util/concurrent/ExecutorService.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent;

import java.util.List;
import java.util.Collection;

/**
 * An {@link Executor} that provides methods to manage termination and
 * methods that can produce a {@link Future} for tracking progress of
 * one or more asynchronous tasks.
 *
 * <p>An {@code ExecutorService} can be shut down, which will cause
 * it to reject new tasks.  Two different methods are provided for
 * shutting down an {@code ExecutorService}. The {@link #shutdown}
 * method will allow previously submitted tasks to execute before
 * terminating, while the {@link #shutdownNow} method prevents waiting
 * tasks from starting and attempts to stop currently executing tasks.
 * Upon termination, an executor has no tasks actively executing, no
 * tasks awaiting execution, and no new tasks can be submitted.  An
 * unused {@code ExecutorService} should be shut down to allow
 * reclamation of its resources.
 *
 * <p>Method {@code submit} extends base method {@link
 * Executor#execute(Runnable)} by creating and returning a {@link Future}
 * that can be used to cancel execution and/or wait for completion.
 * Methods {@code invokeAny} and {@code invokeAll} perform the most
 * commonly useful forms of bulk execution, executing a collection of
 * tasks and then waiting for at least one, or all, to
 * complete. (Class {@link ExecutorCompletionService} can be used to
 * write customized variants of these methods.)
 *
 * <p>The {@link Executors} class provides factory methods for the
 * executor services provided in this package.
 *
 * <h3>Usage Examples</h3>
 *
 * Here is a sketch of a network service in which threads in a thread
 * pool service incoming requests. It uses the preconfigured {@link
 * Executors#newFixedThreadPool} factory method:
 *
 *  <pre> {@code
 * class NetworkService implements Runnable {
 *   private final ServerSocket serverSocket;
 *   private final ExecutorService pool;
 *
 *   public NetworkService(int port, int poolSize)
 *       throws IOException {
 *     serverSocket = new ServerSocket(port);
 *     pool = Executors.newFixedThreadPool(poolSize);
 *   }
 *
 *   public void run() { // run the service
 *     try {
 *       for (;;) {
 *         pool.execute(new Handler(serverSocket.accept()));
 *       }
 *     } catch (IOException ex) {
 *       pool.shutdown();
 *     }
 *   }
 * }
 *
 * class Handler implements Runnable {
 *   private final Socket socket;
 *   Handler(Socket socket) { this.socket = socket; }
 *   public void run() {
 *     // read and service request on socket
 *   }
 * }}</pre>
 *
 * The following method shuts down an {@code ExecutorService} in two phases,
 * first by calling {@code shutdown} to reject incoming tasks, and then
 * calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:
 *
 *  <pre> {@code
 * void shutdownAndAwaitTermination(ExecutorService pool) {
 *   pool.shutdown(); // Disable new tasks from being submitted
 *   try {
 *     // Wait a while for existing tasks to terminate
 *     if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
 *       pool.shutdownNow(); // Cancel currently executing tasks
 *       // Wait a while for tasks to respond to being cancelled
 *       if (!pool.awaitTermination(60, TimeUnit.SECONDS))
 *           System.err.println("Pool did not terminate");
 *     }
 *   } catch (InterruptedException ie) {
 *     // (Re-)Cancel if current thread also interrupted
 *     pool.shutdownNow();
 *     // Preserve interrupt status
 *     Thread.currentThread().interrupt();
 *   }
 * }}</pre>
 *
 * <p>Memory consistency effects: Actions in a thread prior to the
 * submission of a {@code Runnable} or {@code Callable} task to an
 * {@code ExecutorService}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * any actions taken by that task, which in turn <i>happen-before</i> the
 * result is retrieved via {@code Future.get()}.
 *
 * @since 1.5
 * @author Doug Lea
 */
public interface ExecutorService extends Executor {

    /**
     * Initiates an orderly shutdown in which previously submitted
     * tasks are executed, but no new tasks will be accepted.
     * Invocation has no additional effect if already shut down.
     *
     * <p>This method does not wait for previously submitted tasks to
     * complete execution.  Use {@link #awaitTermination awaitTermination}
     * to do that.
     *
     * @throws SecurityException if a security manager exists and
     *         shutting down this ExecutorService may manipulate
     *         threads that the caller is not permitted to modify
     *         because it does not hold {@link
     *         java.lang.RuntimePermission}{@code ("modifyThread")},
     *         or the security manager's {@code checkAccess} method
     *         denies access.
     */
    void shutdown();

    /**
     * Attempts to stop all actively executing tasks, halts the
     * processing of waiting tasks, and returns a list of the tasks
     * that were awaiting execution.
     *
     * <p>This method does not wait for actively executing tasks to
     * terminate.  Use {@link #awaitTermination awaitTermination} to
     * do that.
     *
     * <p>There are no guarantees beyond best-effort attempts to stop
     * processing actively executing tasks.  For example, typical
     * implementations will cancel via {@link Thread#interrupt}, so any
     * task that fails to respond to interrupts may never terminate.
     *
     * @return list of tasks that never commenced execution
     * @throws SecurityException if a security manager exists and
     *         shutting down this ExecutorService may manipulate
     *         threads that the caller is not permitted to modify
     *         because it does not hold {@link
     *         java.lang.RuntimePermission}{@code ("modifyThread")},
     *         or the security manager's {@code checkAccess} method
     *         denies access.
     */
    List<Runnable> shutdownNow();

    /**
     * Returns {@code true} if this executor has been shut down.
     *
     * @return {@code true} if this executor has been shut down
     */
    boolean isShutdown();

    /**
     * Returns {@code true} if all tasks have completed following shut down.
     * Note that {@code isTerminated} is never {@code true} unless
     * either {@code shutdown} or {@code shutdownNow} was called first.
     *
     * @return {@code true} if all tasks have completed following shut down
     */
    boolean isTerminated();

    /**
     * Blocks until all tasks have completed execution after a shutdown
     * request, or the timeout occurs, or the current thread is
     * interrupted, whichever happens first.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @return {@code true} if this executor terminated and
     *         {@code false} if the timeout elapsed before termination
     * @throws InterruptedException if interrupted while waiting
     */
    boolean awaitTermination(long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Submits a value-returning task for execution and returns a
     * Future representing the pending results of the task. The
     * Future's {@code get} method will return the task's result upon
     * successful completion.
     *
     * <p>
     * If you would like to immediately block waiting
     * for a task, you can use constructions of the form
     * {@code result = exec.submit(aCallable).get();}
     *
     * <p>Note: The {@link Executors} class includes a set of methods
     * that can convert some other common closure-like objects,
     * for example, {@link java.security.PrivilegedAction} to
     * {@link Callable} form so they can be submitted.
     *
     * @param task the task to submit
     * @param <T> the type of the task's result
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    <T> Future<T> submit(Callable<T> task);

    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's {@code get} method will
     * return the given result upon successful completion.
     *
     * @param task the task to submit
     * @param result the result to return
     * @param <T> the type of the result
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    <T> Future<T> submit(Runnable task, T result);

    /**
     * Submits a Runnable task for execution and returns a Future
     * representing that task. The Future's {@code get} method will
     * return {@code null} upon <em>successful</em> completion.
     *
     * @param task the task to submit
     * @return a Future representing pending completion of the task
     * @throws RejectedExecutionException if the task cannot be
     *         scheduled for execution
     * @throws NullPointerException if the task is null
     */
    Future<?> submit(Runnable task);

    /**
     * Executes the given tasks, returning a list of Futures holding
     * their status and results when all complete.
     * {@link Future#isDone} is {@code true} for each
     * element of the returned list.
     * Note that a <em>completed</em> task could have
     * terminated either normally or by throwing an exception.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     *
     * @param tasks the collection of tasks
     * @param <T> the type of the values returned from the tasks
     * @return a list of Futures representing the tasks, in the same
     *         sequential order as produced by the iterator for the
     *         given task list, each of which has completed
     * @throws InterruptedException if interrupted while waiting, in
     *         which case unfinished tasks are cancelled
     * @throws NullPointerException if tasks or any of its elements are {@code null}
     * @throws RejectedExecutionException if any task cannot be
     *         scheduled for execution
     */
    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
        throws InterruptedException;

    /**
     * Executes the given tasks, returning a list of Futures holding
     * their status and results
     * when all complete or the timeout expires, whichever happens first.
     * {@link Future#isDone} is {@code true} for each
     * element of the returned list.
     * Upon return, tasks that have not completed are cancelled.
     * Note that a <em>completed</em> task could have
     * terminated either normally or by throwing an exception.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     *
     * @param tasks the collection of tasks
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @param <T> the type of the values returned from the tasks
     * @return a list of Futures representing the tasks, in the same
     *         sequential order as produced by the iterator for the
     *         given task list. If the operation did not time out,
     *         each task will have completed. If it did time out, some
     *         of these tasks will not have completed.
     * @throws InterruptedException if interrupted while waiting, in
     *         which case unfinished tasks are cancelled
     * @throws NullPointerException if tasks, any of its elements, or
     *         unit are {@code null}
     * @throws RejectedExecutionException if any task cannot be scheduled
     *         for execution
     */
    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
                                  long timeout, TimeUnit unit)
        throws InterruptedException;

    /**
     * Executes the given tasks, returning the result
     * of one that has completed successfully (i.e., without throwing
     * an exception), if any do. Upon normal or exceptional return,
     * tasks that have not completed are cancelled.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     *
     * @param tasks the collection of tasks
     * @param <T> the type of the values returned from the tasks
     * @return the result returned by one of the tasks
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks or any element task
     *         subject to execution is {@code null}
     * @throws IllegalArgumentException if tasks is empty
     * @throws ExecutionException if no task successfully completes
     * @throws RejectedExecutionException if tasks cannot be scheduled
     *         for execution
     */
    <T> T invokeAny(Collection<? extends Callable<T>> tasks)
        throws InterruptedException, ExecutionException;

    /**
     * Executes the given tasks, returning the result
     * of one that has completed successfully (i.e., without throwing
     * an exception), if any do before the given timeout elapses.
     * Upon normal or exceptional return, tasks that have not
     * completed are cancelled.
     * The results of this method are undefined if the given
     * collection is modified while this operation is in progress.
     *
     * @param tasks the collection of tasks
     * @param timeout the maximum time to wait
     * @param unit the time unit of the timeout argument
     * @param <T> the type of the values returned from the tasks
     * @return the result returned by one of the tasks
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks, or unit, or any element
     *         task subject to execution is {@code null}
     * @throws TimeoutException if the given timeout elapses before
     *         any task successfully completes
     * @throws ExecutionException if no task successfully completes
     * @throws RejectedExecutionException if tasks cannot be scheduled
     *         for execution
     */
    <T> T invokeAny(Collection<? extends Callable<T>> tasks,
                    long timeout, TimeUnit unit)
        throws InterruptedException, ExecutionException, TimeoutException;
}
Revision:	1.6
Committed:	Sun Jan 18 20:17:32 2015 UTC (9 years, 3 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.5:	+1 -0 lines
Log Message:	exactly one blank line before and after package statements
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent;
8
9	import java.util.List;
10	import java.util.Collection;
11
12	/**
13	* An {@link Executor} that provides methods to manage termination and
14	* methods that can produce a {@link Future} for tracking progress of
15	* one or more asynchronous tasks.
16	*
17	* <p>An {@code ExecutorService} can be shut down, which will cause
18	* it to reject new tasks. Two different methods are provided for
19	* shutting down an {@code ExecutorService}. The {@link #shutdown}
20	* method will allow previously submitted tasks to execute before
21	* terminating, while the {@link #shutdownNow} method prevents waiting
22	* tasks from starting and attempts to stop currently executing tasks.
23	* Upon termination, an executor has no tasks actively executing, no
24	* tasks awaiting execution, and no new tasks can be submitted. An
25	* unused {@code ExecutorService} should be shut down to allow
26	* reclamation of its resources.
27	*
28	* <p>Method {@code submit} extends base method {@link
29	* Executor#execute(Runnable)} by creating and returning a {@link Future}
30	* that can be used to cancel execution and/or wait for completion.
31	* Methods {@code invokeAny} and {@code invokeAll} perform the most
32	* commonly useful forms of bulk execution, executing a collection of
33	* tasks and then waiting for at least one, or all, to
34	* complete. (Class {@link ExecutorCompletionService} can be used to
35	* write customized variants of these methods.)
36	*
37	* <p>The {@link Executors} class provides factory methods for the
38	* executor services provided in this package.
39	*
40	* <h3>Usage Examples</h3>
41	*
42	* Here is a sketch of a network service in which threads in a thread
43	* pool service incoming requests. It uses the preconfigured {@link
44	* Executors#newFixedThreadPool} factory method:
45	*
46	* <pre> {@code
47	* class NetworkService implements Runnable {
48	* private final ServerSocket serverSocket;
49	* private final ExecutorService pool;
50	*
51	* public NetworkService(int port, int poolSize)
52	* throws IOException {
53	* serverSocket = new ServerSocket(port);
54	* pool = Executors.newFixedThreadPool(poolSize);
55	* }
56	*
57	* public void run() { // run the service
58	* try {
59	* for (;;) {
60	* pool.execute(new Handler(serverSocket.accept()));
61	* }
62	* } catch (IOException ex) {
63	* pool.shutdown();
64	* }
65	* }
66	* }
67	*
68	* class Handler implements Runnable {
69	* private final Socket socket;
70	* Handler(Socket socket) { this.socket = socket; }
71	* public void run() {
72	* // read and service request on socket
73	* }
74	* }}</pre>
75	*
76	* The following method shuts down an {@code ExecutorService} in two phases,
77	* first by calling {@code shutdown} to reject incoming tasks, and then
78	* calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:
79	*
80	* <pre> {@code
81	* void shutdownAndAwaitTermination(ExecutorService pool) {
82	* pool.shutdown(); // Disable new tasks from being submitted
83	* try {
84	* // Wait a while for existing tasks to terminate
85	* if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
86	* pool.shutdownNow(); // Cancel currently executing tasks
87	* // Wait a while for tasks to respond to being cancelled
88	* if (!pool.awaitTermination(60, TimeUnit.SECONDS))
89	* System.err.println("Pool did not terminate");
90	* }
91	* } catch (InterruptedException ie) {
92	* // (Re-)Cancel if current thread also interrupted
93	* pool.shutdownNow();
94	* // Preserve interrupt status
95	* Thread.currentThread().interrupt();
96	* }
97	* }}</pre>
98	*
99	* <p>Memory consistency effects: Actions in a thread prior to the
100	* submission of a {@code Runnable} or {@code Callable} task to an
101	* {@code ExecutorService}
102	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
103	* any actions taken by that task, which in turn <i>happen-before</i> the
104	* result is retrieved via {@code Future.get()}.
105	*
106	* @since 1.5
107	* @author Doug Lea
108	*/
109	public interface ExecutorService extends Executor {
110
111	/**
112	* Initiates an orderly shutdown in which previously submitted
113	* tasks are executed, but no new tasks will be accepted.
114	* Invocation has no additional effect if already shut down.
115	*
116	* <p>This method does not wait for previously submitted tasks to
117	* complete execution. Use {@link #awaitTermination awaitTermination}
118	* to do that.
119	*
120	* @throws SecurityException if a security manager exists and
121	* shutting down this ExecutorService may manipulate
122	* threads that the caller is not permitted to modify
123	* because it does not hold {@link
124	* java.lang.RuntimePermission}{@code ("modifyThread")},
125	* or the security manager's {@code checkAccess} method
126	* denies access.
127	*/
128	void shutdown();
129
130	/**
131	* Attempts to stop all actively executing tasks, halts the
132	* processing of waiting tasks, and returns a list of the tasks
133	* that were awaiting execution.
134	*
135	* <p>This method does not wait for actively executing tasks to
136	* terminate. Use {@link #awaitTermination awaitTermination} to
137	* do that.
138	*
139	* <p>There are no guarantees beyond best-effort attempts to stop
140	* processing actively executing tasks. For example, typical
141	* implementations will cancel via {@link Thread#interrupt}, so any
142	* task that fails to respond to interrupts may never terminate.
143	*
144	* @return list of tasks that never commenced execution
145	* @throws SecurityException if a security manager exists and
146	* shutting down this ExecutorService may manipulate
147	* threads that the caller is not permitted to modify
148	* because it does not hold {@link
149	* java.lang.RuntimePermission}{@code ("modifyThread")},
150	* or the security manager's {@code checkAccess} method
151	* denies access.
152	*/
153	List<Runnable> shutdownNow();
154
155	/**
156	* Returns {@code true} if this executor has been shut down.
157	*
158	* @return {@code true} if this executor has been shut down
159	*/
160	boolean isShutdown();
161
162	/**
163	* Returns {@code true} if all tasks have completed following shut down.
164	* Note that {@code isTerminated} is never {@code true} unless
165	* either {@code shutdown} or {@code shutdownNow} was called first.
166	*
167	* @return {@code true} if all tasks have completed following shut down
168	*/
169	boolean isTerminated();
170
171	/**
172	* Blocks until all tasks have completed execution after a shutdown
173	* request, or the timeout occurs, or the current thread is
174	* interrupted, whichever happens first.
175	*
176	* @param timeout the maximum time to wait
177	* @param unit the time unit of the timeout argument
178	* @return {@code true} if this executor terminated and
179	* {@code false} if the timeout elapsed before termination
180	* @throws InterruptedException if interrupted while waiting
181	*/
182	boolean awaitTermination(long timeout, TimeUnit unit)
183	throws InterruptedException;
184
185	/**
186	* Submits a value-returning task for execution and returns a
187	* Future representing the pending results of the task. The
188	* Future's {@code get} method will return the task's result upon
189	* successful completion.
190	*
191	* <p>
192	* If you would like to immediately block waiting
193	* for a task, you can use constructions of the form
194	* {@code result = exec.submit(aCallable).get();}
195	*
196	* <p>Note: The {@link Executors} class includes a set of methods
197	* that can convert some other common closure-like objects,
198	* for example, {@link java.security.PrivilegedAction} to
199	* {@link Callable} form so they can be submitted.
200	*
201	* @param task the task to submit
202	* @param <T> the type of the task's result
203	* @return a Future representing pending completion of the task
204	* @throws RejectedExecutionException if the task cannot be
205	* scheduled for execution
206	* @throws NullPointerException if the task is null
207	*/
208	<T> Future<T> submit(Callable<T> task);
209
210	/**
211	* Submits a Runnable task for execution and returns a Future
212	* representing that task. The Future's {@code get} method will
213	* return the given result upon successful completion.
214	*
215	* @param task the task to submit
216	* @param result the result to return
217	* @param <T> the type of the result
218	* @return a Future representing pending completion of the task
219	* @throws RejectedExecutionException if the task cannot be
220	* scheduled for execution
221	* @throws NullPointerException if the task is null
222	*/
223	<T> Future<T> submit(Runnable task, T result);
224
225	/**
226	* Submits a Runnable task for execution and returns a Future
227	* representing that task. The Future's {@code get} method will
228	* return {@code null} upon <em>successful</em> completion.
229	*
230	* @param task the task to submit
231	* @return a Future representing pending completion of the task
232	* @throws RejectedExecutionException if the task cannot be
233	* scheduled for execution
234	* @throws NullPointerException if the task is null
235	*/
236	Future<?> submit(Runnable task);
237
238	/**
239	* Executes the given tasks, returning a list of Futures holding
240	* their status and results when all complete.
241	* {@link Future#isDone} is {@code true} for each
242	* element of the returned list.
243	* Note that a <em>completed</em> task could have
244	* terminated either normally or by throwing an exception.
245	* The results of this method are undefined if the given
246	* collection is modified while this operation is in progress.
247	*
248	* @param tasks the collection of tasks
249	* @param <T> the type of the values returned from the tasks
250	* @return a list of Futures representing the tasks, in the same
251	* sequential order as produced by the iterator for the
252	* given task list, each of which has completed
253	* @throws InterruptedException if interrupted while waiting, in
254	* which case unfinished tasks are cancelled
255	* @throws NullPointerException if tasks or any of its elements are {@code null}
256	* @throws RejectedExecutionException if any task cannot be
257	* scheduled for execution
258	*/
259	<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
260	throws InterruptedException;
261
262	/**
263	* Executes the given tasks, returning a list of Futures holding
264	* their status and results
265	* when all complete or the timeout expires, whichever happens first.
266	* {@link Future#isDone} is {@code true} for each
267	* element of the returned list.
268	* Upon return, tasks that have not completed are cancelled.
269	* Note that a <em>completed</em> task could have
270	* terminated either normally or by throwing an exception.
271	* The results of this method are undefined if the given
272	* collection is modified while this operation is in progress.
273	*
274	* @param tasks the collection of tasks
275	* @param timeout the maximum time to wait
276	* @param unit the time unit of the timeout argument
277	* @param <T> the type of the values returned from the tasks
278	* @return a list of Futures representing the tasks, in the same
279	* sequential order as produced by the iterator for the
280	* given task list. If the operation did not time out,
281	* each task will have completed. If it did time out, some
282	* of these tasks will not have completed.
283	* @throws InterruptedException if interrupted while waiting, in
284	* which case unfinished tasks are cancelled
285	* @throws NullPointerException if tasks, any of its elements, or
286	* unit are {@code null}
287	* @throws RejectedExecutionException if any task cannot be scheduled
288	* for execution
289	*/
290	<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
291	long timeout, TimeUnit unit)
292	throws InterruptedException;
293
294	/**
295	* Executes the given tasks, returning the result
296	* of one that has completed successfully (i.e., without throwing
297	* an exception), if any do. Upon normal or exceptional return,
298	* tasks that have not completed are cancelled.
299	* The results of this method are undefined if the given
300	* collection is modified while this operation is in progress.
301	*
302	* @param tasks the collection of tasks
303	* @param <T> the type of the values returned from the tasks
304	* @return the result returned by one of the tasks
305	* @throws InterruptedException if interrupted while waiting
306	* @throws NullPointerException if tasks or any element task
307	* subject to execution is {@code null}
308	* @throws IllegalArgumentException if tasks is empty
309	* @throws ExecutionException if no task successfully completes
310	* @throws RejectedExecutionException if tasks cannot be scheduled
311	* for execution
312	*/
313	<T> T invokeAny(Collection<? extends Callable<T>> tasks)
314	throws InterruptedException, ExecutionException;
315
316	/**
317	* Executes the given tasks, returning the result
318	* of one that has completed successfully (i.e., without throwing
319	* an exception), if any do before the given timeout elapses.
320	* Upon normal or exceptional return, tasks that have not
321	* completed are cancelled.
322	* The results of this method are undefined if the given
323	* collection is modified while this operation is in progress.
324	*
325	* @param tasks the collection of tasks
326	* @param timeout the maximum time to wait
327	* @param unit the time unit of the timeout argument
328	* @param <T> the type of the values returned from the tasks
329	* @return the result returned by one of the tasks
330	* @throws InterruptedException if interrupted while waiting
331	* @throws NullPointerException if tasks, or unit, or any element
332	* task subject to execution is {@code null}
333	* @throws TimeoutException if the given timeout elapses before
334	* any task successfully completes
335	* @throws ExecutionException if no task successfully completes
336	* @throws RejectedExecutionException if tasks cannot be scheduled
337	* for execution
338	*/
339	<T> T invokeAny(Collection<? extends Callable<T>> tasks,
340	long timeout, TimeUnit unit)
341	throws InterruptedException, ExecutionException, TimeoutException;
342	}