/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation.  Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ /* * This file is available under and governed by the GNU General Public * License version 2 only, as published by the Free Software Foundation. * However, the following notice accompanied the original version of this * file: * * 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;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) { *     // (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}<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>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}<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 element task     *         subject to execution is <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, or unit, or any element     *         task subject to execution is <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;}