138 lines
4.8 KiB
Java
138 lines
4.8 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent;
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/**
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* An object that executes submitted {@link Runnable} tasks. This
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* interface provides a way of decoupling task submission from the
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* mechanics of how each task will be run, including details of thread
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* use, scheduling, etc. An {@code Executor} is normally used
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* instead of explicitly creating threads. For example, rather than
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* invoking {@code new Thread(new RunnableTask()).start()} for each
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* of a set of tasks, you might use:
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*
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* <pre> {@code
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* Executor executor = anExecutor();
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* executor.execute(new RunnableTask1());
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* executor.execute(new RunnableTask2());
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* ...}</pre>
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*
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* However, the {@code Executor} interface does not strictly require
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* that execution be asynchronous. In the simplest case, an executor
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* can run the submitted task immediately in the caller's thread:
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*
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* <pre> {@code
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* class DirectExecutor implements Executor {
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* public void execute(Runnable r) {
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* r.run();
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* }
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* }}</pre>
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*
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* More typically, tasks are executed in some thread other than the
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* caller's thread. The executor below spawns a new thread for each
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* task.
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*
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* <pre> {@code
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* class ThreadPerTaskExecutor implements Executor {
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* public void execute(Runnable r) {
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* new Thread(r).start();
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* }
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* }}</pre>
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*
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* Many {@code Executor} implementations impose some sort of
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* limitation on how and when tasks are scheduled. The executor below
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* serializes the submission of tasks to a second executor,
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* illustrating a composite executor.
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*
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* <pre> {@code
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* class SerialExecutor implements Executor {
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* final Queue<Runnable> tasks = new ArrayDeque<>();
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* final Executor executor;
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* Runnable active;
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*
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* SerialExecutor(Executor executor) {
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* this.executor = executor;
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* }
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*
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* public synchronized void execute(Runnable r) {
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* tasks.add(() -> {
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* try {
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* r.run();
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* } finally {
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* scheduleNext();
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* }
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* });
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* if (active == null) {
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* scheduleNext();
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* }
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* }
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*
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* protected synchronized void scheduleNext() {
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* if ((active = tasks.poll()) != null) {
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* executor.execute(active);
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* }
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* }
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* }}</pre>
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*
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* The {@code Executor} implementations provided in this package
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* implement {@link ExecutorService}, which is a more extensive
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* interface. The {@link ThreadPoolExecutor} class provides an
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* extensible thread pool implementation. The {@link Executors} class
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* provides convenient factory methods for these Executors.
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*
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* <p>Memory consistency effects: Actions in a thread prior to
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* submitting a {@code Runnable} object to an {@code Executor}
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* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
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* its execution begins, perhaps in another thread.
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*
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* @since 1.5
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* @author Doug Lea
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*/
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public interface Executor {
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/**
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* Executes the given command at some time in the future. The command
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* may execute in a new thread, in a pooled thread, or in the calling
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* thread, at the discretion of the {@code Executor} implementation.
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*
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* @param command the runnable task
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* @throws RejectedExecutionException if this task cannot be
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* accepted for execution
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* @throws NullPointerException if command is null
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*/
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void execute(Runnable command);
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}
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