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/*

 * 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/licenses/publicdomain

 */

package java.util.concurrent;

import java.util.*;

/**

 * Provides default implementations of {@link ExecutorService}

 * execution methods. This class implements the <tt>submit</tt>,

 * <tt>invokeAny</tt> and <tt>invokeAll</tt> methods using a

 * {@link RunnableFuture} returned by <tt>newTaskFor</tt>, which defaults

 * to the {@link FutureTask} class provided in this package.  For example,

 * the implementation of <tt>submit(Runnable)</tt> creates an

 * associated <tt>RunnableFuture</tt> that is executed and

 * returned. Subclasses may override the <tt>newTaskFor</tt> methods

 * to return <tt>RunnableFuture</tt> implementations other than

 * <tt>FutureTask</tt>.

 *

 * <p> <b>Extension example</b>. Here is a sketch of a class

 * that customizes {@link ThreadPoolExecutor} to use

 * a <tt>CustomTask</tt> class instead of the default <tt>FutureTask</tt>:

 * <pre>

 * 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 <tt>RunnableFuture</tt> for the given runnable and default

     * value.

     *

     * @param runnable the runnable task being wrapped

     * @param value the default value for the returned future

     * @return a <tt>RunnableFuture</tt> which when run will run the

     * underlying runnable and which, as a <tt>Future</tt>, 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 <tt>RunnableFuture</tt> for the given callable task.

     *

     * @param callable the callable task being wrapped

     * @return a <tt>RunnableFuture</tt> which when run will call the

     * underlying callable and which, as a <tt>Future</tt>, 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);

    }

    public Future<?> submit(Runnable task) {

        if (task == null) throw new NullPointerException();

        RunnableFuture<Object> ftask = newTaskFor(task, null);

        execute(ftask);

        return ftask;

    }

    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;

    }

    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();

        List<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;

            long lastTime = (timed)? System.nanoTime() : 0;

            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();

                        long now = System.nanoTime();

                        nanos -= now - lastTime;

                        lastTime = now;

                    }

                    else

                        f = ecs.take();

                }

                if (f != null) {

                    --active;

                    try {

                        return f.get();

                    } catch (InterruptedException ie) {

                        throw ie;

                    } catch (ExecutionException eex) {

                        ee = eex;

                    } catch (RuntimeException rex) {

                        ee = new ExecutionException(rex);

                    }

                }

            }

            if (ee == null)

                ee = new ExecutionException();

            throw ee;

        } finally {

            for (Future<T> f : futures)

                f.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();

        List<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 (Future<T> f : futures) {

                if (!f.isDone()) {

                    try {

                        f.get();

                    } catch (CancellationException ignore) {

                    } catch (ExecutionException ignore) {

                    }

                }

            }

            done = true;

            return futures;

        } finally {

            if (!done)

                for (Future<T> f : futures)

                    f.cancel(true);

        }

    }

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

                                         long timeout, TimeUnit unit)

        throws InterruptedException {

        if (tasks == null || unit == null)

            throw new NullPointerException();

        long nanos = unit.toNanos(timeout);

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

        boolean done = false;

        try {

            for (Callable<T> t : tasks)

                futures.add(newTaskFor(t));

            long lastTime = System.nanoTime();

            // Interleave time checks and calls to execute in case

            // executor doesn't have any/much parallelism.

            Iterator<Future<T>> it = futures.iterator();

            while (it.hasNext()) {

                execute((Runnable)(it.next()));

                long now = System.nanoTime();

                nanos -= now - lastTime;

                lastTime = now;

                if (nanos <= 0)

                    return futures;

            }

            for (Future<T> f : futures) {

                if (!f.isDone()) {

                    if (nanos <= 0)

                        return futures;

                    try {

                        f.get(nanos, TimeUnit.NANOSECONDS);

                    } catch (CancellationException ignore) {

                    } catch (ExecutionException ignore) {

                    } catch (TimeoutException toe) {

                        return futures;

                    }

                    long now = System.nanoTime();

                    nanos -= now - lastTime;

                    lastTime = now;

                }

            }

            done = true;

            return futures;

        } finally {

            if (!done)

                for (Future<T> f : futures)

                    f.cancel(true);

        }

    }

}