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/* * @(#)Executor.java 1.9 06/01/30 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.concurrent; /** * An object that executes submitted {@link Runnable} tasks. This * interface provides a way of decoupling task submission from the * mechanics of how each task will be run, including details of thread * use, scheduling, etc. An <tt>Executor</tt> is normally used * instead of explicitly creating threads. For example, rather than * invoking <tt>new Thread(new(RunnableTask())).start()</tt> for each * of a set of tasks, you might use: * * <pre> * Executor executor = <em>anExecutor</em>; * executor.execute(new RunnableTask1()); * executor.execute(new RunnableTask2()); * ... * </pre> * * However, the <tt>Executor</tt> interface does not strictly * require that execution be asynchronous. In the simplest case, an * executor can run the submitted task immediately in the caller's * thread: * * <pre> * class DirectExecutor implements Executor { * public void execute(Runnable r) { * r.run(); * } * }</pre> * * More typically, tasks are executed in some thread other * than the caller's thread. The executor below spawns a new thread * for each task. * * <pre> * class ThreadPerTaskExecutor implements Executor { * public void execute(Runnable r) { * new Thread(r).start(); * } * }</pre> * * Many <tt>Executor</tt> implementations impose some sort of * limitation on how and when tasks are scheduled. The executor below * serializes the submission of tasks to a second executor, * illustrating a composite executor. * * <pre> * class SerialExecutor implements Executor { * final Queue<Runnable> tasks = new ArrayDeque<Runnable>(); * final Executor executor; * Runnable active; * * SerialExecutor(Executor executor) { * this.executor = executor; * } * * public synchronized void execute(final Runnable r) { * tasks.offer(new Runnable() { * public void run() { * try { * r.run(); * } finally { * scheduleNext(); * } * } * }); * if (active == null) { * scheduleNext(); * } * } * * protected synchronized void scheduleNext() { * if ((active = tasks.poll()) != null) { * executor.execute(active); * } * } * }</pre> * * The <tt>Executor</tt> implementations provided in this package * implement {@link ExecutorService}, which is a more extensive * interface. The {@link ThreadPoolExecutor} class provides an * extensible thread pool implementation. The {@link Executors} class * provides convenient factory methods for these Executors. * * <p>Memory consistency effects: Actions in a thread prior to * submitting a {@code Runnable} object to an {@code Executor} * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> * its execution begins, perhaps in another thread. * * @since 1.5 * @author Doug Lea */ public interface Executor { /** * Executes the given command at some time in the future. The command * may execute in a new thread, in a pooled thread, or in the calling * thread, at the discretion of the <tt>Executor</tt> implementation. * * @param command the runnable task * @throws RejectedExecutionException if this task cannot be * accepted for execution. * @throws NullPointerException if command is null */ void execute(Runnable command); }