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	/*
	* 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;

	/**
	* 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.
	*
	* <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> {@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;
	}

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