/*

  * 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

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  */

 /*

  * 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;

 }