count       Number of elements to send.
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  cb          Callback that is invoked upon completion of the
 *                          data transfer if it is not completed immediately.
 * @param [in]  flags       Operation flags as defined by @ref ucp_send_am_flags.
 *
 * @return NULL             Active Message was sent immediately.
 * @return UCS_PTR_IS_ERR(_ptr) Error sending Active Message.
 * @return otherwise        Pointer to request, and Active Message is known
 *                          to be completed after cb is run.
 */
ucs_status_ptr_t ucp_am_send_nb(ucp_ep_h ep, uint16_t id,
                                const void *buffer, size_t count,
                                ucp_datatype_t datatype,
                                ucp_send_callback_t cb, unsigned flags);


/**
 * @ingroup UCP_COMM
 * @brief Send Active Message.
 *
 * This routine sends an Active Message to an ep. If the operation completes
 * immediately, then the routine returns NULL and the callback function is
 * ignored, even if specified. Otherwise, if no error is reported and a callback
 * is requested (i.e. the UCP_OP_ATTR_FIELD_CALLBACK flag is set in the
 * op_attr_mask field of @a param), then the UCP library will schedule
 * invocation of the callback routine @a param->cb.send upon completion of the
 * operation.
 *
 * @note If UCP_OP_ATTR_FLAG_NO_IMM_CMPL flag is set in the op_attr_mask field
 *       of @a param, then the operation will return a request handle, even if
 *       it completes immediately.
 * @note Currently Active Message API supports communication operations with
 *       host memory only.
 * @note This operation supports specific flags, which can be passed
 *       in @a param by @ref ucp_request_param_t.flags. The exact set of flags
 *       is defined by @ref ucp_send_am_flags.
 *
 * @param [in]  ep            UCP endpoint where the Active Message will be run.
 * @param [in]  id            Active Message id. Specifies which registered
 *                            callback to run.
 * @param [in]  header        User defined Active Message header. NULL value is
 *                            allowed if no header needed. In this case
 *                            @a header_length should be set to 0.
 * @param [in]  header_length Active message header length in bytes.
 * @param [in]  buffer        Pointer to the data to be sent to the target node
 *                            of the Active Message.
 * @param [in]  count         Number of elements to send.
 * @param [in]  param         Operation parameters, see @ref ucp_request_param_t.
 *
 * @note Sending only header without actual data is allowed and is recommended
 *       for transfering latency-critical amount of data.
 * @note The maximum allowed header size can be obtained by querying worker
 *       attributes by @ref ucp_worker_query routine.
 *
 *
 * @return NULL                 - Active Message was sent immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - Error sending Active Message.
 * @return otherwise            - Operation was scheduled for send and can be
 *                                completed at any point in time. The request
 *                                handle is returned to the application in order
 *                                to track progress of the message. If user
 *                                request was not provided in @a param->request,
 *                                the application is responsible for releasing
 *                                the handle using @ref ucp_request_free routine.
 */
ucs_status_ptr_t ucp_am_send_nbx(ucp_ep_h ep, unsigned id,
                                 const void *header, size_t header_length,
                                 const void *buffer, size_t count,
                                 const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Receive Active Message sent with rendezvous protocol.
 *
 * This routine receives a message that is described by the data descriptor
 * @a data_desc, local address @a buffer, size @a count and @a param
 * parameters on the @a worker. The routine is non-blocking and therefore
 * returns immediately. The receive operation is considered completed when the
 * message is delivered to the @a buffer. If the receive operation cannot be
 * started the routine returns an error.
 *
 * @note After this call UCP takes ownership of @a data_desc descriptor, so
 *       there is no need to release it even if the operation fails.
 *       The routine returns a request handle instead, which can further be used
 *       for tracking operation progress.
 *
 * @note Currently Active Message API supports communication operations with
 *       host memory only.
 *
 * @param [in]  worker     Worker that is used for the receive operation.
 * @param [in]  data_desc  Data descriptor, provided in
                           @ref ucp_am_recv_callback_t routine.
 * @param [in]  buffer     Pointer to the buffer to receive the data.
 * @param [in]  count      Number of elements to receive into @a buffer.
 * @param [in]  param      Operation parameters, see @ref ucp_request_param_t.
 *
 * @return NULL                 - The receive operation was completed
 *                                immediately. In this case, if
 *                                @a param->recv_info.length is specified in the
 *                                @a param, the value to which it points is updated
 *                                with the size of the received message.
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise            - Receive operation was scheduled and can be
 *                                completed at any point in time. The request
 *                                handle is returned to the application in order
 *                                to track operation progress. If user
 *                                request was not provided in @a param->request,
 *                                the application is responsible for releasing
 *                                the handle using @ref ucp_request_free routine.
 */
ucs_status_ptr_t ucp_am_recv_data_nbx(ucp_worker_h worker, void *data_desc,
                                      void *buffer, size_t count,
                                      const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Releases Active Message data.
 *
 * This routine releases data that persisted through an Active Message
 * callback because that callback returned UCS_INPROGRESS.
 *
 * @param [in] worker       Worker which received the Active Message.
 * @param [in] data         Pointer to data that was passed into
 *                          the Active Message callback as the data
 *                          parameter.
 */
void ucp_am_data_release(ucp_worker_h worker, void *data);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking stream send operation.
 *
 * This routine sends data that is described by the local address @a buffer,
 * size @a count, and @a datatype object to the destination endpoint @a ep.
 * The routine is non-blocking and therefore returns immediately, however
 * the actual send operation may be delayed. The send operation is considered
 * completed when it is safe to reuse the source @e buffer. If the send
 * operation is completed immediately the routine returns UCS_OK and the
 * callback function @a cb is @b not invoked. If the operation is
 * @b not completed immediately and no error reported, then the UCP library will
 * schedule invocation of the callback @a cb upon completion of the send
 * operation. In other words, the completion of the operation will be signaled
 * either by the return code or by the callback.
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send.
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  cb          Callback function that is invoked whenever the
 *                          send operation is completed. It is important to note
 *                          that the callback is only invoked in the event that
 *                          the operation cannot be completed in place.
 * @param [in]  flags       Reserved for future use.
 *
 * @return NULL             - The send operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The send operation failed.
 * @return otherwise        - Operation was scheduled for send and can be
 *                          completed in any point in time. The request handle
 *                          is returned to the application in order to track
 *                          progress of the message. The application is
 *                          responsible for releasing the handle using
 *                          @ref ucp_request_free routine.
 */
ucs_status_ptr_t ucp_stream_send_nb(ucp_ep_h ep, const void *buffer, size_t count,
                                    ucp_datatype_t datatype, ucp_send_callback_t cb,
                                    unsigned flags);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking stream send operation.
 *
 * This routine sends data that is described by the local address @a buffer,
 * size @a count object to the destination endpoint @a ep. The routine is
 * non-blocking and therefore returns immediately, however the actual send
 * operation may be delayed. The send operation is considered completed when
 * it is safe to reuse the source @e buffer. If the send operation is
 * completed immediately the routine returns UCS_OK.
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send.
 * @param [in]  param       Operation parameters, see @ref ucp_request_param_t.
 *
 * @return NULL                 - The send operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The send operation failed.
 * @return otherwise            - Operation was scheduled for send and can be
 *                                completed at any point in time. The request
 *                                handle is returned to the application in
 *                                order to track progress of the message.
 */
ucs_status_ptr_t ucp_stream_send_nbx(ucp_ep_h ep, const void *buffer, size_t count,
                                     const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking tagged-send operations
 *
 * This routine sends a messages that is described by the local address @a
 * buffer, size @a count, and @a datatype object to the destination endpoint
 * @a ep. Each message is associated with a @a tag value that is used for
 * message matching on the @ref ucp_tag_recv_nb "receiver". The routine is
 * non-blocking and therefore returns immediately, however the actual send
 * operation may be delayed. The send operation is considered completed when
 * it is safe to reuse the source @e buffer. If the send operation is
 * completed immediately the routine return UCS_OK and the call-back function
 * @a cb is @b not invoked. If the operation is @b not completed immediately
 * and no error reported then the UCP library will schedule to invoke the
 * call-back @a cb whenever the send operation will be completed. In other
 * words, the completion of a message can be signaled by the return code or
 * the call-back.
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  tag         Message tag.
 * @param [in]  cb          Callback function that is invoked whenever the
 *                          send operation is completed. It is important to note
 *                          that the call-back is only invoked in a case when
 *                          the operation cannot be completed in place.
 *
 * @return NULL            - The send operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The send operation failed.
 * @return otherwise        - Operation was scheduled for send and can be
 *                          completed in any point in time. The request handle
 *                          is returned to the application in order to track
 *                          progress of the message. The application is
 *                          responsible for releasing the handle using
 *                          @ref ucp_request_free "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_tag_send_nb(ucp_ep_h ep, const void *buffer, size_t count,
                                 ucp_datatype_t datatype, ucp_tag_t tag,
                                 ucp_send_callback_t cb);

/**
 * @ingroup UCP_COMM
 * @brief Non-blocking tagged-send operations with user provided request
 *
 * This routine provides a convenient and efficient way to implement a
 * blocking send pattern. It also completes requests faster than
 * @ref ucp_tag_send_nb() because:
 * @li it always uses @ref uct_ep_am_bcopy() to send data up to the
 *     rendezvous threshold.
 * @li its rendezvous threshold is higher than the one used by
 *     the @ref ucp_tag_send_nb(). The threshold is controlled by
 *     the @b UCX_SEND_NBR_RNDV_THRESH environment variable.
 * @li its request handling is simpler. There is no callback and no need
 *     to allocate and free requests. In fact request can be allocated by
 *     caller on the stack.
 *
 * This routine sends a messages that is described by the local address @a
 * buffer, size @a count, and @a datatype object to the destination endpoint
 * @a ep. Each message is associated with a @a tag value that is used for
 * message matching on the @ref ucp_tag_recv_nbr "receiver".
 *
 * The routine is non-blocking and therefore returns immediately, however
 * the actual send operation may be delayed. The send operation is considered
 * completed when it is safe to reuse the source @e buffer. If the send
 * operation is completed immediately the routine returns UCS_OK.
 *
 * If the operation is @b not completed immediately and no error reported
 * then the UCP library will fill a user provided @a req and
 * return UCS_INPROGRESS status. In order to monitor completion of the
 * operation @ref ucp_request_check_status() should be used.
 *
 * Following pseudo code implements a blocking send function:
 * @code
 * MPI_send(...)
 * {
 *     char *request;
 *     ucs_status_t status;
 *
 *     // allocate request on the stack
 *     // ucp_context_query() was used to get ucp_request_size
 *     request = alloca(ucp_request_size);
 *
 *     // note: make sure that there is enough memory before the
 *     // request handle
 *     status = ucp_tag_send_nbr(ep, ..., request + ucp_request_size);
 *     if (status != UCS_INPROGRESS) {
 *         return status;
 *     }
 *
 *     do {
 *         ucp_worker_progress(worker);
 *         status = ucp_request_check_status(request + ucp_request_size);
 *     } while (status == UCS_INPROGRESS);
 *
 *     return status;
 * }
 * @endcode
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 *
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  tag         Message tag.
 * @param [in]  req         Request handle allocated by the user. There should
 *                          be at least UCP request size bytes of available
 *                          space before the @a req. The size of UCP request
 *                          can be obtained by @ref ucp_context_query function.
 *
 * @return UCS_OK           - The send operation was completed immediately.
 * @return UCS_INPROGRESS   - The send was not completed and is in progress.
 *                            @ref ucp_request_check_status() should be used to
 *                            monitor @a req status.
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_tag_send_nbr(ucp_ep_h ep, const void *buffer, size_t count,
                              ucp_datatype_t datatype, ucp_tag_t tag, void *req);

/**
 * @ingroup UCP_COMM
 * @brief Non-blocking synchronous tagged-send operation.
 *
 * Same as @ref ucp_tag_send_nb, except the request completes only after there
 * is a remote tag match on the message (which does not always mean the remote
 * receive has been completed). This function never completes "in-place", and
 * always returns a request handle.
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 * @note Returns @ref UCS_ERR_UNSUPPORTED if @ref UCP_ERR_HANDLING_MODE_PEER is
 *       enabled. This is a temporary implementation-related constraint that
 *       will be addressed in future releases.
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  tag         Message tag.
 * @param [in]  cb          Callback function that is invoked whenever the
 *                          send operation is completed.
 *
 * @return UCS_PTR_IS_ERR(_ptr) - The send operation failed.
 * @return otherwise        - Operation was scheduled for send and can be
 *                          completed in any point in time. The request handle
 *                          is returned to the application in order to track
 *                          progress of the message. The application is
 *                          responsible for releasing the handle using
 *                          @ref ucp_request_free "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_tag_send_sync_nb(ucp_ep_h ep, const void *buffer, size_t count,
                                      ucp_datatype_t datatype, ucp_tag_t tag,
                                      ucp_send_callback_t cb);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking tagged-send operation
 *
 * This routine sends a messages that is described by the local address @a
 * buffer, size @a count object to the destination endpoint @a ep. Each
 * message is associated with a @a tag value that is used for message
 * matching on the @ref ucp_tag_recv_nb or @ref ucp_tag_recv_nbx "receiver".
 * The routine is non-blocking and therefore returns immediately, however the
 * actual send operation may be delayed. The send operation is considered
 * completed when it is safe to reuse the source @e buffer. If the send
 * operation is completed immediately the routine returns UCS_OK and the
 * call-back function is @b not invoked. If the operation is @b not completed
 * immediately and no error reported then the UCP library will schedule to
 * invoke the call-back whenever the send operation is completed. In other
 * words, the completion of a message can be signaled by the return code or
 * the call-back.
 * Immediate completion signals can be fine-tuned via the
 * @ref ucp_request_param_t.op_attr_mask field in the
 * @ref ucp_request_param_t structure. The values of this field
 * are a bit-wise OR of the @ref ucp_op_attr_t enumeration.
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send
 * @param [in]  tag         Message tag.
 * @param [in]  param       Operation parameters, see @ref ucp_request_param_t
 *
 * @return UCS_OK               - The send operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The send operation failed.
 * @return otherwise            - Operation was scheduled for send and can be
 *                                completed in any point in time. The request handle
 *                                is returned to the application in order to track
 *                                progress of the message.
 */
ucs_status_ptr_t ucp_tag_send_nbx(ucp_ep_h ep, const void *buffer, size_t count,
                                  ucp_tag_t tag, const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking synchronous tagged-send operation.
 *
 * Same as @ref ucp_tag_send_nbx, except the request completes only after there
 * is a remote tag match on the message (which does not always mean the remote
 * receive has been completed). This function never completes "in-place", and
 * always returns a request handle.
 *
 * @note The user should not modify any part of the @a buffer after this
 *       operation is called, until the operation completes.
 * @note Returns @ref UCS_ERR_UNSUPPORTED if @ref UCP_ERR_HANDLING_MODE_PEER is
 *       enabled. This is a temporary implementation-related constraint that
 *       will be addressed in future releases.
 *
 * @param [in]  ep          Destination endpoint handle.
 * @param [in]  buffer      Pointer to the message buffer (payload).
 * @param [in]  count       Number of elements to send
 * @param [in]  tag         Message tag.
 * @param [in]  param       Operation parameters, see @ref ucp_request_param_t
 *
 * @return UCS_OK               - The send operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The send operation failed.
 * @return otherwise            - Operation was scheduled for send and can be
 *                                completed in any point in time. The request handle
 *                                is returned to the application in order to track
 *                                progress of the message.
 */
ucs_status_ptr_t ucp_tag_send_sync_nbx(ucp_ep_h ep, const void *buffer,
                                       size_t count, ucp_tag_t tag,
                                       const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking stream receive operation of structured data into a
 *        user-supplied buffer.
 *
 * This routine receives data that is described by the local address @a buffer,
 * size @a count, and @a datatype object on the endpoint @a ep. The routine is
 * non-blocking and therefore returns immediately. The receive operation is
 * considered complete when the message is delivered to the buffer. If data is
 * not immediately available, the operation will be scheduled for receive and
 * a request handle will be returned. In order to notify the application about
 * completion of a scheduled receive operation, the UCP library will invoke
 * the call-back @a cb when data is in the receive buffer and ready for
 * application access. If the receive operation cannot be started, the routine
 * returns an error.
 *
 * @param [in]     ep       UCP endpoint that is used for the receive operation.
 * @param [in]     buffer   Pointer to the buffer to receive the data to.
 * @param [in]     count    Number of elements to receive into @a buffer.
 * @param [in]     datatype Datatype descriptor for the elements in the buffer.
 * @param [in]     cb       Callback function that is invoked whenever the
 *                          receive operation is completed and the data is ready
 *                          in the receive @a buffer. It is important to note
 *                          that the call-back is only invoked in a case when
 *                          the operation cannot be completed immediately.
 * @param [out]    length   Size of the received data in bytes. The value is
 *                          valid only if return code is UCS_OK.
 * @note                    The amount of data received, in bytes, is always an
 *                          integral multiple of the @a datatype size.
 * @param [in]     flags    Flags defined in @ref ucp_stream_recv_flags_t.
 *
 * @return NULL                 - The receive operation was completed
 *                                immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise            - Operation was scheduled for receive. A request
 *                                handle is returned to the application in order
 *                                to track progress of the operation.
 *                                The application is responsible for releasing
 *                                the handle by calling the
 *                                @ref ucp_request_free routine.
 */
ucs_status_ptr_t ucp_stream_recv_nb(ucp_ep_h ep, void *buffer, size_t count,
                                    ucp_datatype_t datatype,
                                    ucp_stream_recv_callback_t cb,
                                    size_t *length, unsigned flags);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking stream receive operation of structured data into a
 *        user-supplied buffer.
 *
 * This routine receives data that is described by the local address @a buffer,
 * size @a count object on the endpoint @a ep. The routine is non-blocking
 * and therefore returns immediately. The receive operation is considered
 * complete when the message is delivered to the buffer. If the receive
 * operation cannot be started, the routine returns an error.
 *
 * @param [in]     ep       UCP endpoint that is used for the receive operation.
 * @param [in]     buffer   Pointer to the buffer that will receive the data.
 * @param [in]     count    Number of elements to receive into @a buffer.
 * @param [out]    length   Size of the received data in bytes. The value is
 *                          valid only if return code is NULL.
 * @param [in]     param    Operation parameters, see @ref ucp_request_param_t.
 *                          This operation supports specific flags, which can be
 *                          passed in @a param by @ref ucp_request_param_t.flags.
 *                          The exact set of flags is defined by
 *                          @ref ucp_stream_recv_flags_t.
 *
 * @return NULL                 - The receive operation was completed
 *                                immediately. In this case the value pointed by
 *                                @a length is updated by the size of received
 *                                data. Note @a param->recv_info is not relevant
 *                                for this function.
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise            - Operation was scheduled for receive. A request
 *                                handle is returned to the application in order
 *                                to track progress of the operation.
 *
 * @note The amount of data received, in bytes, is always an integral multiple
 *       of the @a datatype size.
 */
ucs_status_ptr_t ucp_stream_recv_nbx(ucp_ep_h ep, void *buffer, size_t count,
                                     size_t *length,
                                     const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking stream receive operation of unstructured data into
 *        a UCP-supplied buffer.
 *
 * This routine receives any available data from endpoint @a ep.
 * Unlike @ref ucp_stream_recv_nb, the returned data is unstructured and is
 * treated as an array of bytes. If data is immediately available,
 * UCS_STATUS_PTR(_ptr) is returned as a pointer to the data, and @a length
 * is set to the size of the returned data buffer. The routine is non-blocking
 * and therefore returns immediately.
 *
 * @param [in]   ep               UCP endpoint that is used for the receive
 *                                operation.
 * @param [out]  length           Length of received data.
 *
 * @return NULL                 - No received data available on the @a ep.
 * @return UCS_PTR_IS_ERR(_ptr) - the receive operation failed and
 *                                UCS_PTR_STATUS(_ptr) indicates an error.
 * @return otherwise            - The pointer to the data UCS_STATUS_PTR(_ptr)
 *                                is returned to the application. After the data
 *                                is processed, the application is responsible
 *                                for releasing the data buffer by calling the
 *                                @ref ucp_stream_data_release routine.
 *
 * @note This function returns packed data (equivalent to ucp_dt_make_contig(1)).
 * @note This function returns a pointer to a UCP-supplied buffer, whereas
 *       @ref ucp_stream_recv_nb places the data into a user-provided buffer.
 *       In some cases, receiving data directly into a UCP-supplied buffer can
 *       be more optimal, for example by processing the incoming data in-place
 *       and thus avoiding extra memory copy operations.
 */
ucs_status_ptr_t ucp_stream_recv_data_nb(ucp_ep_h ep, size_t *length);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking tagged-receive operation.
 *
 * This routine receives a message that is described by the local address @a
 * buffer, size @a count, and @a datatype object on the @a worker. The tag
 * value of the receive message has to match the @a tag and @a tag_mask values,
 * where the @a tag_mask indicates which bits of the tag have to be matched. The
 * routine is non-blocking and therefore returns immediately. The receive
 * operation is considered completed when the message is delivered to the @a
 * buffer.  In order to notify the application about completion of the receive
 * operation the UCP library will invoke the call-back @a cb when the received
 * message is in the receive buffer and ready for application access.  If the
 * receive operation cannot be stated the routine returns an error.
 *
 * @note This routine cannot return UCS_OK. It always returns a request
 *       handle or an error.
 *
 * @param [in]  worker      UCP worker that is used for the receive operation.
 * @param [in]  buffer      Pointer to the buffer to receive the data to.
 * @param [in]  count       Number of elements to receive
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  tag         Message tag to expect.
 * @param [in]  tag_mask    Bit mask that indicates the bits that are used for
 *                          the matching of the incoming tag
 *                          against the expected tag.
 * @param [in]  cb          Callback function that is invoked whenever the
 *                          receive operation is completed and the data is ready
 *                          in the receive @a buffer.
 *
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise          - Operation was scheduled for receive. The request
 *                              handle is returned to the application in order
 *                              to track progress of the operation. The
 *                              application is responsible for releasing the
 *                              handle using @ref ucp_request_free
 *                              "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_tag_recv_nb(ucp_worker_h worker, void *buffer, size_t count,
                                 ucp_datatype_t datatype, ucp_tag_t tag,
                                 ucp_tag_t tag_mask, ucp_tag_recv_callback_t cb);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking tagged-receive operation.
 *
 * This routine receives a message that is described by the local address @a
 * buffer, size @a count, and @a datatype object on the @a worker. The tag
 * value of the receive message has to match the @a tag and @a tag_mask values,
 * where the @a tag_mask indicates which bits of the tag have to be matched. The
 * routine is non-blocking and therefore returns immediately. The receive
 * operation is considered completed when the message is delivered to the @a
 * buffer. In order to monitor completion of the operation
 * @ref ucp_request_check_status or @ref ucp_tag_recv_request_test should be
 * used.
 *
 * @param [in]  worker      UCP worker that is used for the receive operation.
 * @param [in]  buffer      Pointer to the buffer to receive the data to.
 * @param [in]  count       Number of elements to receive
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  tag         Message tag to expect.
 * @param [in]  tag_mask    Bit mask that indicates the bits that are used for
 *                          the matching of the incoming tag
 *                          against the expected tag.
 * @param [in]  req         Request handle allocated by the user. There should
 *                          be at least UCP request size bytes of available
 *                          space before the @a req. The size of UCP request
 *                          can be obtained by @ref ucp_context_query function.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_tag_recv_nbr(ucp_worker_h worker, void *buffer, size_t count,
                              ucp_datatype_t datatype, ucp_tag_t tag,
                              ucp_tag_t tag_mask, void *req);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking tagged-receive operation.
 *
 * This routine receives a message that is described by the local address @a
 * buffer, size @a count, and @a info object on the @a worker. The tag
 * value of the receive message has to match the @a tag and @a tag_mask values,
 * where the @a tag_mask indicates what bits of the tag have to be matched. The
 * routine is a non-blocking and therefore returns immediately. The receive
 * operation is considered completed when the message is delivered to the @a
 * buffer.  In order to notify the application about completion of the receive
 * operation the UCP library will invoke the call-back @a cb when the received
 * message is in the receive buffer and ready for application access.  If the
 * receive operation cannot be stated the routine returns an error.
 *
 * @param [in]  worker      UCP worker that is used for the receive operation.
 * @param [in]  buffer      Pointer to the buffer to receive the data to.
 * @param [in]  count       Number of elements to receive
 * @param [in]  tag         Message tag to expect.
 * @param [in]  tag_mask    Bit mask that indicates the bits that are used for
 *                          the matching of the incoming tag
 *                          against the expected tag.
 * @param [in]  param       Operation parameters, see @ref ucp_request_param_t
 *
 * @return NULL                 - The receive operation was completed
 *                                immediately. In this case, if
 *                                @a param->recv_info.tag_info is specified in the
 *                                @a param, the value to which it points is updated
 *                                with the information about the received message.
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise            - Operation was scheduled for receive. The request
 *                                handle is returned to the application in order
 *                                to track progress of the operation. The
 *                                application is responsible for releasing the
 *                                handle using @ref ucp_request_free
 *                                "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_tag_recv_nbx(ucp_worker_h worker, void *buffer, size_t count,
                                  ucp_tag_t tag, ucp_tag_t tag_mask,
                                  const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking probe and return a message.
 *
 * This routine probes (checks) if a messages described by the @a tag and
 * @a tag_mask was received (fully or partially) on the @a worker. The tag
 * value of the received message has to match the @a tag and @a tag_mask
 * values, where the @a tag_mask indicates what bits of the tag have to be
 * matched. The function returns immediately and if the message is matched it
 * returns a handle for the message.
 *
 * @param [in]  worker      UCP worker that is used for the probe operation.
 * @param [in]  tag         Message tag to probe for.
 * @param [in]  tag_mask    Bit mask that indicates the bits that are used for
 *                          the matching of the incoming tag
 *                          against the expected tag.
 * @param [in]  remove      The flag indicates if the matched message has to
 *                          be removed from UCP library.
 *                          If true (1), the message handle is removed from
 *                          the UCP library and the application is responsible
 *                          to call @ref ucp_tag_msg_recv_nb
 *                          "ucp_tag_msg_recv_nb()" in order to receive the data
 *                          and release the resources associated with the
 *                          message handle.
 *                          If false (0), the return value is merely an indication
 *                          to whether a matching message is present, and it cannot
 *                          be used in any other way, and in particular it cannot
 *                          be passed to @ref ucp_tag_msg_recv_nb().
 * @param [out] info        If the matching message is found the descriptor is
 *                          filled with the details about the message.
 *
 * @return NULL                      - No match found.
 * @return Message handle (not NULL) - If message is matched the message handle
 *                                     is returned.
 *
 * @note This function does not advance the communication state of the network.
 *       If this routine is used in busy-poll mode, need to make sure
 *       @ref ucp_worker_progress() is called periodically to extract messages
 *       from the transport.
 */
ucp_tag_message_h ucp_tag_probe_nb(ucp_worker_h worker, ucp_tag_t tag,
                                   ucp_tag_t tag_mask, int remove,
                                   ucp_tag_recv_info_t *info);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking receive operation for a probed message.
 *
 * This routine receives a message that is described by the local address @a
 * buffer, size @a count, @a message handle, and @a datatype object on the @a
 * worker. The @a message handle can be obtained by calling the @ref
 * ucp_tag_probe_nb "ucp_tag_probe_nb()" routine. The @ref ucp_tag_msg_recv_nb
 * "ucp_tag_msg_recv_nb()" routine is non-blocking and therefore returns
 * immediately. The receive operation is considered completed when the message
 * is delivered to the @a buffer. In order to notify the application about
 * completion of the receive operation the UCP library will invoke the
 * call-back @a cb when the received message is in the receive buffer and ready
 * for application access. If the receive operation cannot be started the
 * routine returns an error.
 *
 * @param [in]  worker      UCP worker that is used for the receive operation.
 * @param [in]  buffer      Pointer to the buffer that will receive the data.
 * @param [in]  count       Number of elements to receive
 * @param [in]  datatype    Datatype descriptor for the elements in the buffer.
 * @param [in]  message     Message handle.
 * @param [in]  cb          Callback function that is invoked whenever the
 *                          receive operation is completed and the data is ready
 *                          in the receive @a buffer.
 *
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise          - Operation was scheduled for receive. The request
 *                              handle is returned to the application in order
 *                              to track progress of the operation. The
 *                              application is responsible for releasing the
 *                              handle using @ref ucp_request_free
 *                              "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_tag_msg_recv_nb(ucp_worker_h worker, void *buffer,
                                     size_t count, ucp_datatype_t datatype,
                                     ucp_tag_message_h message,
                                     ucp_tag_recv_callback_t cb);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking receive operation for a probed message.
 *
 * This routine receives a message that is described by the local address @a
 * buffer, size @a count, and @a message handle on the @a worker.
 * The @a message handle can be obtained by calling the @ref
 * ucp_tag_probe_nb "ucp_tag_probe_nb()" routine. The @ref ucp_tag_msg_recv_nbx
 * "ucp_tag_msg_recv_nbx()" routine is non-blocking and therefore returns
 * immediately. The receive operation is considered completed when the message
 * is delivered to the @a buffer. In order to notify the application about
 * completion of the receive operation the UCP library will invoke the
 * call-back @a cb when the received message is in the receive buffer and ready
 * for application access. If the receive operation cannot be started the
 * routine returns an error.
 *
 * @param [in]  worker      UCP worker that is used for the receive operation.
 * @param [in]  buffer      Pointer to the buffer that will receive the data.
 * @param [in]  count       Number of elements to receive
 * @param [in]  message     Message handle.
 * @param [in]  param       Operation parameters, see @ref ucp_request_param_t
 *
 * @return UCS_PTR_IS_ERR(_ptr) - The receive operation failed.
 * @return otherwise            - Operation was scheduled for receive. The request
 *                                handle is returned to the application in order
 *                                to track progress of the operation. The
 *                                application is responsible for releasing the
 *                                handle using @ref ucp_request_free
 *                                "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_tag_msg_recv_nbx(ucp_worker_h worker, void *buffer,
                                      size_t count, ucp_tag_message_h message,
                                      const ucp_request_param_t *param);

/**
 * @ingroup UCP_COMM
 * @brief Non-blocking implicit remote memory put operation.
 *
 * This routine initiates a storage of contiguous block of data that is
 * described by the local address @a buffer in the remote contiguous memory
 * region described by @a remote_addr address and the @ref ucp_rkey_h "memory
 * handle" @a rkey. The routine returns immediately and @b does @b not
 * guarantee re-usability of the source address @e buffer. If the operation is
 * completed immediately the routine return UCS_OK, otherwise UCS_INPROGRESS
 * or an error is returned to user.
 *
 * @note A user can use @ref ucp_worker_flush_nb "ucp_worker_flush_nb()"
 * in order to guarantee re-usability of the source address @e buffer.
 *
 * @param [in]  ep           Remote endpoint handle.
 * @param [in]  buffer       Pointer to the local source address.
 * @param [in]  length       Length of the data (in bytes) stored under the
 *                           source address.
 * @param [in]  remote_addr  Pointer to the destination remote memory address
 *                           to write to.
 * @param [in]  rkey         Remote memory key associated with the
 *                           remote memory address.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_put_nbi(ucp_ep_h ep, const void *buffer, size_t length,
                         uint64_t remote_addr, ucp_rkey_h rkey);

/**
 * @ingroup UCP_COMM
 * @brief Non-blocking remote memory put operation.
 *
 * This routine initiates a storage of contiguous block of data that is
 * described by the local address @a buffer in the remote contiguous memory
 * region described by @a remote_addr address and the @ref ucp_rkey_h "memory
 * handle" @a rkey.  The routine returns immediately and @b does @b not
 * guarantee re-usability of the source address @e buffer. If the operation is
 * completed immediately the routine return UCS_OK, otherwise UCS_INPROGRESS
 * or an error is returned to user. If the put operation completes immediately,
 * the routine returns UCS_OK and the call-back routine @a cb is @b not
 * invoked. If the operation is @b not completed immediately and no error is
 * reported, then the UCP library will schedule invocation of the call-back
 * routine @a cb upon completion of the put operation. In other words, the
 * completion of a put operation can be signaled by the return code or
 * execution of the call-back.
 *
 * @note A user can use @ref ucp_worker_flush_nb "ucp_worker_flush_nb()"
 * in order to guarantee re-usability of the source address @e buffer.
 *
 * @param [in]  ep           Remote endpoint handle.
 * @param [in]  buffer       Pointer to the local source address.
 * @param [in]  length       Length of the data (in bytes) stored under the
 *                           source address.
 * @param [in]  remote_addr  Pointer to the destination remote memory address
 *                           to write to.
 * @param [in]  rkey         Remote memory key associated with the
 *                           remote memory address.
 * @param [in]  cb           Call-back function that is invoked whenever the
 *                           put operation is completed and the local buffer
 *                           can be modified. Does not guarantee remote
 *                           completion.
 *
 * @return NULL                 - The operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The operation failed.
 * @return otherwise            - Operation was scheduled and can be
 *                              completed at any point in time. The request handle
 *                              is returned to the application in order to track
 *                              progress of the operation. The application is
 *                              responsible for releasing the handle using
 *                              @ref ucp_request_free "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_put_nb(ucp_ep_h ep, const void *buffer, size_t length,
                            uint64_t remote_addr, ucp_rkey_h rkey,
                            ucp_send_callback_t cb);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking remote memory put operation.
 *
 * This routine initiates a storage of contiguous block of data that is
 * described by the local address @a buffer in the remote contiguous memory
 * region described by @a remote_addr address and the @ref ucp_rkey_h "memory
 * handle" @a rkey.  The routine returns immediately and @b does @b not
 * guarantee re-usability of the source address @e buffer. If the operation is
 * completed immediately the routine return UCS_OK, otherwise UCS_INPROGRESS
 * or an error is returned to user. If the put operation completes immediately,
 * the routine returns UCS_OK and the call-back routine @a param.cb.send is
 * @b not invoked. If the operation is @b not completed immediately and no
 * error is reported, then the UCP library will schedule invocation of the
 * call-back routine @a param.cb.send upon completion of the put operation.
 * In other words, the completion of a put operation can be signaled by the
 * return code or execution of the call-back.
 * Immediate completion signals can be fine-tuned via the
 * @ref ucp_request_param_t.op_attr_mask field in the
 * @ref ucp_request_param_t structure. The values of this field
 * are a bit-wise OR of the @ref ucp_op_attr_t enumeration.
 *
 * @note A user can use @ref ucp_worker_flush_nb "ucp_worker_flush_nb()"
 * in order to guarantee re-usability of the source address @e buffer.
 *
 * @param [in]  ep           Remote endpoint handle.
 * @param [in]  buffer       Pointer to the local source address.
 * @param [in]  count        Number of elements of type
 *                           @ref ucp_request_param_t.datatype to put. If
 *                           @ref ucp_request_param_t.datatype is not specified,
 *                           the type defaults to ucp_dt_make_contig(1), which
 *                           corresponds to byte elements.
 * @param [in]  remote_addr  Pointer to the destination remote memory address
 *                           to write to.
 * @param [in]  rkey         Remote memory key associated with the
 *                           remote memory address.
 * @param [in]  param       Operation parameters, see @ref ucp_request_param_t
 *
 * @return UCS_OK               - The operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The operation failed.
 * @return otherwise            - Operation was scheduled and can be
 *                                completed at any point in time. The request handle
 *                                is returned to the application in order to track
 *                                progress of the operation. The application is
 *                                responsible for releasing the handle using
 *                                @ref ucp_request_free "ucp_request_free()" routine.
 * 
 * @note Only the datatype ucp_dt_make_contig(1) is supported
 * for @a param->datatype, see @ref ucp_dt_make_contig.
 */
ucs_status_ptr_t ucp_put_nbx(ucp_ep_h ep, const void *buffer, size_t count,
                             uint64_t remote_addr, ucp_rkey_h rkey,
                             const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking implicit remote memory get operation.
 *
 * This routine initiate a load of contiguous block of data that is described
 * by the remote memory address @a remote_addr and the @ref ucp_rkey_h "memory handle"
 * @a rkey in the local contiguous memory region described by @a buffer
 * address. The routine returns immediately and @b does @b not guarantee that
 * remote data is loaded and stored under the local address @e buffer.
 *
 * @note A user can use @ref ucp_worker_flush_nb "ucp_worker_flush_nb()" in order
 * guarantee that remote data is loaded and stored under the local address
 * @e buffer.
 *
 * @param [in]  ep           Remote endpoint handle.
 * @param [in]  buffer       Pointer to the local destination address.
 * @param [in]  length       Length of the data (in bytes) stored under the
 *                           destination address.
 * @param [in]  remote_addr  Pointer to the source remote memory address
 *                           to read from.
 * @param [in]  rkey         Remote memory key associated with the
 *                           remote memory address.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_get_nbi(ucp_ep_h ep, void *buffer, size_t length,
                         uint64_t remote_addr, ucp_rkey_h rkey);

/**
 * @ingroup UCP_COMM
 * @brief Non-blocking remote memory get operation.
 *
 * This routine initiates a load of a contiguous block of data that is
 * described by the remote memory address @a remote_addr and the @ref ucp_rkey_h
 * "memory handle" @a rkey in the local contiguous memory region described
 * by @a buffer address. The routine returns immediately and @b does @b not
 * guarantee that remote data is loaded and stored under the local address @e
 * buffer. If the operation is completed immediately the routine return UCS_OK,
 * otherwise UCS_INPROGRESS or an error is returned to user. If the get
 * operation completes immediately, the routine returns UCS_OK and the
 * call-back routine @a cb is @b not invoked. If the operation is @b not
 * completed immediately and no error is reported, then the UCP library will
 * schedule invocation of the call-back routine @a cb upon completion of the
 * get operation. In other words, the completion of a get operation can be
 * signaled by the return code or execution of the call-back.
 *
 * @note A user can use @ref ucp_worker_flush_nb "ucp_worker_flush_nb()"
 * in order to guarantee re-usability of the source address @e buffer.
 *
 * @param [in]  ep           Remote endpoint handle.
 * @param [in]  buffer       Pointer to the local destination address.
 * @param [in]  length       Length of the data (in bytes) stored under the
 *                           destination address.
 * @param [in]  remote_addr  Pointer to the source remote memory address
 *                           to read from.
 * @param [in]  rkey         Remote memory key associated with the
 *                           remote memory address.
 * @param [in]  cb           Call-back function that is invoked whenever the
 *                           get operation is completed and the data is
 *                           visible to the local process.
 *
 * @return NULL                 - The operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The operation failed.
 * @return otherwise            - Operation was scheduled and can be
 *                              completed at any point in time. The request handle
 *                              is returned to the application in order to track
 *                              progress of the operation. The application is
 *                              responsible for releasing the handle using
 *                              @ref ucp_request_free "ucp_request_free()" routine.
 */
ucs_status_ptr_t ucp_get_nb(ucp_ep_h ep, void *buffer, size_t length,
                            uint64_t remote_addr, ucp_rkey_h rkey,
                            ucp_send_callback_t cb);


/**
 * @ingroup UCP_COMM
 * @brief Non-blocking remote memory get operation.
 *
 * This routine initiates a load of a contiguous block of data that is
 * described by the remote memory address @a remote_addr and the @ref ucp_rkey_h
 * "memory handle" @a rkey in the local contiguous memory region described
 * by @a buffer address. The routine returns immediately and @b does @b not
 * guarantee that remote data is loaded and stored under the local address @e
 * buffer. If the operation is completed immediately the routine return UCS_OK,
 * otherwise UCS_INPROGRESS or an error is returned to user. If the get
 * operation completes immediately, the routine returns UCS_OK and the
 * call-back routine @a param.cb.send is @b not invoked. If the operation is
 * @b not completed immediately and no error is reported, then the UCP library
 * will schedule invocation of the call-back routine @a param.cb.send upon
 * completion of the get operation. In other words, the completion of a get
 * operation can be signaled by the return code or execution of the call-back.
 *
 * @note A user can use @ref ucp_worker_flush_nb "ucp_worker_flush_nb()"
 * in order to guarantee re-usability of the source address @e buffer.
 *
 * @param [in]  ep           Remote endpoint handle.
 * @param [in]  buffer       Pointer to the local destination address.
 * @param [in]  count        Number of elements of type
 *                           @ref ucp_request_param_t.datatype to put. If
 *                           @ref ucp_request_param_t.datatype is not specified,
 *                           the type defaults to ucp_dt_make_contig(1), which
 *                           corresponds to byte elements.
 * @param [in]  remote_addr  Pointer to the source remote memory address
 *                           to read from.
 * @param [in]  rkey         Remote memory key associated with the
 *                           remote memory address.
 * @param [in]  param        Operation parameters, see @ref ucp_request_param_t.
 *
 * @return UCS_OK               - The operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The operation failed.
 * @return otherwise            - Operation was scheduled and can be
 *                                completed at any point in time. The request handle
 *                                is returned to the application in order to track
 *                                progress of the operation. The application is
 *                                responsible for releasing the handle using
 *                                @ref ucp_request_free "ucp_request_free()" routine.
 * 
 * @note Only the datatype ucp_dt_make_contig(1) is supported
 * for @a param->datatype, see @ref ucp_dt_make_contig.
 */
ucs_status_ptr_t ucp_get_nbx(ucp_ep_h ep, void *buffer, size_t count,
                             uint64_t remote_addr, ucp_rkey_h rkey,
                             const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Post an atomic memory operation.
 *
 * This routine posts an atomic memory operation to a remote value.
 * The remote value is described by the combination of the remote
 * memory address @a remote_addr and the @ref ucp_rkey_h "remote memory handle"
 * @a rkey.
 * Return from the function does not guarantee completion. A user must
 * call @ref ucp_ep_flush_nb or @ref ucp_worker_flush_nb to guarantee that the
 * remote value has been updated.
 *
 * @param [in] ep          UCP endpoint.
 * @param [in] opcode      One of @ref ucp_atomic_post_op_t.
 * @param [in] value       Source operand for the atomic operation.
 * @param [in] op_size     Size of value in bytes
 * @param [in] remote_addr Remote address to operate on.
 * @param [in] rkey        Remote key handle for the remote memory address.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_atomic_post(ucp_ep_h ep, ucp_atomic_post_op_t opcode, uint64_t value,
                             size_t op_size, uint64_t remote_addr, ucp_rkey_h rkey);


/**
 * @ingroup UCP_COMM
 * @brief Post an atomic fetch operation.
 *
 * This routine will post an atomic fetch operation to remote memory.
 * The remote value is described by the combination of the remote
 * memory address @a remote_addr and the @ref ucp_rkey_h "remote memory handle"
 * @a rkey.
 * The routine is non-blocking and therefore returns immediately. However the
 * actual atomic operation may be delayed. The atomic operation is not considered complete
 * until the values in remote and local memory are completed. If the atomic operation
 * completes immediately, the routine returns UCS_OK and the call-back routine
 * @a cb is @b not invoked. If the operation is @b not completed immediately and no
 * error is reported, then the UCP library will schedule invocation of the call-back
 * routine @a cb upon completion of the atomic operation. In other words, the completion
 * of an atomic operation can be signaled by the return code or execution of the call-back.
 *
 * @note The user should not modify any part of the @a result after this
 *       operation is called, until the operation completes.
 *
 * @param [in] ep          UCP endpoint.
 * @param [in] opcode      One of @ref ucp_atomic_fetch_op_t.
 * @param [in] value       Source operand for atomic operation. In the case of CSWAP
 *                         this is the conditional for the swap. For SWAP this is
 *                         the value to be placed in remote memory.
 * @param [inout] result   Local memory address to store resulting fetch to.
 *                         In the case of CSWAP the value in result will be
 *                         swapped into the @a remote_addr if the condition
 *                         is true.
 * @param [in] op_size     Size of value in bytes and pointer type for result
 * @param [in] remote_addr Remote address to operate on.
 * @param [in] rkey        Remote key handle for the remote memory address.
 * @param [in] cb          Call-back function that is invoked whenever the
 *                         send operation is completed. It is important to note
 *                         that the call-back function is only invoked in a case when
 *                         the operation cannot be completed in place.
 *
 * @return NULL                 - The operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The operation failed.
 * @return otherwise            - Operation was scheduled and can be
 *                              completed at any point in time. The request handle
 *                              is returned to the application in order to track
 *                              progress of the operation. The application is
 *                              responsible for releasing the handle using
 *                              @ref ucp_request_free "ucp_request_free()" routine.
 */
ucs_status_ptr_t
ucp_atomic_fetch_nb(ucp_ep_h ep, ucp_atomic_fetch_op_t opcode,
                    uint64_t value, void *result, size_t op_size,
                    uint64_t remote_addr, ucp_rkey_h rkey,
                    ucp_send_callback_t cb);


/**
 * @ingroup UCP_COMM
 * @brief Post an atomic memory operation.
 *
 * This routine will post an atomic operation to remote memory.
 * The remote value is described by the combination of the remote
 * memory address @a remote_addr and the @ref ucp_rkey_h "remote memory handle"
 * @a rkey. The routine is non-blocking and therefore returns immediately.
 * However, the actual atomic operation may be delayed. In order to enable
 * fetching semantics for atomic operations user has to specify
 * @a param.reply_buffer. Please see @ref atomic_ops "table" below for more
 * details.
 *
 * @note    The user should not modify any part of the @a buffer (or also
 *          @a param->reply_buffer for fetch operations), until the operation
 *          completes.
 * @note    Only ucp_dt_make_config(4) and ucp_dt_make_contig(8) are supported
 *          in @a param->datatype, see @ref ucp_dt_make_contig. Also, currently
 *          atomic operations can handle one element only. Thus, @a count
 *          argument must be set to 1.
 *
 * <table>
 * <caption id="atomic_ops">Atomic Operations Semantic</caption>
 * <tr> <th align="center">Atomic Operation <th align="center">Pseudo code
 *      <th align="center">X <th align="center">Y <th align="center">Z
 *      <th align="center">Result
 * <tr> <td align="left">@ref UCP_ATOMIC_OP_ADD <td align="left"> Result=Y; Y+=X
 *      <td align="left">buffer<td align="left">remote_addr<td align="center">-
 *      <td align="left">param.reply_buffer(optional)
 * <tr> <td align="left">@ref UCP_ATOMIC_OP_SWAP <td align="left"> Result=Y; Y=X
 *      <td align="left">buffer<td align="left">remote_addr <td align="center">-
 *      <td align="left">param.reply_buffer
 * <tr> <td align="left">@ref UCP_ATOMIC_OP_CSWAP
 *      <td align="left">Result=Y; if (X==Y) then Y=Z<td align="left">buffer
 *      <td align="left">remote_addr <td align="left">param.reply_buffer
 *      <td align="left">param.reply_buffer
 * <tr> <td align="left">@ref UCP_ATOMIC_OP_AND <td align="left"> Result=Y; Y&=X
 *      <td align="left">buffer<td align="left">remote_addr <td align="center">-
 *      <td align="left">param.reply_buffer(optional)
 * <tr> <td align="left">@ref UCP_ATOMIC_OP_OR <td align="left"> Result=Y; Y|=X
 *      <td align="left">buffer<td align="left">remote_addr <td align="center">-
 *      <td align="left">param.reply_buffer(optional)
 * <tr> <td align="left">@ref UCP_ATOMIC_OP_XOR <td align="left"> Result=Y; Y^=X
 *      <td align="left">buffer<td align="left">remote_addr <td align="center">-
 *      <td align="left">param.reply_buffer(optional)
 * </table>
 *
 * @param [in] ep          UCP endpoint.
 * @param [in] opcode      One of @ref ucp_atomic_op_t.
 * @param [in] buffer      Address of operand for the atomic operation. See
 *                         @ref atomic_ops "Atomic Operations Semantic table"
 *                         for exact usage by different atomic operations.
 * @param [in] count       Number of elements in @a buffer and @a result. The
 *                         size of each element is specified by
 *                         @ref ucp_request_param_t.datatype
 * @param [in] remote_addr Remote address to operate on.
 * @param [in] rkey        Remote key handle for the remote memory address.
 * @param [in] param       Operation parameters, see @ref ucp_request_param_t.
 *
 * @return NULL                 - The operation completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The operation failed.
 * @return otherwise            - Operation was scheduled and can be
 *                                completed at some time in the future. The
 *                                request handle is returned to the application
 *                                in order to track progress of the operation.
 */
ucs_status_ptr_t
ucp_atomic_op_nbx(ucp_ep_h ep, ucp_atomic_op_t opcode, const void *buffer,
                  size_t count, uint64_t remote_addr, ucp_rkey_h rkey,
                  const ucp_request_param_t *param);


/**
 * @ingroup UCP_COMM
 * @brief Check the status of non-blocking request.
 *
 * This routine checks the state of the request and returns its current status.
 * Any value different from UCS_INPROGRESS means that request is in a completed
 * state.
 *
 * @param [in]  request     Non-blocking request to check.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_request_check_status(void *request);


/**
 * @ingroup UCP_COMM
 * @brief Check the status and currently available state of non-blocking request
 *        returned from @ref ucp_tag_recv_nb routine.
 *
 * This routine checks the state and returns current status of the request
 * returned from @ref ucp_tag_recv_nb routine or the user allocated request
 * for @ref ucp_tag_recv_nbr. Any value different from UCS_INPROGRESS means
 * that the request is in a completed state.
 *
 * @param [in]  request     Non-blocking request to check.
 * @param [out] info        It is filled with the details about the message
 *                          available at the moment of calling.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_tag_recv_request_test(void *request, ucp_tag_recv_info_t *info);


/**
 * @ingroup UCP_COMM
 * @brief Check the status and currently available state of non-blocking request
 *        returned from @ref ucp_stream_recv_nb routine.
 *
 * This routine checks the state and returns current status of the request
 * returned from @ref ucp_stream_recv_nb routine. Any value different from
 * UCS_INPROGRESS means that the request is in a completed state.
 *
 * @param [in]  request     Non-blocking request to check.
 * @param [out] length_p    The size of the received data in bytes. This value
 *                          is only valid if the status is UCS_OK. If valid, it
 *                          is always an integral multiple of the datatype size
 *                          associated with the request.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_stream_recv_request_test(void *request, size_t *length_p);

/**
 * @ingroup UCP_COMM
 * @brief Cancel an outstanding communications request.
 *
 * @param [in]  worker       UCP worker.
 * @param [in]  request      Non-blocking request to cancel.
 *
 * This routine tries to cancels an outstanding communication request.  After
 * calling this routine, the @a request will be in completed or canceled (but
 * not both) state regardless of the status of the target endpoint associated
 * with the communication request.  If the request is completed successfully,
 * the @ref ucp_send_callback_t "send" or @ref ucp_tag_recv_callback_t
 * "receive" completion callbacks (based on the type of the request) will be
 * called with the @a status argument of the callback set to UCS_OK, and in a
 * case it is canceled the @a status argument is set to UCS_ERR_CANCELED.  It is
 * important to note that in order to release the request back to the library
 * the application is responsible for calling @ref ucp_request_free
 * "ucp_request_free()".
 */
void ucp_request_cancel(ucp_worker_h worker, void *request);


/**
 * @ingroup UCP_COMM
 * @brief Release UCP data buffer returned by @ref ucp_stream_recv_data_nb.
 *
 * @param [in]  ep        Endpoint @a data received from.
 * @param [in]  data      Data pointer to release, which was returned from
 *                        @ref ucp_stream_recv_data_nb.
 *
 * This routine releases internal UCP data buffer returned by
 * @ref ucp_stream_recv_data_nb when @a data is processed, the application can't
 * use this buffer after calling this function.
 */
void ucp_stream_data_release(ucp_ep_h ep, void *data);


/**
 * @ingroup UCP_COMM
 * @brief Release a communications request.
 *
 * @param [in]  request      Non-blocking request to release.
 *
 * This routine releases the non-blocking request back to the library, regardless
 * of its current state. Communications operations associated with this request
 * will make progress internally, however no further notifications or callbacks
 * will be invoked for this request.
 */
void ucp_request_free(void *request);


/**
 * @ingroup UCP_COMM
 * @brief Create an empty communications request.
 *
 * @param [in]  worker       UCP worker.
 *
 * @return Error code as defined by @ref ucs_status_t
 *
 * This routine creates request which may be used in functions
 * @ref ucp_tag_send_nbx, @ref ucp_tag_recv_nbx, etc. The application
 * is responsible for releasing the handle using the @ref ucp_request_free
 * routine
 */
void *ucp_request_alloc(ucp_worker_h worker);


/**
 * @ingroup UCP_DATATYPE
 * @brief Create a generic datatype.
 *
 * This routine create a generic datatype object.
 * The generic datatype is described by the @a ops @ref ucp_generic_dt_ops_t
 * "object" which provides a table of routines defining the operations for
 * generic datatype manipulation. Typically, generic datatypes are used for
 * integration with datatype engines provided with MPI implementations (MPICH,
 * Open MPI, etc).
 * The application is responsible for releasing the @a datatype_p  object using
 * @ref ucp_dt_destroy "ucp_dt_destroy()" routine.
 *
 * @param [in]  ops          Generic datatype function table as defined by
 *                           @ref ucp_generic_dt_ops_t .
 * @param [in]  context      Application defined context passed to this
 *                           routine.  The context is passed as a parameter
 *                           to the routines in the @a ops table.
 * @param [out] datatype_p   A pointer to datatype object.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_dt_create_generic(const ucp_generic_dt_ops_t *ops, void *context,
                                   ucp_datatype_t *datatype_p);


/**
 * @ingroup UCP_DATATYPE
 * @brief Destroy a datatype and release its resources.
 *
 * This routine destroys the @a datatype object and
 * releases any resources that are associated with the object.
 * The @a datatype object must be allocated using @ref ucp_dt_create_generic
 * "ucp_dt_create_generic()" routine.
 *
 * @warning
 * @li Once the @a datatype object is released an access to this object may
 * cause an undefined failure.
 *
 * @param [in]  datatype     Datatype object to destroy.
 */
void ucp_dt_destroy(ucp_datatype_t datatype);


/**
 * @ingroup UCP_WORKER
 *
 * @brief Assures ordering between non-blocking operations
 *
 * This routine ensures ordering of non-blocking communication operations on
 * the @ref ucp_worker_h "UCP worker".  Communication operations issued on the
 * @a worker prior to this call are guaranteed to be completed before any
 * subsequent communication operations to the same @ref ucp_worker_h "worker"
 * which follow the call to @ref ucp_worker_fence "fence".
 *
 * @note The primary difference between @ref ucp_worker_fence "ucp_worker_fence()"
 * and the @ref ucp_worker_flush_nb "ucp_worker_flush_nb()" is the fact the fence
 * routine does not guarantee completion of the operations on the call return but
 * only ensures the order between communication operations. The
 * @ref ucp_worker_flush_nb "flush" operation on return guarantees that all
 * operations are completed and corresponding memory regions were updated.
 *
 * @param [in] worker        UCP worker.
 *
 * @return Error code as defined by @ref ucs_status_t
 */
ucs_status_t ucp_worker_fence(ucp_worker_h worker);


/**
 * @ingroup UCP_WORKER
 *
 * @brief Flush outstanding AMO and RMA operations on the @ref ucp_worker_h
 * "worker"
 *
 * This routine flushes all outstanding AMO and RMA communications on the
 * @ref ucp_worker_h "worker". All the AMO and RMA operations issued on the
 * @a worker prior to this call are completed both at the origin and at the
 * target when this call returns.
 *
 * @note For description of the differences between @ref ucp_worker_flush_nb
 * "flush" and @ref ucp_worker_fence "fence" operations please see
 * @ref ucp_worker_fence "ucp_worker_fence()"
 *
 * @param [in] worker    UCP worker.
 * @param [in] flags     Flags for flush operation. Reserved for future use.
 * @param [in] cb        Callback which will be called when the flush operation
 *                       completes.
 *
 * @return NULL             - The flush operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The flush operation failed.
 * @return otherwise        - Flush operation was scheduled and can be completed
 *                          in any point in time. The request handle is returned
 *                          to the application in order to track progress. The
 *                          application is responsible for releasing the handle
 *                          using @ref ucp_request_free "ucp_request_free()"
 *                          routine.
 */
ucs_status_ptr_t ucp_worker_flush_nb(ucp_worker_h worker, unsigned flags,
                                     ucp_send_callback_t cb);


/**
 * @ingroup UCP_WORKER
 *
 * @brief Flush outstanding AMO and RMA operations on the @ref ucp_worker_h
 * "worker"
 *
 * This routine flushes all outstanding AMO and RMA communications on the
 * @ref ucp_worker_h "worker". All the AMO and RMA operations issued on the
 * @a worker prior to this call are completed both at the origin and at the
 * target when this call returns.
 *
 * @note For description of the differences between @ref ucp_worker_flush_nb
 * "flush" and @ref ucp_worker_fence "fence" operations please see
 * @ref ucp_worker_fence "ucp_worker_fence()"
 *
 * @param [in] worker    UCP worker.
 * @param [in] param     Operation parameters, see @ref ucp_request_param_t
 *
 * @return NULL                 - The flush operation was completed immediately.
 * @return UCS_PTR_IS_ERR(_ptr) - The flush operation failed.
 * @return otherwise            - Flush operation was scheduled and can be
 *                                completed in any point in time. The request
 *                                handle is returned to the application in order
 *                                to track progress.
 */
ucs_status_ptr_t ucp_worker_flush_nbx(ucp_worker_h worker,
                                      const ucp_request_param_t *param);


/**
 * @example ucp_hello_world.c
 * UCP hello world client / server example utility.
 *
 * @example ucp_client_server.c
 * UCP client / server example using different APIs (tag, stream, am) utility.
 */

END_C_DECLS

#endif
