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# acx_pthread

## Synopsis

`ACX_PTHREAD([ACTION-IF-FOUND[, ACTION-IF-NOT-FOUND]])`

## Description

This macro figures out how to build C programs using POSIX threads. It sets the PTHREAD_LIBS output variable to the threads library and linker flags, and the PTHREAD_CFLAGS output variable to any special C compiler flags that are needed. (The user can also force certain compiler flags/libs to be tested by setting these environment variables.)

Also sets PTHREAD_CC to any special C compiler that is needed for multi-threaded programs (defaults to the value of CC otherwise). (This is necessary on AIX to use the special cc_r compiler alias.)

NOTE: You are assumed to not only compile your program with these flags, but also link it with them as well. e.g. you should link with $PTHREAD_CC $CFLAGS $PTHREAD_CFLAGS $LDFLAGS ... $PTHREAD_LIBS $LIBS

If you are only building threads programs, you may wish to use these variables in your default LIBS, CFLAGS, and CC:

           LIBS="$PTHREAD_LIBS $LIBS"
           CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
           CC="$PTHREAD_CC"

In addition, if the PTHREAD_CREATE_JOINABLE thread-attribute constant has a nonstandard name, defines PTHREAD_CREATE_JOINABLE to that name (e.g. PTHREAD_CREATE_UNDETACHED on AIX).

ACTION-IF-FOUND is a list of shell commands to run if a threads library is found, and ACTION-IF-NOT-FOUND is a list of commands to run it if it is not found. If ACTION-IF-FOUND is not specified, the default action will define HAVE_PTHREAD.

Please let the authors know if this macro fails on any platform, or if you have any other suggestions or comments. This macro was based on work by SGJ on autoconf scripts for FFTW (http://www.fftw.org/) (with help from M. Frigo), as well as ac_pthread and hb_pthread macros posted by Alejandro Forero Cuervo to the autoconf macro repository. We are also grateful for the helpful feedback of numerous users.

## Author

Steven G. Johnson <stevenj@alum.mit.edu>

## Last Modified

2008-04-12

## Cross References

## M4 Source Code

    AC_DEFUN([ACX_PTHREAD], [
    AC_REQUIRE([AC_CANONICAL_HOST])
    AC_LANG_SAVE
    AC_LANG_C
    acx_pthread_ok=no

    # We used to check for pthread.h first, but this fails if pthread.h
    # requires special compiler flags (e.g. on True64 or Sequent).
    # It gets checked for in the link test anyway.

    # First of all, check if the user has set any of the PTHREAD_LIBS,
    # etcetera environment variables, and if threads linking works using
    # them:
    if test x"$PTHREAD_LIBS$PTHREAD_CFLAGS" != x; then
            save_CFLAGS="$CFLAGS"
            CFLAGS="$CFLAGS $PTHREAD_CFLAGS"
            save_LIBS="$LIBS"
            LIBS="$PTHREAD_LIBS $LIBS"
            AC_MSG_CHECKING([for pthread_join in LIBS=$PTHREAD_LIBS with CFLAGS=$PTHREAD_CFLAGS])
            AC_TRY_LINK_FUNC(pthread_join, acx_pthread_ok=yes)
            AC_MSG_RESULT($acx_pthread_ok)
            if test x"$acx_pthread_ok" = xno; then
                    PTHREAD_LIBS=""
                    PTHREAD_CFLAGS=""
            fi
            LIBS="$save_LIBS"
            CFLAGS="$save_CFLAGS"
    fi

    # We must check for the threads library under a number of different
    # names; the ordering is very important because some systems
    # (e.g. DEC) have both -lpthread and -lpthreads, where one of the
    # libraries is broken (non-POSIX).

    # Create a list of thread flags to try.  Items starting with a "-" are
    # C compiler flags, and other items are library names, except for "none"
    # which indicates that we try without any flags at all, and "pthread-config"
    # which is a program returning the flags for the Pth emulation library.

    acx_pthread_flags="pthreads none -Kthread -kthread lthread -pthread -pthreads -mthreads pthread --thread-safe -mt pthread-config"

    # The ordering *is* (sometimes) important.  Some notes on the
    # individual items follow:

    # pthreads: AIX (must check this before -lpthread)
    # none: in case threads are in libc; should be tried before -Kthread and
    #       other compiler flags to prevent continual compiler warnings
    # -Kthread: Sequent (threads in libc, but -Kthread needed for pthread.h)
    # -kthread: FreeBSD kernel threads (preferred to -pthread since SMP-able)
    # lthread: LinuxThreads port on FreeBSD (also preferred to -pthread)
    # -pthread: Linux/gcc (kernel threads), BSD/gcc (userland threads)
    # -pthreads: Solaris/gcc
    # -mthreads: Mingw32/gcc, Lynx/gcc
    # -mt: Sun Workshop C (may only link SunOS threads [-lthread], but it
    #      doesn't hurt to check since this sometimes defines pthreads too;
    #      also defines -D_REENTRANT)
    #      ... -mt is also the pthreads flag for HP/aCC
    # pthread: Linux, etcetera
    # --thread-safe: KAI C++
    # pthread-config: use pthread-config program (for GNU Pth library)

    case "${host_cpu}-${host_os}" in
            *solaris*)

            # On Solaris (at least, for some versions), libc contains stubbed
            # (non-functional) versions of the pthreads routines, so link-based
            # tests will erroneously succeed.  (We need to link with -pthreads/-mt/
            # -lpthread.)  (The stubs are missing pthread_cleanup_push, or rather
            # a function called by this macro, so we could check for that, but
            # who knows whether they'll stub that too in a future libc.)  So,
            # we'll just look for -pthreads and -lpthread first:

            acx_pthread_flags="-pthreads pthread -mt -pthread $acx_pthread_flags"
            ;;
    esac

    if test x"$acx_pthread_ok" = xno; then
    for flag in $acx_pthread_flags; do

            case $flag in
                    none)
                    AC_MSG_CHECKING([whether pthreads work without any flags])
                    ;;

                    -*)
                    AC_MSG_CHECKING([whether pthreads work with $flag])
                    PTHREAD_CFLAGS="$flag"
                    ;;

                    pthread-config)
                    AC_CHECK_PROG(acx_pthread_config, pthread-config, yes, no)
                    if test x"$acx_pthread_config" = xno; then continue; fi
                    PTHREAD_CFLAGS="`pthread-config --cflags`"
                    PTHREAD_LIBS="`pthread-config --ldflags` `pthread-config --libs`"
                    ;;

                    *)
                    AC_MSG_CHECKING([for the pthreads library -l$flag])
                    PTHREAD_LIBS="-l$flag"
                    ;;
            esac

            save_LIBS="$LIBS"
            save_CFLAGS="$CFLAGS"
            LIBS="$PTHREAD_LIBS $LIBS"
            CFLAGS="$CFLAGS $PTHREAD_CFLAGS"

            # Check for various functions.  We must include pthread.h,
            # since some functions may be macros.  (On the Sequent, we
            # need a special flag -Kthread to make this header compile.)
            # We check for pthread_join because it is in -lpthread on IRIX
            # while pthread_create is in libc.  We check for pthread_attr_init
            # due to DEC craziness with -lpthreads.  We check for
            # pthread_cleanup_push because it is one of the few pthread
            # functions on Solaris that doesn't have a non-functional libc stub.
            # We try pthread_create on general principles.
            AC_TRY_LINK([#include <pthread.h>],
                        [pthread_t th; pthread_join(th, 0);
                         pthread_attr_init(0); pthread_cleanup_push(0, 0);
                         pthread_create(0,0,0,0); pthread_cleanup_pop(0); ],
                        [acx_pthread_ok=yes])

            LIBS="$save_LIBS"
            CFLAGS="$save_CFLAGS"

            AC_MSG_RESULT($acx_pthread_ok)
            if test "x$acx_pthread_ok" = xyes; then
                    break;
            fi

            PTHREAD_LIBS=""
            PTHREAD_CFLAGS=""
    done
    fi

    # Various other checks:
    if test "x$acx_pthread_ok" = xyes; then
            save_LIBS="$LIBS"
            LIBS="$PTHREAD_LIBS $LIBS"
            save_CFLAGS="$CFLAGS"
            CFLAGS="$CFLAGS $PTHREAD_CFLAGS"

            # Detect AIX lossage: JOINABLE attribute is called UNDETACHED.
            AC_MSG_CHECKING([for joinable pthread attribute])
            attr_name=unknown
            for attr in PTHREAD_CREATE_JOINABLE PTHREAD_CREATE_UNDETACHED; do
                AC_TRY_LINK([#include <pthread.h>], [int attr=$attr; return attr;],
                            [attr_name=$attr; break])
            done
            AC_MSG_RESULT($attr_name)
            if test "$attr_name" != PTHREAD_CREATE_JOINABLE; then
                AC_DEFINE_UNQUOTED(PTHREAD_CREATE_JOINABLE, $attr_name,
                                   [Define to necessary symbol if this constant
                                    uses a non-standard name on your system.])
            fi

            AC_MSG_CHECKING([if more special flags are required for pthreads])
            flag=no
            case "${host_cpu}-${host_os}" in
                *-aix* | *-freebsd* | *-darwin*) flag="-D_THREAD_SAFE";;
                *solaris* | *-osf* | *-hpux*) flag="-D_REENTRANT";;
            esac
            AC_MSG_RESULT(${flag})
            if test "x$flag" != xno; then
                PTHREAD_CFLAGS="$flag $PTHREAD_CFLAGS"
            fi

            LIBS="$save_LIBS"
            CFLAGS="$save_CFLAGS"

            # More AIX lossage: must compile with xlc_r or cc_r
            if test x"$GCC" != xyes; then
              AC_CHECK_PROGS(PTHREAD_CC, xlc_r cc_r, ${CC})
            else
              PTHREAD_CC=$CC
            fi
    else
            PTHREAD_CC="$CC"
    fi

    AC_SUBST(PTHREAD_LIBS)
    AC_SUBST(PTHREAD_CFLAGS)
    AC_SUBST(PTHREAD_CC)

    # Finally, execute ACTION-IF-FOUND/ACTION-IF-NOT-FOUND:
    if test x"$acx_pthread_ok" = xyes; then
            ifelse([$1],,AC_DEFINE(HAVE_PTHREAD,1,[Define if you have POSIX threads libraries and header files.]),[$1])
            :
    else
            acx_pthread_ok=no
            $2
    fi
    AC_LANG_RESTORE
    ])dnl ACX_PTHREAD

## License

Copyright © 2008 Steven G. Johnson <stevenj@alum.mit.edu>

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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