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.Collection;
import java.util.List;

/**
 * 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:	1.1
Committed:	Sat Mar 26 06:22:50 2016 UTC (8 years, 2 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Log Message:	fork jdk8 maintenance branch for source and jtreg tests
#	User	Rev	Content
1	jsr166	1.1	/*
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.Collection;
10			import java.util.List;
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			}