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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/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}.
 *
 * 

Extension example. Here is a sketch of a class * that customizes {@link ThreadPoolExecutor} to use * a {@code CustomTask} class instead of the default {@code FutureTask}: *

 {@code
 * public class CustomThreadPoolExecutor extends ThreadPoolExecutor {
 *
 *   static class CustomTask implements RunnableFuture {...}
 *
 *   protected  RunnableFuture newTaskFor(Callable c) {
 *       return new CustomTask(c);
 *   }
 *   protected  RunnableFuture newTaskFor(Runnable r, V v) {
 *       return new CustomTask(r, v);
 *   }
 *   // ... add constructors, etc.
 * }}
* * @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 * @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 RunnableFuture newTaskFor(Runnable runnable, T value) { return new FutureTask(runnable, value); } /** * Returns a {@code RunnableFuture} for the given callable task. * * @param callable the callable task being wrapped * @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 RunnableFuture newTaskFor(Callable callable) { return new FutureTask(callable); } /** * @throws RejectedExecutionException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public Future submit(Runnable task) { if (task == null) throw new NullPointerException(); RunnableFuture ftask = newTaskFor(task, null); execute(ftask); return ftask; } /** * @throws RejectedExecutionException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public Future submit(Runnable task, T result) { if (task == null) throw new NullPointerException(); RunnableFuture ftask = newTaskFor(task, result); execute(ftask); return ftask; } /** * @throws RejectedExecutionException {@inheritDoc} * @throws NullPointerException {@inheritDoc} */ public Future submit(Callable task) { if (task == null) throw new NullPointerException(); RunnableFuture ftask = newTaskFor(task); execute(ftask); return ftask; } /** * the main mechanics of invokeAny. */ private T doInvokeAny(Collection> 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> futures = new ArrayList>(ntasks); ExecutorCompletionService ecs = new ExecutorCompletionService(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> it = tasks.iterator(); // Start one task for sure; the rest incrementally futures.add(ecs.submit(it.next())); --ntasks; int active = 1; for (;;) { Future 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 invokeAny(Collection> tasks) throws InterruptedException, ExecutionException { try { return doInvokeAny(tasks, false, 0); } catch (TimeoutException cannotHappen) { assert false; return null; } } public T invokeAny(Collection> tasks, long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException { return doInvokeAny(tasks, true, unit.toNanos(timeout)); } public List> invokeAll(Collection> tasks) throws InterruptedException { if (tasks == null) throw new NullPointerException(); ArrayList> futures = new ArrayList>(tasks.size()); boolean done = false; try { for (Callable t : tasks) { RunnableFuture f = newTaskFor(t); futures.add(f); execute(f); } for (int i = 0, size = futures.size(); i < size; i++) { Future 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 List> invokeAll(Collection> tasks, long timeout, TimeUnit unit) throws InterruptedException { if (tasks == null) throw new NullPointerException(); long nanos = unit.toNanos(timeout); ArrayList> futures = new ArrayList>(tasks.size()); boolean done = false; try { for (Callable 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 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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