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.
 *
 * <h2>Usage Examples</h2>
 *
 * 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>
 *
 * An {@code ExecutorService} may also be established and closed
 * (shutdown, blocking until terminated) as follows; illustrating with
 * a different {@code Executors} factory method:
 *
 * <pre> {@code
 * try (ExecutorService e =  Executors.newWorkStealingPool()) {
 *   // submit or execute many tasks with e ...
 * }}</pre>
 *
 * Further customization is also possible. For example, 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 ex) {
 *     // (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, AutoCloseable {

    /**
     * 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;

    /**
     * Initiates an orderly shutdown in which previously submitted tasks are
     * executed, but no new tasks will be accepted. This method waits until all
     * tasks have completed execution and the executor has terminated.
     *
     * <p>If interrupted while waiting, this method stops all executing tasks as
     * if by invoking {@link #shutdownNow()}. It then continues to wait until all
     * actively executing tasks have completed. Tasks that were awaiting
     * execution are not executed. The interrupt status will be re-asserted
     * before this method returns.
     *
     * <p>If already terminated, invoking this method has no effect.
     *
     * @implSpec
     * The default implementation invokes {@code shutdown()} and waits for tasks
     * to complete execution with {@code awaitTermination}.
     *
     * @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.
     * @since 19
     */
    @Override
    default void close() {
        boolean terminated = isTerminated();
        if (!terminated) {
            shutdown();
            boolean interrupted = false;
            while (!terminated) {
                try {
                    terminated = awaitTermination(1L, TimeUnit.DAYS);
                } catch (InterruptedException e) {
                    if (!interrupted) {
                        shutdownNow();
                        interrupted = true;
                    }
                }
            }
            if (interrupted) {
                Thread.currentThread().interrupt();
            }
        }
    }
}
Revision:	1.67
Committed:	Fri Nov 25 16:39:48 2022 UTC (17 months, 3 weeks ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.66:	+2 -2 lines
Log Message:	whitespace
#	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.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	* <h2>Usage Examples</h2>
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	* An {@code ExecutorService} may also be established and closed
77	* (shutdown, blocking until terminated) as follows; illustrating with
78	* a different {@code Executors} factory method:
79	*
80	* <pre> {@code
81	* try (ExecutorService e = Executors.newWorkStealingPool()) {
82	* // submit or execute many tasks with e ...
83	* }}</pre>
84	*
85	* Further customization is also possible. For example, the following
86	* method shuts down an {@code ExecutorService} in two phases, first
87	* by calling {@code shutdown} to reject incoming tasks, and then
88	* calling {@code shutdownNow}, if necessary, to cancel any lingering
89	* tasks:
90	*
91	* <pre> {@code
92	* void shutdownAndAwaitTermination(ExecutorService pool) {
93	* pool.shutdown(); // Disable new tasks from being submitted
94	* try {
95	* // Wait a while for existing tasks to terminate
96	* if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
97	* pool.shutdownNow(); // Cancel currently executing tasks
98	* // Wait a while for tasks to respond to being cancelled
99	* if (!pool.awaitTermination(60, TimeUnit.SECONDS))
100	* System.err.println("Pool did not terminate");
101	* }
102	* } catch (InterruptedException ex) {
103	* // (Re-)Cancel if current thread also interrupted
104	* pool.shutdownNow();
105	* // Preserve interrupt status
106	* Thread.currentThread().interrupt();
107	* }
108	* }}</pre>
109	*
110	* <p>Memory consistency effects: Actions in a thread prior to the
111	* submission of a {@code Runnable} or {@code Callable} task to an
112	* {@code ExecutorService}
113	* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
114	* any actions taken by that task, which in turn <i>happen-before</i> the
115	* result is retrieved via {@code Future.get()}.
116	*
117	* @since 1.5
118	* @author Doug Lea
119	*/
120	public interface ExecutorService extends Executor, AutoCloseable {
121
122	/**
123	* Initiates an orderly shutdown in which previously submitted
124	* tasks are executed, but no new tasks will be accepted.
125	* Invocation has no additional effect if already shut down.
126	*
127	* <p>This method does not wait for previously submitted tasks to
128	* complete execution. Use {@link #awaitTermination awaitTermination}
129	* to do that.
130	*
131	* @throws SecurityException if a security manager exists and
132	* shutting down this ExecutorService may manipulate
133	* threads that the caller is not permitted to modify
134	* because it does not hold {@link
135	* java.lang.RuntimePermission}{@code ("modifyThread")},
136	* or the security manager's {@code checkAccess} method
137	* denies access.
138	*/
139	void shutdown();
140
141	/**
142	* Attempts to stop all actively executing tasks, halts the
143	* processing of waiting tasks, and returns a list of the tasks
144	* that were awaiting execution.
145	*
146	* <p>This method does not wait for actively executing tasks to
147	* terminate. Use {@link #awaitTermination awaitTermination} to
148	* do that.
149	*
150	* <p>There are no guarantees beyond best-effort attempts to stop
151	* processing actively executing tasks. For example, typical
152	* implementations will cancel via {@link Thread#interrupt}, so any
153	* task that fails to respond to interrupts may never terminate.
154	*
155	* @return list of tasks that never commenced execution
156	* @throws SecurityException if a security manager exists and
157	* shutting down this ExecutorService may manipulate
158	* threads that the caller is not permitted to modify
159	* because it does not hold {@link
160	* java.lang.RuntimePermission}{@code ("modifyThread")},
161	* or the security manager's {@code checkAccess} method
162	* denies access.
163	*/
164	List<Runnable> shutdownNow();
165
166	/**
167	* Returns {@code true} if this executor has been shut down.
168	*
169	* @return {@code true} if this executor has been shut down
170	*/
171	boolean isShutdown();
172
173	/**
174	* Returns {@code true} if all tasks have completed following shut down.
175	* Note that {@code isTerminated} is never {@code true} unless
176	* either {@code shutdown} or {@code shutdownNow} was called first.
177	*
178	* @return {@code true} if all tasks have completed following shut down
179	*/
180	boolean isTerminated();
181
182	/**
183	* Blocks until all tasks have completed execution after a shutdown
184	* request, or the timeout occurs, or the current thread is
185	* interrupted, whichever happens first.
186	*
187	* @param timeout the maximum time to wait
188	* @param unit the time unit of the timeout argument
189	* @return {@code true} if this executor terminated and
190	* {@code false} if the timeout elapsed before termination
191	* @throws InterruptedException if interrupted while waiting
192	*/
193	boolean awaitTermination(long timeout, TimeUnit unit)
194	throws InterruptedException;
195
196	/**
197	* Submits a value-returning task for execution and returns a
198	* Future representing the pending results of the task. The
199	* Future's {@code get} method will return the task's result upon
200	* successful completion.
201	*
202	* <p>
203	* If you would like to immediately block waiting
204	* for a task, you can use constructions of the form
205	* {@code result = exec.submit(aCallable).get();}
206	*
207	* <p>Note: The {@link Executors} class includes a set of methods
208	* that can convert some other common closure-like objects,
209	* for example, {@link java.security.PrivilegedAction} to
210	* {@link Callable} form so they can be submitted.
211	*
212	* @param task the task to submit
213	* @param <T> the type of the task's result
214	* @return a Future representing pending completion of the task
215	* @throws RejectedExecutionException if the task cannot be
216	* scheduled for execution
217	* @throws NullPointerException if the task is null
218	*/
219	<T> Future<T> submit(Callable<T> task);
220
221	/**
222	* Submits a Runnable task for execution and returns a Future
223	* representing that task. The Future's {@code get} method will
224	* return the given result upon successful completion.
225	*
226	* @param task the task to submit
227	* @param result the result to return
228	* @param <T> the type of the result
229	* @return a Future representing pending completion of the task
230	* @throws RejectedExecutionException if the task cannot be
231	* scheduled for execution
232	* @throws NullPointerException if the task is null
233	*/
234	<T> Future<T> submit(Runnable task, T result);
235
236	/**
237	* Submits a Runnable task for execution and returns a Future
238	* representing that task. The Future's {@code get} method will
239	* return {@code null} upon <em>successful</em> completion.
240	*
241	* @param task the task to submit
242	* @return a Future representing pending completion of the task
243	* @throws RejectedExecutionException if the task cannot be
244	* scheduled for execution
245	* @throws NullPointerException if the task is null
246	*/
247	Future<?> submit(Runnable task);
248
249	/**
250	* Executes the given tasks, returning a list of Futures holding
251	* their status and results when all complete.
252	* {@link Future#isDone} is {@code true} for each
253	* element of the returned list.
254	* Note that a <em>completed</em> task could have
255	* terminated either normally or by throwing an exception.
256	* The results of this method are undefined if the given
257	* collection is modified while this operation is in progress.
258	*
259	* @param tasks the collection of tasks
260	* @param <T> the type of the values returned from the tasks
261	* @return a list of Futures representing the tasks, in the same
262	* sequential order as produced by the iterator for the
263	* given task list, each of which has completed
264	* @throws InterruptedException if interrupted while waiting, in
265	* which case unfinished tasks are cancelled
266	* @throws NullPointerException if tasks or any of its elements are {@code null}
267	* @throws RejectedExecutionException if any task cannot be
268	* scheduled for execution
269	*/
270	<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
271	throws InterruptedException;
272
273	/**
274	* Executes the given tasks, returning a list of Futures holding
275	* their status and results
276	* when all complete or the timeout expires, whichever happens first.
277	* {@link Future#isDone} is {@code true} for each
278	* element of the returned list.
279	* Upon return, tasks that have not completed are cancelled.
280	* Note that a <em>completed</em> task could have
281	* terminated either normally or by throwing an exception.
282	* The results of this method are undefined if the given
283	* collection is modified while this operation is in progress.
284	*
285	* @param tasks the collection of tasks
286	* @param timeout the maximum time to wait
287	* @param unit the time unit of the timeout argument
288	* @param <T> the type of the values returned from the tasks
289	* @return a list of Futures representing the tasks, in the same
290	* sequential order as produced by the iterator for the
291	* given task list. If the operation did not time out,
292	* each task will have completed. If it did time out, some
293	* of these tasks will not have completed.
294	* @throws InterruptedException if interrupted while waiting, in
295	* which case unfinished tasks are cancelled
296	* @throws NullPointerException if tasks, any of its elements, or
297	* unit are {@code null}
298	* @throws RejectedExecutionException if any task cannot be scheduled
299	* for execution
300	*/
301	<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
302	long timeout, TimeUnit unit)
303	throws InterruptedException;
304
305	/**
306	* Executes the given tasks, returning the result
307	* of one that has completed successfully (i.e., without throwing
308	* an exception), if any do. Upon normal or exceptional return,
309	* tasks that have not completed are cancelled.
310	* The results of this method are undefined if the given
311	* collection is modified while this operation is in progress.
312	*
313	* @param tasks the collection of tasks
314	* @param <T> the type of the values returned from the tasks
315	* @return the result returned by one of the tasks
316	* @throws InterruptedException if interrupted while waiting
317	* @throws NullPointerException if tasks or any element task
318	* subject to execution is {@code null}
319	* @throws IllegalArgumentException if tasks is empty
320	* @throws ExecutionException if no task successfully completes
321	* @throws RejectedExecutionException if tasks cannot be scheduled
322	* for execution
323	*/
324	<T> T invokeAny(Collection<? extends Callable<T>> tasks)
325	throws InterruptedException, ExecutionException;
326
327	/**
328	* Executes the given tasks, returning the result
329	* of one that has completed successfully (i.e., without throwing
330	* an exception), if any do before the given timeout elapses.
331	* Upon normal or exceptional return, tasks that have not
332	* completed are cancelled.
333	* The results of this method are undefined if the given
334	* collection is modified while this operation is in progress.
335	*
336	* @param tasks the collection of tasks
337	* @param timeout the maximum time to wait
338	* @param unit the time unit of the timeout argument
339	* @param <T> the type of the values returned from the tasks
340	* @return the result returned by one of the tasks
341	* @throws InterruptedException if interrupted while waiting
342	* @throws NullPointerException if tasks, or unit, or any element
343	* task subject to execution is {@code null}
344	* @throws TimeoutException if the given timeout elapses before
345	* any task successfully completes
346	* @throws ExecutionException if no task successfully completes
347	* @throws RejectedExecutionException if tasks cannot be scheduled
348	* for execution
349	*/
350	<T> T invokeAny(Collection<? extends Callable<T>> tasks,
351	long timeout, TimeUnit unit)
352	throws InterruptedException, ExecutionException, TimeoutException;
353
354	/**
355	* Initiates an orderly shutdown in which previously submitted tasks are
356	* executed, but no new tasks will be accepted. This method waits until all
357	* tasks have completed execution and the executor has terminated.
358	*
359	* <p>If interrupted while waiting, this method stops all executing tasks as
360	* if by invoking {@link #shutdownNow()}. It then continues to wait until all
361	* actively executing tasks have completed. Tasks that were awaiting
362	* execution are not executed. The interrupt status will be re-asserted
363	* before this method returns.
364	*
365	* <p>If already terminated, invoking this method has no effect.
366	*
367	* @implSpec
368	* The default implementation invokes {@code shutdown()} and waits for tasks
369	* to complete execution with {@code awaitTermination}.
370	*
371	* @throws SecurityException if a security manager exists and
372	* shutting down this ExecutorService may manipulate
373	* threads that the caller is not permitted to modify
374	* because it does not hold {@link
375	* java.lang.RuntimePermission}{@code ("modifyThread")},
376	* or the security manager's {@code checkAccess} method
377	* denies access.
378	* @since 19
379	*/
380	@Override
381	default void close() {
382	boolean terminated = isTerminated();
383	if (!terminated) {
384	shutdown();
385	boolean interrupted = false;
386	while (!terminated) {
387	try {
388	terminated = awaitTermination(1L, TimeUnit.DAYS);
389	} catch (InterruptedException e) {
390	if (!interrupted) {
391	shutdownNow();
392	interrupted = true;
393	}
394	}
395	}
396	if (interrupted) {
397	Thread.currentThread().interrupt();
398	}
399	}
400	}
401	}