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/licenses/publicdomain
 */

package java.util.concurrent;
import java.util.List;
import java.util.Collection;
import java.security.PrivilegedAction;
import java.security.PrivilegedExceptionAction;

/**
 * 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 <tt>ExecutorService</tt> can be shut down, which will cause
 * it to reject new tasks.  Two different methods are provided for
 * shutting down an <tt>ExecutorService</tt>. 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 <tt>ExecutorService</tt> should be shut down to allow
 * reclamation of its resources.
 *
 * <p> Method <tt>submit</tt> extends base method {@link
 * Executor#execute} by creating and returning a {@link Future} that
 * can be used to cancel execution and/or wait for completion.
 * Methods <tt>invokeAny</tt> and <tt>invokeAll</tt> 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>
 * 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 <tt>ExecutorService</tt> in two phases,
 * first by calling <tt>shutdown</tt> to reject incoming tasks, and then
 * calling <tt>shutdownNow</tt>, if necessary, to cancel any lingering tasks:
 *
 * <pre>
 * 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) {
 *     pool.shutdownNow(); // (Re-)Cancel if current thread also interrupted
 *     Thread.currentThread().interrupt(); // Preserve interrupt status
 *   }
 * }
 * </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.
     *
     * @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}<tt>("modifyThread")</tt>,
     *         or the security manager's <tt>checkAccess</tt> 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>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}<tt>("modifyThread")</tt>,
     *         or the security manager's <tt>checkAccess</tt> method
     *         denies access.
     */
    List<Runnable> shutdownNow();

    /**
     * Returns <tt>true</tt> if this executor has been shut down.
     *
     * @return <tt>true</tt> if this executor has been shut down
     */
    boolean isShutdown();

    /**
     * Returns <tt>true</tt> if all tasks have completed following shut down.
     * Note that <tt>isTerminated</tt> is never <tt>true</tt> unless
     * either <tt>shutdown</tt> or <tt>shutdownNow</tt> was called first.
     *
     * @return <tt>true</tt> 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 <tt>true</tt> if this executor terminated and
     *         <tt>false</tt> 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 <tt>get</tt> 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
     * <tt>result = exec.submit(aCallable).get();</tt>
     *
     * <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
     * @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 <tt>get</tt> method will
     * return the given result upon successful completion.
     *
     * @param task the task to submit
     * @param result the result to return
     * @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 <tt>get</tt> method will
     * return <tt>null</tt> 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 <tt>true</tt> 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
     * @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 <tt>null</tt>
     * @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 <tt>true</tt> 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
     * @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 <tt>null</tt>
     * @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
     * @return the result returned by one of the tasks
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks or any of its elements
     *         are <tt>null</tt>
     * @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
     * @return the result returned by one of the tasks.
     * @throws InterruptedException if interrupted while waiting
     * @throws NullPointerException if tasks, any of its elements, or
     *         unit are <tt>null</tt>
     * @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:	1.47
Committed:	Fri Jul 14 11:01:44 2006 UTC (17 years, 11 months ago) by dl
Branch:	MAIN
Changes since 1.46:	+36 -11 lines
Log Message:	Improve documentation about shutdown
#	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/licenses/publicdomain
5	*/
6
7	package java.util.concurrent;
8	import java.util.List;
9	import java.util.Collection;
10	import java.security.PrivilegedAction;
11	import java.security.PrivilegedExceptionAction;
12
13	/**
14	* An {@link Executor} that provides methods to manage termination and
15	* methods that can produce a {@link Future} for tracking progress of
16	* one or more asynchronous tasks.
17	*
18	* <p> An <tt>ExecutorService</tt> can be shut down, which will cause
19	* it to reject new tasks. Two different methods are provided for
20	* shutting down an <tt>ExecutorService</tt>. The {@link #shutdown}
21	* method will allow previously submitted tasks to execute before
22	* terminating, while the {@link #shutdownNow} method prevents waiting
23	* tasks from starting and attempts to stop currently executing tasks.
24	* Upon termination, an executor has no tasks actively executing, no
25	* tasks awaiting execution, and no new tasks can be submitted. An
26	* unused <tt>ExecutorService</tt> should be shut down to allow
27	* reclamation of its resources.
28	*
29	* <p> Method <tt>submit</tt> extends base method {@link
30	* Executor#execute} by creating and returning a {@link Future} that
31	* can be used to cancel execution and/or wait for completion.
32	* Methods <tt>invokeAny</tt> and <tt>invokeAll</tt> perform the most
33	* commonly useful forms of bulk execution, executing a collection of
34	* tasks and then waiting for at least one, or all, to
35	* complete. (Class {@link ExecutorCompletionService} can be used to
36	* write customized variants of these methods.)
37	*
38	* <p>The {@link Executors} class provides factory methods for the
39	* executor services provided in this package.
40	*
41	* <h3>Usage Examples</h3>
42	*
43	* Here is a sketch of a network service in which threads in a thread
44	* pool service incoming requests. It uses the preconfigured {@link
45	* Executors#newFixedThreadPool} factory method:
46	*
47	* <pre>
48	* class NetworkService implements Runnable {
49	* private final ServerSocket serverSocket;
50	* private final ExecutorService pool;
51	*
52	* public NetworkService(int port, int poolSize)
53	* throws IOException {
54	* serverSocket = new ServerSocket(port);
55	* pool = Executors.newFixedThreadPool(poolSize);
56	* }
57	*
58	* public void run() { // run the service
59	* try {
60	* for (;;) {
61	* pool.execute(new Handler(serverSocket.accept()));
62	* }
63	* } catch (IOException ex) {
64	* pool.shutdown();
65	* }
66	* }
67	* }
68	*
69	* class Handler implements Runnable {
70	* private final Socket socket;
71	* Handler(Socket socket) { this.socket = socket; }
72	* public void run() {
73	* // read and service request on socket
74	* }
75	* }
76	* </pre>
77	*
78	* The following method shuts down an <tt>ExecutorService</tt> in two phases,
79	* first by calling <tt>shutdown</tt> to reject incoming tasks, and then
80	* calling <tt>shutdownNow</tt>, if necessary, to cancel any lingering tasks:
81	*
82	* <pre>
83	* void shutdownAndAwaitTermination(ExecutorService pool) {
84	* pool.shutdown(); // Disable new tasks from being submitted
85	* try {
86	* // Wait a while for existing tasks to terminate
87	* if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
88	* pool.shutdownNow(); // Cancel currently executing tasks
89	* // Wait a while for tasks to respond to being cancelled
90	* if (!pool.awaitTermination(60, TimeUnit.SECONDS))
91	* System.err.println("Pool did not terminate");
92	* }
93	* } catch (InterruptedException ie) {
94	* pool.shutdownNow(); // (Re-)Cancel if current thread also interrupted
95	* Thread.currentThread().interrupt(); // Preserve interrupt status
96	* }
97	* }
98	* </pre>
99	*
100	* <p>Memory consistency effects: Actions in a thread prior to the
101	* submission of a {@code Runnable} or {@code Callable} task to an
102	* {@code ExecutorService}
103	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
104	* any actions taken by that task, which in turn <i>happen-before</i> the
105	* result is retrieved via {@code Future.get()}.
106	*
107	* @since 1.5
108	* @author Doug Lea
109	*/
110	public interface ExecutorService extends Executor {
111
112	/**
113	* Initiates an orderly shutdown in which previously submitted
114	* tasks are executed, but no new tasks will be accepted.
115	* Invocation has no additional effect if already shut down.
116	*
117	* @throws SecurityException if a security manager exists and
118	* shutting down this ExecutorService may manipulate
119	* threads that the caller is not permitted to modify
120	* because it does not hold {@link
121	* java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
122	* or the security manager's <tt>checkAccess</tt> method
123	* denies access.
124	*/
125	void shutdown();
126
127	/**
128	* Attempts to stop all actively executing tasks, halts the
129	* processing of waiting tasks, and returns a list of the tasks that were
130	* awaiting execution.
131	*
132	* <p>There are no guarantees beyond best-effort attempts to stop
133	* processing actively executing tasks. For example, typical
134	* implementations will cancel via {@link Thread#interrupt}, so any
135	* task that fails to respond to interrupts may never terminate.
136	*
137	* @return list of tasks that never commenced execution
138	* @throws SecurityException if a security manager exists and
139	* shutting down this ExecutorService may manipulate
140	* threads that the caller is not permitted to modify
141	* because it does not hold {@link
142	* java.lang.RuntimePermission}<tt>("modifyThread")</tt>,
143	* or the security manager's <tt>checkAccess</tt> method
144	* denies access.
145	*/
146	List<Runnable> shutdownNow();
147
148	/**
149	* Returns <tt>true</tt> if this executor has been shut down.
150	*
151	* @return <tt>true</tt> if this executor has been shut down
152	*/
153	boolean isShutdown();
154
155	/**
156	* Returns <tt>true</tt> if all tasks have completed following shut down.
157	* Note that <tt>isTerminated</tt> is never <tt>true</tt> unless
158	* either <tt>shutdown</tt> or <tt>shutdownNow</tt> was called first.
159	*
160	* @return <tt>true</tt> if all tasks have completed following shut down
161	*/
162	boolean isTerminated();
163
164	/**
165	* Blocks until all tasks have completed execution after a shutdown
166	* request, or the timeout occurs, or the current thread is
167	* interrupted, whichever happens first.
168	*
169	* @param timeout the maximum time to wait
170	* @param unit the time unit of the timeout argument
171	* @return <tt>true</tt> if this executor terminated and
172	* <tt>false</tt> if the timeout elapsed before termination
173	* @throws InterruptedException if interrupted while waiting
174	*/
175	boolean awaitTermination(long timeout, TimeUnit unit)
176	throws InterruptedException;
177
178
179	/**
180	* Submits a value-returning task for execution and returns a
181	* Future representing the pending results of the task. The
182	* Future's <tt>get</tt> method will return the task's result upon
183	* successful completion.
184	*
185	* <p>
186	* If you would like to immediately block waiting
187	* for a task, you can use constructions of the form
188	* <tt>result = exec.submit(aCallable).get();</tt>
189	*
190	* <p> Note: The {@link Executors} class includes a set of methods
191	* that can convert some other common closure-like objects,
192	* for example, {@link java.security.PrivilegedAction} to
193	* {@link Callable} form so they can be submitted.
194	*
195	* @param task the task to submit
196	* @return a Future representing pending completion of the task
197	* @throws RejectedExecutionException if the task cannot be
198	* scheduled for execution
199	* @throws NullPointerException if the task is null
200	*/
201	<T> Future<T> submit(Callable<T> task);
202
203	/**
204	* Submits a Runnable task for execution and returns a Future
205	* representing that task. The Future's <tt>get</tt> method will
206	* return the given result upon successful completion.
207	*
208	* @param task the task to submit
209	* @param result the result to return
210	* @return a Future representing pending completion of the task
211	* @throws RejectedExecutionException if the task cannot be
212	* scheduled for execution
213	* @throws NullPointerException if the task is null
214	*/
215	<T> Future<T> submit(Runnable task, T result);
216
217	/**
218	* Submits a Runnable task for execution and returns a Future
219	* representing that task. The Future's <tt>get</tt> method will
220	* return <tt>null</tt> upon <em>successful</em> completion.
221	*
222	* @param task the task to submit
223	* @return a Future representing pending completion of the task
224	* @throws RejectedExecutionException if the task cannot be
225	* scheduled for execution
226	* @throws NullPointerException if the task is null
227	*/
228	Future<?> submit(Runnable task);
229
230	/**
231	* Executes the given tasks, returning a list of Futures holding
232	* their status and results when all complete.
233	* {@link Future#isDone} is <tt>true</tt> for each
234	* element of the returned list.
235	* Note that a <em>completed</em> task could have
236	* terminated either normally or by throwing an exception.
237	* The results of this method are undefined if the given
238	* collection is modified while this operation is in progress.
239	*
240	* @param tasks the collection of tasks
241	* @return A list of Futures representing the tasks, in the same
242	* sequential order as produced by the iterator for the
243	* given task list, each of which has completed.
244	* @throws InterruptedException if interrupted while waiting, in
245	* which case unfinished tasks are cancelled.
246	* @throws NullPointerException if tasks or any of its elements are <tt>null</tt>
247	* @throws RejectedExecutionException if any task cannot be
248	* scheduled for execution
249	*/
250
251	<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
252	throws InterruptedException;
253
254	/**
255	* Executes the given tasks, returning a list of Futures holding
256	* their status and results
257	* when all complete or the timeout expires, whichever happens first.
258	* {@link Future#isDone} is <tt>true</tt> for each
259	* element of the returned list.
260	* Upon return, tasks that have not completed are cancelled.
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 timeout the maximum time to wait
268	* @param unit the time unit of the timeout argument
269	* @return a list of Futures representing the tasks, in the same
270	* sequential order as produced by the iterator for the
271	* given task list. If the operation did not time out,
272	* each task will have completed. If it did time out, some
273	* of these tasks will not have completed.
274	* @throws InterruptedException if interrupted while waiting, in
275	* which case unfinished tasks are cancelled
276	* @throws NullPointerException if tasks, any of its elements, or
277	* unit are <tt>null</tt>
278	* @throws RejectedExecutionException if any task cannot be scheduled
279	* for execution
280	*/
281	<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
282	long timeout, TimeUnit unit)
283	throws InterruptedException;
284
285	/**
286	* Executes the given tasks, returning the result
287	* of one that has completed successfully (i.e., without throwing
288	* an exception), if any do. Upon normal or exceptional return,
289	* tasks that have not completed are cancelled.
290	* The results of this method are undefined if the given
291	* collection is modified while this operation is in progress.
292	*
293	* @param tasks the collection of tasks
294	* @return the result returned by one of the tasks
295	* @throws InterruptedException if interrupted while waiting
296	* @throws NullPointerException if tasks or any of its elements
297	* are <tt>null</tt>
298	* @throws IllegalArgumentException if tasks is empty
299	* @throws ExecutionException if no task successfully completes
300	* @throws RejectedExecutionException if tasks cannot be scheduled
301	* for execution
302	*/
303	<T> T invokeAny(Collection<? extends Callable<T>> tasks)
304	throws InterruptedException, ExecutionException;
305
306	/**
307	* Executes the given tasks, returning the result
308	* of one that has completed successfully (i.e., without throwing
309	* an exception), if any do before the given timeout elapses.
310	* Upon normal or exceptional return, tasks that have not
311	* completed are cancelled.
312	* The results of this method are undefined if the given
313	* collection is modified while this operation is in progress.
314	*
315	* @param tasks the collection of tasks
316	* @param timeout the maximum time to wait
317	* @param unit the time unit of the timeout argument
318	* @return the result returned by one of the tasks.
319	* @throws InterruptedException if interrupted while waiting
320	* @throws NullPointerException if tasks, any of its elements, or
321	* unit are <tt>null</tt>
322	* @throws TimeoutException if the given timeout elapses before
323	* any task successfully completes
324	* @throws ExecutionException if no task successfully completes
325	* @throws RejectedExecutionException if tasks cannot be scheduled
326	* for execution
327	*/
328	<T> T invokeAny(Collection<? extends Callable<T>> tasks,
329	long timeout, TimeUnit unit)
330	throws InterruptedException, ExecutionException, TimeoutException;
331	}