ExecutorService.java revision 29957558cf0db700bfaae360a80c42dc3871d0e5 
1/*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.  Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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24
25/*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36package java.util.concurrent;
37
38import java.util.Collection;
39import java.util.List;
40
41// BEGIN android-note
42// removed security manager docs
43// END android-note
44
45/**
46 * An {@link Executor} that provides methods to manage termination and
47 * methods that can produce a {@link Future} for tracking progress of
48 * one or more asynchronous tasks.
49 *
50 * <p>An {@code ExecutorService} can be shut down, which will cause
51 * it to reject new tasks.  Two different methods are provided for
52 * shutting down an {@code ExecutorService}. The {@link #shutdown}
53 * method will allow previously submitted tasks to execute before
54 * terminating, while the {@link #shutdownNow} method prevents waiting
55 * tasks from starting and attempts to stop currently executing tasks.
56 * Upon termination, an executor has no tasks actively executing, no
57 * tasks awaiting execution, and no new tasks can be submitted.  An
58 * unused {@code ExecutorService} should be shut down to allow
59 * reclamation of its resources.
60 *
61 * <p>Method {@code submit} extends base method {@link
62 * Executor#execute(Runnable)} by creating and returning a {@link Future}
63 * that can be used to cancel execution and/or wait for completion.
64 * Methods {@code invokeAny} and {@code invokeAll} perform the most
65 * commonly useful forms of bulk execution, executing a collection of
66 * tasks and then waiting for at least one, or all, to
67 * complete. (Class {@link ExecutorCompletionService} can be used to
68 * write customized variants of these methods.)
69 *
70 * <p>The {@link Executors} class provides factory methods for the
71 * executor services provided in this package.
72 *
73 * <h3>Usage Examples</h3>
74 *
75 * Here is a sketch of a network service in which threads in a thread
76 * pool service incoming requests. It uses the preconfigured {@link
77 * Executors#newFixedThreadPool} factory method:
78 *
79 * <pre> {@code
80 * class NetworkService implements Runnable {
81 *   private final ServerSocket serverSocket;
82 *   private final ExecutorService pool;
83 *
84 *   public NetworkService(int port, int poolSize)
85 *       throws IOException {
86 *     serverSocket = new ServerSocket(port);
87 *     pool = Executors.newFixedThreadPool(poolSize);
88 *   }
89 *
90 *   public void run() { // run the service
91 *     try {
92 *       for (;;) {
93 *         pool.execute(new Handler(serverSocket.accept()));
94 *       }
95 *     } catch (IOException ex) {
96 *       pool.shutdown();
97 *     }
98 *   }
99 * }
100 *
101 * class Handler implements Runnable {
102 *   private final Socket socket;
103 *   Handler(Socket socket) { this.socket = socket; }
104 *   public void run() {
105 *     // read and service request on socket
106 *   }
107 * }}</pre>
108 *
109 * The following method shuts down an {@code ExecutorService} in two phases,
110 * first by calling {@code shutdown} to reject incoming tasks, and then
111 * calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:
112 *
113 * <pre> {@code
114 * void shutdownAndAwaitTermination(ExecutorService pool) {
115 *   pool.shutdown(); // Disable new tasks from being submitted
116 *   try {
117 *     // Wait a while for existing tasks to terminate
118 *     if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
119 *       pool.shutdownNow(); // Cancel currently executing tasks
120 *       // Wait a while for tasks to respond to being cancelled
121 *       if (!pool.awaitTermination(60, TimeUnit.SECONDS))
122 *           System.err.println("Pool did not terminate");
123 *     }
124 *   } catch (InterruptedException ie) {
125 *     // (Re-)Cancel if current thread also interrupted
126 *     pool.shutdownNow();
127 *     // Preserve interrupt status
128 *     Thread.currentThread().interrupt();
129 *   }
130 * }}</pre>
131 *
132 * <p>Memory consistency effects: Actions in a thread prior to the
133 * submission of a {@code Runnable} or {@code Callable} task to an
134 * {@code ExecutorService}
135 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
136 * any actions taken by that task, which in turn <i>happen-before</i> the
137 * result is retrieved via {@code Future.get()}.
138 *
139 * @since 1.5
140 * @author Doug Lea
141 */
142public interface ExecutorService extends Executor {
143
144    /**
145     * Initiates an orderly shutdown in which previously submitted
146     * tasks are executed, but no new tasks will be accepted.
147     * Invocation has no additional effect if already shut down.
148     *
149     * <p>This method does not wait for previously submitted tasks to
150     * complete execution.  Use {@link #awaitTermination awaitTermination}
151     * to do that.
152     */
153    void shutdown();
154
155    /**
156     * Attempts to stop all actively executing tasks, halts the
157     * processing of waiting tasks, and returns a list of the tasks
158     * that were awaiting execution.
159     *
160     * <p>This method does not wait for actively executing tasks to
161     * terminate.  Use {@link #awaitTermination awaitTermination} to
162     * do that.
163     *
164     * <p>There are no guarantees beyond best-effort attempts to stop
165     * processing actively executing tasks.  For example, typical
166     * implementations will cancel via {@link Thread#interrupt}, so any
167     * task that fails to respond to interrupts may never terminate.
168     *
169     * @return list of tasks that never commenced execution
170     */
171    List<Runnable> shutdownNow();
172
173    /**
174     * Returns {@code true} if this executor has been shut down.
175     *
176     * @return {@code true} if this executor has been shut down
177     */
178    boolean isShutdown();
179
180    /**
181     * Returns {@code true} if all tasks have completed following shut down.
182     * Note that {@code isTerminated} is never {@code true} unless
183     * either {@code shutdown} or {@code shutdownNow} was called first.
184     *
185     * @return {@code true} if all tasks have completed following shut down
186     */
187    boolean isTerminated();
188
189    /**
190     * Blocks until all tasks have completed execution after a shutdown
191     * request, or the timeout occurs, or the current thread is
192     * interrupted, whichever happens first.
193     *
194     * @param timeout the maximum time to wait
195     * @param unit the time unit of the timeout argument
196     * @return {@code true} if this executor terminated and
197     *         {@code false} if the timeout elapsed before termination
198     * @throws InterruptedException if interrupted while waiting
199     */
200    boolean awaitTermination(long timeout, TimeUnit unit)
201        throws InterruptedException;
202
203    /**
204     * Submits a value-returning task for execution and returns a
205     * Future representing the pending results of the task. The
206     * Future's {@code get} method will return the task's result upon
207     * successful completion.
208     *
209     * <p>
210     * If you would like to immediately block waiting
211     * for a task, you can use constructions of the form
212     * {@code result = exec.submit(aCallable).get();}
213     *
214     * <p>Note: The {@link Executors} class includes a set of methods
215     * that can convert some other common closure-like objects,
216     * for example, {@link java.security.PrivilegedAction} to
217     * {@link Callable} form so they can be submitted.
218     *
219     * @param task the task to submit
220     * @param <T> the type of the task's result
221     * @return a Future representing pending completion of the task
222     * @throws RejectedExecutionException if the task cannot be
223     *         scheduled for execution
224     * @throws NullPointerException if the task is null
225     */
226    <T> Future<T> submit(Callable<T> task);
227
228    /**
229     * Submits a Runnable task for execution and returns a Future
230     * representing that task. The Future's {@code get} method will
231     * return the given result upon successful completion.
232     *
233     * @param task the task to submit
234     * @param result the result to return
235     * @param <T> the type of the result
236     * @return a Future representing pending completion of the task
237     * @throws RejectedExecutionException if the task cannot be
238     *         scheduled for execution
239     * @throws NullPointerException if the task is null
240     */
241    <T> Future<T> submit(Runnable task, T result);
242
243    /**
244     * Submits a Runnable task for execution and returns a Future
245     * representing that task. The Future's {@code get} method will
246     * return {@code null} upon <em>successful</em> completion.
247     *
248     * @param task the task to submit
249     * @return a Future representing pending completion of the task
250     * @throws RejectedExecutionException if the task cannot be
251     *         scheduled for execution
252     * @throws NullPointerException if the task is null
253     */
254    Future<?> submit(Runnable task);
255
256    /**
257     * Executes the given tasks, returning a list of Futures holding
258     * their status and results when all complete.
259     * {@link Future#isDone} is {@code true} for each
260     * element of the returned list.
261     * Note that a <em>completed</em> task could have
262     * terminated either normally or by throwing an exception.
263     * The results of this method are undefined if the given
264     * collection is modified while this operation is in progress.
265     *
266     * @param tasks the collection of tasks
267     * @param <T> the type of the values returned from the tasks
268     * @return a list of Futures representing the tasks, in the same
269     *         sequential order as produced by the iterator for the
270     *         given task list, each of which has completed
271     * @throws InterruptedException if interrupted while waiting, in
272     *         which case unfinished tasks are cancelled
273     * @throws NullPointerException if tasks or any of its elements are {@code null}
274     * @throws RejectedExecutionException if any task cannot be
275     *         scheduled for execution
276     */
277    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
278        throws InterruptedException;
279
280    /**
281     * Executes the given tasks, returning a list of Futures holding
282     * their status and results
283     * when all complete or the timeout expires, whichever happens first.
284     * {@link Future#isDone} is {@code true} for each
285     * element of the returned list.
286     * Upon return, tasks that have not completed are cancelled.
287     * Note that a <em>completed</em> task could have
288     * terminated either normally or by throwing an exception.
289     * The results of this method are undefined if the given
290     * collection is modified while this operation is in progress.
291     *
292     * @param tasks the collection of tasks
293     * @param timeout the maximum time to wait
294     * @param unit the time unit of the timeout argument
295     * @param <T> the type of the values returned from the tasks
296     * @return a list of Futures representing the tasks, in the same
297     *         sequential order as produced by the iterator for the
298     *         given task list. If the operation did not time out,
299     *         each task will have completed. If it did time out, some
300     *         of these tasks will not have completed.
301     * @throws InterruptedException if interrupted while waiting, in
302     *         which case unfinished tasks are cancelled
303     * @throws NullPointerException if tasks, any of its elements, or
304     *         unit are {@code null}
305     * @throws RejectedExecutionException if any task cannot be scheduled
306     *         for execution
307     */
308    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
309                                  long timeout, TimeUnit unit)
310        throws InterruptedException;
311
312    /**
313     * Executes the given tasks, returning the result
314     * of one that has completed successfully (i.e., without throwing
315     * an exception), if any do. Upon normal or exceptional return,
316     * tasks that have not completed are cancelled.
317     * The results of this method are undefined if the given
318     * collection is modified while this operation is in progress.
319     *
320     * @param tasks the collection of tasks
321     * @param <T> the type of the values returned from the tasks
322     * @return the result returned by one of the tasks
323     * @throws InterruptedException if interrupted while waiting
324     * @throws NullPointerException if tasks or any element task
325     *         subject to execution is {@code null}
326     * @throws IllegalArgumentException if tasks is empty
327     * @throws ExecutionException if no task successfully completes
328     * @throws RejectedExecutionException if tasks cannot be scheduled
329     *         for execution
330     */
331    <T> T invokeAny(Collection<? extends Callable<T>> tasks)
332        throws InterruptedException, ExecutionException;
333
334    /**
335     * Executes the given tasks, returning the result
336     * of one that has completed successfully (i.e., without throwing
337     * an exception), if any do before the given timeout elapses.
338     * Upon normal or exceptional return, tasks that have not
339     * completed are cancelled.
340     * The results of this method are undefined if the given
341     * collection is modified while this operation is in progress.
342     *
343     * @param tasks the collection of tasks
344     * @param timeout the maximum time to wait
345     * @param unit the time unit of the timeout argument
346     * @param <T> the type of the values returned from the tasks
347     * @return the result returned by one of the tasks
348     * @throws InterruptedException if interrupted while waiting
349     * @throws NullPointerException if tasks, or unit, or any element
350     *         task subject to execution is {@code null}
351     * @throws TimeoutException if the given timeout elapses before
352     *         any task successfully completes
353     * @throws ExecutionException if no task successfully completes
354     * @throws RejectedExecutionException if tasks cannot be scheduled
355     *         for execution
356     */
357    <T> T invokeAny(Collection<? extends Callable<T>> tasks,
358                    long timeout, TimeUnit unit)
359        throws InterruptedException, ExecutionException, TimeoutException;
360}
361