/*

 * 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.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.

 *

 *

 * Here is a sketch of a network service in which threads in a thread

 * pool service incoming requests. It uses the preconfigured {@link

 * Executors#newFixedThreadPool} factory method:

 *

 * <pre> {@code

 * class NetworkService implements Runnable {

 *   private final ServerSocket serverSocket;

 *   private final ExecutorService pool;

 *

 *   public NetworkService(int port, int poolSize)

 *       throws IOException {

 *     serverSocket = new ServerSocket(port);

 *     pool = Executors.newFixedThreadPool(poolSize);

 *   }

 *

 *   public void run() { // run the service

 *     try {

 *       for (;;) {

 *         pool.execute(new Handler(serverSocket.accept()));

 *       }

 *     } catch (IOException ex) {

 *       pool.shutdown();

 *     }

 *   }

 * }

 *

 * class Handler implements Runnable {

 *   private final Socket socket;

 *   Handler(Socket socket) { this.socket = socket; }

 *   public void run() {

 *     // read and service request on socket

 *   }

 * }}</pre>

 *

 * The following method shuts down an {@code ExecutorService} in two phases,

 * first by calling {@code shutdown} to reject incoming tasks, and then

 * calling {@code shutdownNow}, if necessary, to cancel any lingering tasks:

 *

 * <pre> {@code

 * void shutdownAndAwaitTermination(ExecutorService pool) {

 *   pool.shutdown(); // Disable new tasks from being submitted

 *   try {

 *     // Wait a while for existing tasks to terminate

 *     if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {

 *       pool.shutdownNow(); // Cancel currently executing tasks

 *       // Wait a while for tasks to respond to being cancelled

 *       if (!pool.awaitTermination(60, TimeUnit.SECONDS))

 *           System.err.println("Pool did not terminate");

 *     }

 *   } catch (InterruptedException ie) {

 *     // (Re-)Cancel if current thread also interrupted

 *     pool.shutdownNow();

 *     // Preserve interrupt status

 *     Thread.currentThread().interrupt();

 *   }

 * }}</pre>

 *

 * <p>Memory consistency effects: Actions in a thread prior to the

 * submission of a {@code Runnable} or {@code Callable} task to an

 * {@code ExecutorService}

 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>

 * any actions taken by that task, which in turn <i>happen-before</i> the

 * result is retrieved via {@code Future.get()}.

 *

 * @since 1.5

 * @author Doug Lea

 */

public interface ExecutorService extends Executor {

    /**

     * Initiates an orderly shutdown in which previously submitted

     * tasks are executed, but no new tasks will be accepted.

     * Invocation has no additional effect if already shut down.

     *

     * <p>This method does not wait for previously submitted tasks to

     * complete execution.  Use {@link #awaitTermination awaitTermination}

     * to do that.

     *

     * @throws SecurityException if a security manager exists and

     *         shutting down this ExecutorService may manipulate

     *         threads that the caller is not permitted to modify

     *         because it does not hold {@link

     *         java.lang.RuntimePermission}{@code ("modifyThread")},

     *         or the security manager's {@code checkAccess} method

     *         denies access.

     */

    void shutdown();

    /**

     * Attempts to stop all actively executing tasks, halts the

     * processing of waiting tasks, and returns a list of the tasks

     * that were awaiting execution.

     *

     * <p>This method does not wait for actively executing tasks to

     * terminate.  Use {@link #awaitTermination awaitTermination} to

     * do that.

     *

     * <p>There are no guarantees beyond best-effort attempts to stop

     * processing actively executing tasks.  For example, typical

     * implementations will cancel via {@link Thread#interrupt}, so any

     * task that fails to respond to interrupts may never terminate.

     *

     * @return list of tasks that never commenced execution

     * @throws SecurityException if a security manager exists and

     *         shutting down this ExecutorService may manipulate

     *         threads that the caller is not permitted to modify

     *         because it does not hold {@link

     *         java.lang.RuntimePermission}{@code ("modifyThread")},

     *         or the security manager's {@code checkAccess} method

     *         denies access.

     */

    List<Runnable> shutdownNow();

    /**

     * Returns {@code true} if this executor has been shut down.

     *

     * @return {@code true} if this executor has been shut down

     */

    boolean isShutdown();

    /**

     * Returns {@code true} if all tasks have completed following shut down.

     * Note that {@code isTerminated} is never {@code true} unless

     * either {@code shutdown} or {@code shutdownNow} was called first.

     *

     * @return {@code true} if all tasks have completed following shut down

     */

    boolean isTerminated();

    /**

     * Blocks until all tasks have completed execution after a shutdown

     * request, or the timeout occurs, or the current thread is

     * interrupted, whichever happens first.

     *

     * @param timeout the maximum time to wait

     * @param unit the time unit of the timeout argument

     * @return {@code true} if this executor terminated and

     *         {@code false} if the timeout elapsed before termination

     * @throws InterruptedException if interrupted while waiting

     */

    boolean awaitTermination(long timeout, TimeUnit unit)

        throws InterruptedException;

    /**

     * Submits a value-returning task for execution and returns a

     * Future representing the pending results of the task. The

     * Future's {@code get} method will return the task's result upon

     * successful completion.

     *

     * <p>

     * If you would like to immediately block waiting

     * for a task, you can use constructions of the form

     * {@code result = exec.submit(aCallable).get();}

     *

     * <p>Note: The {@link Executors} class includes a set of methods

     * that can convert some other common closure-like objects,

     * for example, {@link java.security.PrivilegedAction} to

     * {@link Callable} form so they can be submitted.

     *

     * @param task the task to submit

     * @param <T> the type of the task's result

     * @return a Future representing pending completion of the task

     * @throws RejectedExecutionException if the task cannot be

     *         scheduled for execution

     * @throws NullPointerException if the task is null

     */

    <T> Future<T> submit(Callable<T> task);

    /**

     * Submits a Runnable task for execution and returns a Future

     * representing that task. The Future's {@code get} method will

     * return the given result upon successful completion.

     *

     * @param task the task to submit

     * @param result the result to return

     * @param <T> the type of the result

     * @return a Future representing pending completion of the task

     * @throws RejectedExecutionException if the task cannot be

     *         scheduled for execution

     * @throws NullPointerException if the task is null

     */

    <T> Future<T> submit(Runnable task, T result);

    /**

     * Submits a Runnable task for execution and returns a Future

     * representing that task. The Future's {@code get} method will

     * return {@code null} upon <em>successful</em> completion.

     *

     * @param task the task to submit

     * @return a Future representing pending completion of the task

     * @throws RejectedExecutionException if the task cannot be

     *         scheduled for execution

     * @throws NullPointerException if the task is null

     */

    Future<?> submit(Runnable task);

    /**

     * Executes the given tasks, returning a list of Futures holding

     * their status and results when all complete.

     * {@link Future#isDone} is {@code true} for each

     * element of the returned list.

     * Note that a <em>completed</em> task could have

     * terminated either normally or by throwing an exception.

     * The results of this method are undefined if the given

     * collection is modified while this operation is in progress.

     *

     * @param tasks the collection of tasks

     * @param <T> the type of the values returned from the tasks

     * @return a list of Futures representing the tasks, in the same

     *         sequential order as produced by the iterator for the

     *         given task list, each of which has completed

     * @throws InterruptedException if interrupted while waiting, in

     *         which case unfinished tasks are cancelled

     * @throws NullPointerException if tasks or any of its elements are {@code null}

     * @throws RejectedExecutionException if any task cannot be

     *         scheduled for execution

     */

    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)

        throws InterruptedException;

    /**

     * Executes the given tasks, returning a list of Futures holding

     * their status and results

     * when all complete or the timeout expires, whichever happens first.

     * {@link Future#isDone} is {@code true} for each

     * element of the returned list.

     * Upon return, tasks that have not completed are cancelled.

     * Note that a <em>completed</em> task could have

     * terminated either normally or by throwing an exception.

     * The results of this method are undefined if the given

     * collection is modified while this operation is in progress.

     *

     * @param tasks the collection of tasks

     * @param timeout the maximum time to wait

     * @param unit the time unit of the timeout argument

     * @param <T> the type of the values returned from the tasks

     * @return a list of Futures representing the tasks, in the same

     *         sequential order as produced by the iterator for the

     *         given task list. If the operation did not time out,

     *         each task will have completed. If it did time out, some

     *         of these tasks will not have completed.

     * @throws InterruptedException if interrupted while waiting, in

     *         which case unfinished tasks are cancelled

     * @throws NullPointerException if tasks, any of its elements, or

     *         unit are {@code null}

     * @throws RejectedExecutionException if any task cannot be scheduled

     *         for execution

     */

    <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,

                                  long timeout, TimeUnit unit)

        throws InterruptedException;

    /**

     * Executes the given tasks, returning the result

     * of one that has completed successfully (i.e., without throwing

     * an exception), if any do. Upon normal or exceptional return,

     * tasks that have not completed are cancelled.

     * The results of this method are undefined if the given

     * collection is modified while this operation is in progress.

     *

     * @param tasks the collection of tasks

     * @param <T> the type of the values returned from the tasks

     * @return the result returned by one of the tasks

     * @throws InterruptedException if interrupted while waiting

     * @throws NullPointerException if tasks or any element task

     *         subject to execution is {@code null}

     * @throws IllegalArgumentException if tasks is empty

     * @throws ExecutionException if no task successfully completes

     * @throws RejectedExecutionException if tasks cannot be scheduled

     *         for execution

     */

    <T> T invokeAny(Collection<? extends Callable<T>> tasks)

        throws InterruptedException, ExecutionException;

    /**

     * Executes the given tasks, returning the result

     * of one that has completed successfully (i.e., without throwing

     * an exception), if any do before the given timeout elapses.

     * Upon normal or exceptional return, tasks that have not

     * completed are cancelled.

     * The results of this method are undefined if the given

     * collection is modified while this operation is in progress.

     *

     * @param tasks the collection of tasks

     * @param timeout the maximum time to wait

     * @param unit the time unit of the timeout argument

     * @param <T> the type of the values returned from the tasks

     * @return the result returned by one of the tasks

     * @throws InterruptedException if interrupted while waiting

     * @throws NullPointerException if tasks, or unit, or any element

     *         task subject to execution is {@code null}

     * @throws TimeoutException if the given timeout elapses before

     *         any task successfully completes

     * @throws ExecutionException if no task successfully completes

     * @throws RejectedExecutionException if tasks cannot be scheduled

     *         for execution

     */

    <T> T invokeAny(Collection<? extends Callable<T>> tasks,

                    long timeout, TimeUnit unit)

        throws InterruptedException, ExecutionException, TimeoutException;

}