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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.*;

	/**
	* Provides default implementations of {@link ExecutorService}
	* execution methods. This class implements the {@code submit},
	* {@code invokeAny} and {@code invokeAll} methods using a
	* {@link RunnableFuture} returned by {@code newTaskFor}, which defaults
	* to the {@link FutureTask} class provided in this package. For example,
	* the implementation of {@code submit(Runnable)} creates an
	* associated {@code RunnableFuture} that is executed and
	* returned. Subclasses may override the {@code newTaskFor} methods
	* to return {@code RunnableFuture} implementations other than
	* {@code FutureTask}.
	*
	* <p><b>Extension example</b>. Here is a sketch of a class
	* that customizes {@link ThreadPoolExecutor} to use
	* a {@code CustomTask} class instead of the default {@code FutureTask}:
	* <pre> {@code
	* public class CustomThreadPoolExecutor extends ThreadPoolExecutor {
	*
	* static class CustomTask<V> implements RunnableFuture<V> {...}
	*
	* protected <V> RunnableFuture<V> newTaskFor(Callable<V> c) {
	* return new CustomTask<V>(c);
	* }
	* protected <V> RunnableFuture<V> newTaskFor(Runnable r, V v) {
	* return new CustomTask<V>(r, v);
	* }
	* // ... add constructors, etc.
	* }}</pre>
	*
	* @since 1.5
	* @author Doug Lea
	*/
	public abstract class AbstractExecutorService implements ExecutorService {

	/**
	* Returns a {@code RunnableFuture} for the given runnable and default
	* value.
	*
	* @param runnable the runnable task being wrapped
	* @param value the default value for the returned future
	* @param <T> the type of the given value
	* @return a {@code RunnableFuture} which, when run, will run the
	* underlying runnable and which, as a {@code Future}, will yield
	* the given value as its result and provide for cancellation of
	* the underlying task
	* @since 1.6
	*/
	protected <T> RunnableFuture<T> newTaskFor(Runnable runnable, T value) {
	return new FutureTask<T>(runnable, value);
	}

	/**
	* Returns a {@code RunnableFuture} for the given callable task.
	*
	* @param callable the callable task being wrapped
	* @param <T> the type of the callable's result
	* @return a {@code RunnableFuture} which, when run, will call the
	* underlying callable and which, as a {@code Future}, will yield
	* the callable's result as its result and provide for
	* cancellation of the underlying task
	* @since 1.6
	*/
	protected <T> RunnableFuture<T> newTaskFor(Callable<T> callable) {
	return new FutureTask<T>(callable);
	}

	/**
	* @throws RejectedExecutionException {@inheritDoc}
	* @throws NullPointerException {@inheritDoc}
	*/
	public Future<?> submit(Runnable task) {
	if (task == null) throw new NullPointerException();
	RunnableFuture<Void> ftask = newTaskFor(task, null);
	execute(ftask);
	return ftask;
	}

	/**
	* @throws RejectedExecutionException {@inheritDoc}
	* @throws NullPointerException {@inheritDoc}
	*/
	public <T> Future<T> submit(Runnable task, T result) {
	if (task == null) throw new NullPointerException();
	RunnableFuture<T> ftask = newTaskFor(task, result);
	execute(ftask);
	return ftask;
	}

	/**
	* @throws RejectedExecutionException {@inheritDoc}
	* @throws NullPointerException {@inheritDoc}
	*/
	public <T> Future<T> submit(Callable<T> task) {
	if (task == null) throw new NullPointerException();
	RunnableFuture<T> ftask = newTaskFor(task);
	execute(ftask);
	return ftask;
	}

	/**
	* the main mechanics of invokeAny.
	*/
	private <T> T doInvokeAny(Collection<? extends Callable<T>> tasks,
	boolean timed, long nanos)
	throws InterruptedException, ExecutionException, TimeoutException {
	if (tasks == null)
	throw new NullPointerException();
	int ntasks = tasks.size();
	if (ntasks == 0)
	throw new IllegalArgumentException();
	ArrayList<Future<T>> futures = new ArrayList<Future<T>>(ntasks);
	ExecutorCompletionService<T> ecs =
	new ExecutorCompletionService<T>(this);

	// For efficiency, especially in executors with limited
	// parallelism, check to see if previously submitted tasks are
	// done before submitting more of them. This interleaving
	// plus the exception mechanics account for messiness of main
	// loop.

	try {
	// Record exceptions so that if we fail to obtain any
	// result, we can throw the last exception we got.
	ExecutionException ee = null;
	final long deadline = timed ? System.nanoTime() + nanos : 0L;
	Iterator<? extends Callable<T>> it = tasks.iterator();

	// Start one task for sure; the rest incrementally
	futures.add(ecs.submit(it.next()));
	--ntasks;
	int active = 1;

	for (;;) {
	Future<T> f = ecs.poll();
	if (f == null) {
	if (ntasks > 0) {
	--ntasks;
	futures.add(ecs.submit(it.next()));
	++active;
	}
	else if (active == 0)
	break;
	else if (timed) {
	f = ecs.poll(nanos, TimeUnit.NANOSECONDS);
	if (f == null)
	throw new TimeoutException();
	nanos = deadline - System.nanoTime();
	}
	else
	f = ecs.take();
	}
	if (f != null) {
	--active;
	try {
	return f.get();
	} catch (ExecutionException eex) {
	ee = eex;
	} catch (RuntimeException rex) {
	ee = new ExecutionException(rex);
	}
	}
	}

	if (ee == null)
	ee = new ExecutionException();
	throw ee;

	} finally {
	for (int i = 0, size = futures.size(); i < size; i++)
	futures.get(i).cancel(true);
	}
	}

	public <T> T invokeAny(Collection<? extends Callable<T>> tasks)
	throws InterruptedException, ExecutionException {
	try {
	return doInvokeAny(tasks, false, 0);
	} catch (TimeoutException cannotHappen) {
	assert false;
	return null;
	}
	}

	public <T> T invokeAny(Collection<? extends Callable<T>> tasks,
	long timeout, TimeUnit unit)
	throws InterruptedException, ExecutionException, TimeoutException {
	return doInvokeAny(tasks, true, unit.toNanos(timeout));
	}

	public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
	throws InterruptedException {
	if (tasks == null)
	throw new NullPointerException();
	ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
	boolean done = false;
	try {
	for (Callable<T> t : tasks) {
	RunnableFuture<T> f = newTaskFor(t);
	futures.add(f);
	execute(f);
	}
	for (int i = 0, size = futures.size(); i < size; i++) {
	Future<T> f = futures.get(i);
	if (!f.isDone()) {
	try {
	f.get();
	} catch (CancellationException ignore) {
	} catch (ExecutionException ignore) {
	}
	}
	}
	done = true;
	return futures;
	} finally {
	if (!done)
	for (int i = 0, size = futures.size(); i < size; i++)
	futures.get(i).cancel(true);
	}
	}

	public <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks,
	long timeout, TimeUnit unit)
	throws InterruptedException {
	if (tasks == null)
	throw new NullPointerException();
	long nanos = unit.toNanos(timeout);
	ArrayList<Future<T>> futures = new ArrayList<Future<T>>(tasks.size());
	boolean done = false;
	try {
	for (Callable<T> t : tasks)
	futures.add(newTaskFor(t));

	final long deadline = System.nanoTime() + nanos;
	final int size = futures.size();

	// Interleave time checks and calls to execute in case
	// executor doesn't have any/much parallelism.
	for (int i = 0; i < size; i++) {
	execute((Runnable)futures.get(i));
	nanos = deadline - System.nanoTime();
	if (nanos <= 0L)
	return futures;
	}

	for (int i = 0; i < size; i++) {
	Future<T> f = futures.get(i);
	if (!f.isDone()) {
	if (nanos <= 0L)
	return futures;
	try {
	f.get(nanos, TimeUnit.NANOSECONDS);
	} catch (CancellationException ignore) {
	} catch (ExecutionException ignore) {
	} catch (TimeoutException toe) {
	return futures;
	}
	nanos = deadline - System.nanoTime();
	}
	}
	done = true;
	return futures;
	} finally {
	if (!done)
	for (int i = 0, size = futures.size(); i < size; i++)
	futures.get(i).cancel(true);
	}
	}

	}

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