/*

 * 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 static java.util.concurrent.TimeUnit.NANOSECONDS;

import java.util.ArrayList;

import java.util.Collection;

import java.util.Iterator;

import java.util.List;

/**

 * 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<>(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, 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 {

            cancelAll(futures);

        }

    }

    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<>(tasks.size());

        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) {}

                }

            }

            return futures;

        } catch (Throwable t) {

            cancelAll(futures);

            throw t;

        }

    }

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

                                         long timeout, TimeUnit unit)

        throws InterruptedException {

        if (tasks == null)

            throw new NullPointerException();

        final long nanos = unit.toNanos(timeout);

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

        ArrayList<Future<T>> futures = new ArrayList<>(tasks.size());

        int j = 0;

        timedOut: try {

            for (Callable<T> t : tasks)

                futures.add(newTaskFor(t));

            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++) {

                if (((i == 0) ? nanos : deadline - System.nanoTime()) <= 0L)

                    break timedOut;

                execute((Runnable)futures.get(i));

            }

            for (; j < size; j++) {

                Future<T> f = futures.get(j);

                if (!f.isDone()) {

                    try { f.get(deadline - System.nanoTime(), NANOSECONDS); }

                    catch (CancellationException ignore) {}

                    catch (ExecutionException ignore) {}

                    catch (TimeoutException timedOut) {

                        break timedOut;

                    }

                }

            }

            return futures;

        } catch (Throwable t) {

            cancelAll(futures);

            throw t;

        }

        // Timed out before all the tasks could be completed; cancel remaining

        cancelAll(futures, j);

        return futures;

    }

    private static <T> void cancelAll(ArrayList<Future<T>> futures) {

        cancelAll(futures, 0);

    }

    /** Cancels all futures with index at least j. */

    private static <T> void cancelAll(ArrayList<Future<T>> futures, int j) {

        for (int size = futures.size(); j < size; j++)

            futures.get(j).cancel(true);

    }

}