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Utility classes for Jetty

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//
// ========================================================================
// Copyright (c) 1995-2021 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//

package org.eclipse.jetty.util.thread;

/**
 * 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.
 * The strategy delegates the production of tasks to a {@link Producer}, and continues to
 * execute tasks until the producer continues to produce them.
 */
public interface ExecutionStrategy
{
    /**
     * Initiates (or resumes) the task production and consumption.
     * This method guarantees that the task is never run by the
     * thread that called this method.
     *
     * TODO review the need for this (only used by HTTP2 push)
     *
     * @see #produce()
     */
    public void dispatch();

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

    /**
     * A producer of {@link Runnable} tasks to run.
     * The {@link ExecutionStrategy} will repeatedly invoke {@link #produce()} until
     * the producer returns null, indicating that it has nothing more to produce.
     * 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.
     */
    public interface Producer
    {
        /**
         * Produces a task to be executed.
         *
         * @return a task to executed or null if there are no more tasks to execute
         */
        Runnable produce();
    }
}