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//  Copyright (c) 1995-2020 Mort Bay Consulting Pty Ltd and others.
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//  All rights reserved. This program and the accompanying materials
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//  and Apache License v2.0 which accompanies this distribution.
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//      The Eclipse Public License is available at
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//      The Apache License v2.0 is available at
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package org.eclipse.jetty.util.thread;

/**
 * <p>An {@link ExecutionStrategy} executes {@link Runnable} tasks produced by a {@link Producer}.
 * The strategy to execute the task may vary depending on the implementation; the task may be
 * run in the calling thread, or in a new thread, etc.</p>
 * <p>The strategy delegates the production of tasks to a {@link Producer}, and continues to
 * execute tasks until the producer continues to produce them.</p>
 */
public interface ExecutionStrategy
{
    /**
     * <p>Initiates (or resumes) the task production and consumption.</p>
     * <p>This method guarantees that the task is never run by the
     * thread that called this method.</p>
     *
     * TODO review the need for this (only used by HTTP2 push)
     *
     * @see #produce()
     */
    void dispatch();

    /**
     * <p>Initiates (or resumes) the task production and consumption.</p>
     * <p>The produced task may be run by the same thread that called
     * this method.</p>
     *
     * @see #dispatch()
     */
    void produce();

    /**
     * <p>A producer of {@link Runnable} tasks to run.</p>
     * <p>The {@link ExecutionStrategy} will repeatedly invoke {@link #produce()} until
     * the producer returns null, indicating that it has nothing more to produce.</p>
     * <p>When no more tasks can be produced, implementations should arrange for the
     * {@link ExecutionStrategy} to be invoked again in case an external event resumes
     * the tasks production.</p>
     */
    interface Producer
    {
        /**
         * <p>Produces a task to be executed.</p>
         *
         * @return a task to executed or null if there are no more tasks to execute
         */
        Runnable produce();
    }
}
