001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.util.concurrent;
016
017import static com.google.common.base.Preconditions.checkArgument;
018import static com.google.common.base.Preconditions.checkNotNull;
019
020import com.google.common.annotations.Beta;
021import com.google.common.annotations.GwtCompatible;
022import com.google.common.annotations.GwtIncompatible;
023import com.google.common.annotations.VisibleForTesting;
024import com.google.common.base.Supplier;
025import com.google.common.base.Throwables;
026import com.google.common.collect.Lists;
027import com.google.common.collect.Queues;
028import com.google.common.util.concurrent.ForwardingListenableFuture.SimpleForwardingListenableFuture;
029import com.google.errorprone.annotations.CanIgnoreReturnValue;
030import java.lang.reflect.InvocationTargetException;
031import java.util.Collection;
032import java.util.Collections;
033import java.util.Iterator;
034import java.util.List;
035import java.util.concurrent.BlockingQueue;
036import java.util.concurrent.Callable;
037import java.util.concurrent.Delayed;
038import java.util.concurrent.ExecutionException;
039import java.util.concurrent.Executor;
040import java.util.concurrent.ExecutorService;
041import java.util.concurrent.Executors;
042import java.util.concurrent.Future;
043import java.util.concurrent.RejectedExecutionException;
044import java.util.concurrent.ScheduledExecutorService;
045import java.util.concurrent.ScheduledFuture;
046import java.util.concurrent.ScheduledThreadPoolExecutor;
047import java.util.concurrent.ThreadFactory;
048import java.util.concurrent.ThreadPoolExecutor;
049import java.util.concurrent.ThreadPoolExecutor.CallerRunsPolicy;
050import java.util.concurrent.TimeUnit;
051import java.util.concurrent.TimeoutException;
052import javax.annotation.concurrent.GuardedBy;
053
054/**
055 * Factory and utility methods for {@link java.util.concurrent.Executor}, {@link ExecutorService},
056 * and {@link ThreadFactory}.
057 *
058 * @author Eric Fellheimer
059 * @author Kyle Littlefield
060 * @author Justin Mahoney
061 * @since 3.0
062 */
063@GwtCompatible(emulated = true)
064public final class MoreExecutors {
065  private MoreExecutors() {}
066
067  /**
068   * Converts the given ThreadPoolExecutor into an ExecutorService that exits when the application
069   * is complete. It does so by using daemon threads and adding a shutdown hook to wait for their
070   * completion.
071   *
072   * <p>This is mainly for fixed thread pools. See {@link Executors#newFixedThreadPool(int)}.
073   *
074   * @param executor the executor to modify to make sure it exits when the application is finished
075   * @param terminationTimeout how long to wait for the executor to finish before terminating the
076   *     JVM
077   * @param timeUnit unit of time for the time parameter
078   * @return an unmodifiable version of the input which will not hang the JVM
079   */
080  @Beta
081  @GwtIncompatible // TODO
082  public static ExecutorService getExitingExecutorService(
083      ThreadPoolExecutor executor, long terminationTimeout, TimeUnit timeUnit) {
084    return new Application().getExitingExecutorService(executor, terminationTimeout, timeUnit);
085  }
086
087  /**
088   * Converts the given ScheduledThreadPoolExecutor into a ScheduledExecutorService that exits when
089   * the application is complete. It does so by using daemon threads and adding a shutdown hook to
090   * wait for their completion.
091   *
092   * <p>This is mainly for fixed thread pools. See {@link Executors#newScheduledThreadPool(int)}.
093   *
094   * @param executor the executor to modify to make sure it exits when the application is finished
095   * @param terminationTimeout how long to wait for the executor to finish before terminating the
096   *     JVM
097   * @param timeUnit unit of time for the time parameter
098   * @return an unmodifiable version of the input which will not hang the JVM
099   */
100  @Beta
101  @GwtIncompatible // TODO
102  public static ScheduledExecutorService getExitingScheduledExecutorService(
103      ScheduledThreadPoolExecutor executor, long terminationTimeout, TimeUnit timeUnit) {
104    return new Application()
105        .getExitingScheduledExecutorService(executor, terminationTimeout, timeUnit);
106  }
107
108  /**
109   * Add a shutdown hook to wait for thread completion in the given {@link ExecutorService service}.
110   * This is useful if the given service uses daemon threads, and we want to keep the JVM from
111   * exiting immediately on shutdown, instead giving these daemon threads a chance to terminate
112   * normally.
113   *
114   * @param service ExecutorService which uses daemon threads
115   * @param terminationTimeout how long to wait for the executor to finish before terminating the
116   *     JVM
117   * @param timeUnit unit of time for the time parameter
118   */
119  @Beta
120  @GwtIncompatible // TODO
121  public static void addDelayedShutdownHook(
122      ExecutorService service, long terminationTimeout, TimeUnit timeUnit) {
123    new Application().addDelayedShutdownHook(service, terminationTimeout, timeUnit);
124  }
125
126  /**
127   * Converts the given ThreadPoolExecutor into an ExecutorService that exits when the application
128   * is complete. It does so by using daemon threads and adding a shutdown hook to wait for their
129   * completion.
130   *
131   * <p>This method waits 120 seconds before continuing with JVM termination, even if the executor
132   * has not finished its work.
133   *
134   * <p>This is mainly for fixed thread pools. See {@link Executors#newFixedThreadPool(int)}.
135   *
136   * @param executor the executor to modify to make sure it exits when the application is finished
137   * @return an unmodifiable version of the input which will not hang the JVM
138   */
139  @Beta
140  @GwtIncompatible // concurrency
141  public static ExecutorService getExitingExecutorService(ThreadPoolExecutor executor) {
142    return new Application().getExitingExecutorService(executor);
143  }
144
145  /**
146   * Converts the given ScheduledThreadPoolExecutor into a ScheduledExecutorService that exits when
147   * the application is complete. It does so by using daemon threads and adding a shutdown hook to
148   * wait for their completion.
149   *
150   * <p>This method waits 120 seconds before continuing with JVM termination, even if the executor
151   * has not finished its work.
152   *
153   * <p>This is mainly for fixed thread pools. See {@link Executors#newScheduledThreadPool(int)}.
154   *
155   * @param executor the executor to modify to make sure it exits when the application is finished
156   * @return an unmodifiable version of the input which will not hang the JVM
157   */
158  @Beta
159  @GwtIncompatible // TODO
160  public static ScheduledExecutorService getExitingScheduledExecutorService(
161      ScheduledThreadPoolExecutor executor) {
162    return new Application().getExitingScheduledExecutorService(executor);
163  }
164
165  /** Represents the current application to register shutdown hooks. */
166  @GwtIncompatible // TODO
167  @VisibleForTesting
168  static class Application {
169
170    final ExecutorService getExitingExecutorService(
171        ThreadPoolExecutor executor, long terminationTimeout, TimeUnit timeUnit) {
172      useDaemonThreadFactory(executor);
173      ExecutorService service = Executors.unconfigurableExecutorService(executor);
174      addDelayedShutdownHook(executor, terminationTimeout, timeUnit);
175      return service;
176    }
177
178    final ScheduledExecutorService getExitingScheduledExecutorService(
179        ScheduledThreadPoolExecutor executor, long terminationTimeout, TimeUnit timeUnit) {
180      useDaemonThreadFactory(executor);
181      ScheduledExecutorService service = Executors.unconfigurableScheduledExecutorService(executor);
182      addDelayedShutdownHook(executor, terminationTimeout, timeUnit);
183      return service;
184    }
185
186    final void addDelayedShutdownHook(
187        final ExecutorService service, final long terminationTimeout, final TimeUnit timeUnit) {
188      checkNotNull(service);
189      checkNotNull(timeUnit);
190      addShutdownHook(
191          MoreExecutors.newThread(
192              "DelayedShutdownHook-for-" + service,
193              new Runnable() {
194                @Override
195                public void run() {
196                  try {
197                    // We'd like to log progress and failures that may arise in the
198                    // following code, but unfortunately the behavior of logging
199                    // is undefined in shutdown hooks.
200                    // This is because the logging code installs a shutdown hook of its
201                    // own. See Cleaner class inside {@link LogManager}.
202                    service.shutdown();
203                    service.awaitTermination(terminationTimeout, timeUnit);
204                  } catch (InterruptedException ignored) {
205                    // We're shutting down anyway, so just ignore.
206                  }
207                }
208              }));
209    }
210
211    final ExecutorService getExitingExecutorService(ThreadPoolExecutor executor) {
212      return getExitingExecutorService(executor, 120, TimeUnit.SECONDS);
213    }
214
215    final ScheduledExecutorService getExitingScheduledExecutorService(
216        ScheduledThreadPoolExecutor executor) {
217      return getExitingScheduledExecutorService(executor, 120, TimeUnit.SECONDS);
218    }
219
220    @VisibleForTesting
221    void addShutdownHook(Thread hook) {
222      Runtime.getRuntime().addShutdownHook(hook);
223    }
224  }
225
226  @GwtIncompatible // TODO
227  private static void useDaemonThreadFactory(ThreadPoolExecutor executor) {
228    executor.setThreadFactory(
229        new ThreadFactoryBuilder()
230            .setDaemon(true)
231            .setThreadFactory(executor.getThreadFactory())
232            .build());
233  }
234
235  // See newDirectExecutorService javadoc for behavioral notes.
236  @GwtIncompatible // TODO
237  private static final class DirectExecutorService extends AbstractListeningExecutorService {
238    /**
239     * Lock used whenever accessing the state variables (runningTasks, shutdown) of the executor
240     */
241    private final Object lock = new Object();
242
243    /*
244     * Conceptually, these two variables describe the executor being in
245     * one of three states:
246     *   - Active: shutdown == false
247     *   - Shutdown: runningTasks > 0 and shutdown == true
248     *   - Terminated: runningTasks == 0 and shutdown == true
249     */
250    @GuardedBy("lock")
251    private int runningTasks = 0;
252
253    @GuardedBy("lock")
254    private boolean shutdown = false;
255
256    @Override
257    public void execute(Runnable command) {
258      startTask();
259      try {
260        command.run();
261      } finally {
262        endTask();
263      }
264    }
265
266    @Override
267    public boolean isShutdown() {
268      synchronized (lock) {
269        return shutdown;
270      }
271    }
272
273    @Override
274    public void shutdown() {
275      synchronized (lock) {
276        shutdown = true;
277        if (runningTasks == 0) {
278          lock.notifyAll();
279        }
280      }
281    }
282
283    // See newDirectExecutorService javadoc for unusual behavior of this method.
284    @Override
285    public List<Runnable> shutdownNow() {
286      shutdown();
287      return Collections.emptyList();
288    }
289
290    @Override
291    public boolean isTerminated() {
292      synchronized (lock) {
293        return shutdown && runningTasks == 0;
294      }
295    }
296
297    @Override
298    public boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
299      long nanos = unit.toNanos(timeout);
300      synchronized (lock) {
301        while (true) {
302          if (shutdown && runningTasks == 0) {
303            return true;
304          } else if (nanos <= 0) {
305            return false;
306          } else {
307            long now = System.nanoTime();
308            TimeUnit.NANOSECONDS.timedWait(lock, nanos);
309            nanos -= System.nanoTime() - now; // subtract the actual time we waited
310          }
311        }
312      }
313    }
314
315    /**
316     * Checks if the executor has been shut down and increments the running task count.
317     *
318     * @throws RejectedExecutionException if the executor has been previously shutdown
319     */
320    private void startTask() {
321      synchronized (lock) {
322        if (shutdown) {
323          throw new RejectedExecutionException("Executor already shutdown");
324        }
325        runningTasks++;
326      }
327    }
328
329    /**
330     * Decrements the running task count.
331     */
332    private void endTask() {
333      synchronized (lock) {
334        int numRunning = --runningTasks;
335        if (numRunning == 0) {
336          lock.notifyAll();
337        }
338      }
339    }
340  }
341
342  /**
343   * Creates an executor service that runs each task in the thread that invokes
344   * {@code execute/submit}, as in {@link CallerRunsPolicy} This applies both to individually
345   * submitted tasks and to collections of tasks submitted via {@code invokeAll} or
346   * {@code invokeAny}. In the latter case, tasks will run serially on the calling thread. Tasks are
347   * run to completion before a {@code Future} is returned to the caller (unless the executor has
348   * been shutdown).
349   *
350   * <p>Although all tasks are immediately executed in the thread that submitted the task, this
351   * {@code ExecutorService} imposes a small locking overhead on each task submission in order to
352   * implement shutdown and termination behavior.
353   *
354   * <p>The implementation deviates from the {@code ExecutorService} specification with regards to
355   * the {@code shutdownNow} method. First, "best-effort" with regards to canceling running tasks is
356   * implemented as "no-effort". No interrupts or other attempts are made to stop threads executing
357   * tasks. Second, the returned list will always be empty, as any submitted task is considered to
358   * have started execution. This applies also to tasks given to {@code invokeAll} or
359   * {@code invokeAny} which are pending serial execution, even the subset of the tasks that have
360   * not yet started execution. It is unclear from the {@code ExecutorService} specification if
361   * these should be included, and it's much easier to implement the interpretation that they not
362   * be. Finally, a call to {@code shutdown} or {@code shutdownNow} may result in concurrent calls
363   * to {@code invokeAll/invokeAny} throwing RejectedExecutionException, although a subset of the
364   * tasks may already have been executed.
365   *
366   * @since 18.0 (present as MoreExecutors.sameThreadExecutor() since 10.0)
367   */
368  @GwtIncompatible // TODO
369  public static ListeningExecutorService newDirectExecutorService() {
370    return new DirectExecutorService();
371  }
372
373  /**
374   * Returns an {@link Executor} that runs each task in the thread that invokes
375   * {@link Executor#execute execute}, as in {@link CallerRunsPolicy}.
376   *
377   * <p>This instance is equivalent to: <pre>   {@code
378   *   final class DirectExecutor implements Executor {
379   *     public void execute(Runnable r) {
380   *       r.run();
381   *     }
382   *   }}</pre>
383   *
384   * <p>This should be preferred to {@link #newDirectExecutorService()} because implementing the
385   * {@link ExecutorService} subinterface necessitates significant performance overhead.
386   *
387   * @since 18.0
388   */
389  public static Executor directExecutor() {
390    return DirectExecutor.INSTANCE;
391  }
392
393  /** See {@link #directExecutor} for behavioral notes. */
394  private enum DirectExecutor implements Executor {
395    INSTANCE;
396
397    @Override
398    public void execute(Runnable command) {
399      command.run();
400    }
401
402    @Override
403    public String toString() {
404      return "MoreExecutors.directExecutor()";
405    }
406  }
407
408  /**
409   * Creates an {@link ExecutorService} whose {@code submit} and {@code
410   * invokeAll} methods submit {@link ListenableFutureTask} instances to the given delegate
411   * executor. Those methods, as well as {@code execute} and {@code invokeAny}, are implemented in
412   * terms of calls to {@code
413   * delegate.execute}. All other methods are forwarded unchanged to the delegate. This implies that
414   * the returned {@code ListeningExecutorService} never calls the delegate's {@code submit},
415   * {@code invokeAll}, and {@code
416   * invokeAny} methods, so any special handling of tasks must be implemented in the delegate's
417   * {@code execute} method or by wrapping the returned {@code
418   * ListeningExecutorService}.
419   *
420   * <p>If the delegate executor was already an instance of {@code
421   * ListeningExecutorService}, it is returned untouched, and the rest of this documentation does
422   * not apply.
423   *
424   * @since 10.0
425   */
426  @GwtIncompatible // TODO
427  public static ListeningExecutorService listeningDecorator(ExecutorService delegate) {
428    return (delegate instanceof ListeningExecutorService)
429        ? (ListeningExecutorService) delegate
430        : (delegate instanceof ScheduledExecutorService)
431            ? new ScheduledListeningDecorator((ScheduledExecutorService) delegate)
432            : new ListeningDecorator(delegate);
433  }
434
435  /**
436   * Creates a {@link ScheduledExecutorService} whose {@code submit} and {@code invokeAll} methods
437   * submit {@link ListenableFutureTask} instances to the given delegate executor. Those methods, as
438   * well as {@code execute} and {@code invokeAny}, are implemented in terms of calls to {@code
439   * delegate.execute}. All other methods are forwarded unchanged to the delegate. This implies that
440   * the returned {@code ListeningScheduledExecutorService} never calls the delegate's {@code
441   * submit}, {@code invokeAll}, and {@code invokeAny} methods, so any special handling of tasks
442   * must be implemented in the delegate's {@code execute} method or by wrapping the returned {@code
443   * ListeningScheduledExecutorService}.
444   *
445   * <p>If the delegate executor was already an instance of {@code
446   * ListeningScheduledExecutorService}, it is returned untouched, and the rest of this
447   * documentation does not apply.
448   *
449   * @since 10.0
450   */
451  @GwtIncompatible // TODO
452  public static ListeningScheduledExecutorService listeningDecorator(
453      ScheduledExecutorService delegate) {
454    return (delegate instanceof ListeningScheduledExecutorService)
455        ? (ListeningScheduledExecutorService) delegate
456        : new ScheduledListeningDecorator(delegate);
457  }
458
459  @GwtIncompatible // TODO
460  private static class ListeningDecorator extends AbstractListeningExecutorService {
461    private final ExecutorService delegate;
462
463    ListeningDecorator(ExecutorService delegate) {
464      this.delegate = checkNotNull(delegate);
465    }
466
467    @Override
468    public final boolean awaitTermination(long timeout, TimeUnit unit) throws InterruptedException {
469      return delegate.awaitTermination(timeout, unit);
470    }
471
472    @Override
473    public final boolean isShutdown() {
474      return delegate.isShutdown();
475    }
476
477    @Override
478    public final boolean isTerminated() {
479      return delegate.isTerminated();
480    }
481
482    @Override
483    public final void shutdown() {
484      delegate.shutdown();
485    }
486
487    @Override
488    public final List<Runnable> shutdownNow() {
489      return delegate.shutdownNow();
490    }
491
492    @Override
493    public final void execute(Runnable command) {
494      delegate.execute(command);
495    }
496  }
497
498  @GwtIncompatible // TODO
499  private static final class ScheduledListeningDecorator extends ListeningDecorator
500      implements ListeningScheduledExecutorService {
501    @SuppressWarnings("hiding")
502    final ScheduledExecutorService delegate;
503
504    ScheduledListeningDecorator(ScheduledExecutorService delegate) {
505      super(delegate);
506      this.delegate = checkNotNull(delegate);
507    }
508
509    @Override
510    public ListenableScheduledFuture<?> schedule(Runnable command, long delay, TimeUnit unit) {
511      TrustedListenableFutureTask<Void> task = TrustedListenableFutureTask.create(command, null);
512      ScheduledFuture<?> scheduled = delegate.schedule(task, delay, unit);
513      return new ListenableScheduledTask<Void>(task, scheduled);
514    }
515
516    @Override
517    public <V> ListenableScheduledFuture<V> schedule(
518        Callable<V> callable, long delay, TimeUnit unit) {
519      TrustedListenableFutureTask<V> task = TrustedListenableFutureTask.create(callable);
520      ScheduledFuture<?> scheduled = delegate.schedule(task, delay, unit);
521      return new ListenableScheduledTask<V>(task, scheduled);
522    }
523
524    @Override
525    public ListenableScheduledFuture<?> scheduleAtFixedRate(
526        Runnable command, long initialDelay, long period, TimeUnit unit) {
527      NeverSuccessfulListenableFutureTask task = new NeverSuccessfulListenableFutureTask(command);
528      ScheduledFuture<?> scheduled = delegate.scheduleAtFixedRate(task, initialDelay, period, unit);
529      return new ListenableScheduledTask<Void>(task, scheduled);
530    }
531
532    @Override
533    public ListenableScheduledFuture<?> scheduleWithFixedDelay(
534        Runnable command, long initialDelay, long delay, TimeUnit unit) {
535      NeverSuccessfulListenableFutureTask task = new NeverSuccessfulListenableFutureTask(command);
536      ScheduledFuture<?> scheduled =
537          delegate.scheduleWithFixedDelay(task, initialDelay, delay, unit);
538      return new ListenableScheduledTask<Void>(task, scheduled);
539    }
540
541    private static final class ListenableScheduledTask<V>
542        extends SimpleForwardingListenableFuture<V> implements ListenableScheduledFuture<V> {
543
544      private final ScheduledFuture<?> scheduledDelegate;
545
546      public ListenableScheduledTask(
547          ListenableFuture<V> listenableDelegate, ScheduledFuture<?> scheduledDelegate) {
548        super(listenableDelegate);
549        this.scheduledDelegate = scheduledDelegate;
550      }
551
552      @Override
553      public boolean cancel(boolean mayInterruptIfRunning) {
554        boolean cancelled = super.cancel(mayInterruptIfRunning);
555        if (cancelled) {
556          // Unless it is cancelled, the delegate may continue being scheduled
557          scheduledDelegate.cancel(mayInterruptIfRunning);
558
559          // TODO(user): Cancel "this" if "scheduledDelegate" is cancelled.
560        }
561        return cancelled;
562      }
563
564      @Override
565      public long getDelay(TimeUnit unit) {
566        return scheduledDelegate.getDelay(unit);
567      }
568
569      @Override
570      public int compareTo(Delayed other) {
571        return scheduledDelegate.compareTo(other);
572      }
573    }
574
575    @GwtIncompatible // TODO
576    private static final class NeverSuccessfulListenableFutureTask extends AbstractFuture<Void>
577        implements Runnable {
578      private final Runnable delegate;
579
580      public NeverSuccessfulListenableFutureTask(Runnable delegate) {
581        this.delegate = checkNotNull(delegate);
582      }
583
584      @Override
585      public void run() {
586        try {
587          delegate.run();
588        } catch (Throwable t) {
589          setException(t);
590          throw Throwables.propagate(t);
591        }
592      }
593    }
594  }
595
596  /*
597   * This following method is a modified version of one found in
598   * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/test/tck/AbstractExecutorServiceTest.java?revision=1.30
599   * which contained the following notice:
600   *
601   * Written by Doug Lea with assistance from members of JCP JSR-166 Expert Group and released to
602   * the public domain, as explained at http://creativecommons.org/publicdomain/zero/1.0/
603   *
604   * Other contributors include Andrew Wright, Jeffrey Hayes, Pat Fisher, Mike Judd.
605   */
606
607  /**
608   * An implementation of {@link ExecutorService#invokeAny} for {@link ListeningExecutorService}
609   * implementations.
610   */
611  @GwtIncompatible static <T> T invokeAnyImpl(
612      ListeningExecutorService executorService,
613      Collection<? extends Callable<T>> tasks,
614      boolean timed,
615      long timeout,
616      TimeUnit unit)
617      throws InterruptedException, ExecutionException, TimeoutException {
618    checkNotNull(executorService);
619    checkNotNull(unit);
620    int ntasks = tasks.size();
621    checkArgument(ntasks > 0);
622    List<Future<T>> futures = Lists.newArrayListWithCapacity(ntasks);
623    BlockingQueue<Future<T>> futureQueue = Queues.newLinkedBlockingQueue();
624    long timeoutNanos = unit.toNanos(timeout);
625
626    // For efficiency, especially in executors with limited
627    // parallelism, check to see if previously submitted tasks are
628    // done before submitting more of them. This interleaving
629    // plus the exception mechanics account for messiness of main
630    // loop.
631
632    try {
633      // Record exceptions so that if we fail to obtain any
634      // result, we can throw the last exception we got.
635      ExecutionException ee = null;
636      long lastTime = timed ? System.nanoTime() : 0;
637      Iterator<? extends Callable<T>> it = tasks.iterator();
638
639      futures.add(submitAndAddQueueListener(executorService, it.next(), futureQueue));
640      --ntasks;
641      int active = 1;
642
643      while (true) {
644        Future<T> f = futureQueue.poll();
645        if (f == null) {
646          if (ntasks > 0) {
647            --ntasks;
648            futures.add(submitAndAddQueueListener(executorService, it.next(), futureQueue));
649            ++active;
650          } else if (active == 0) {
651            break;
652          } else if (timed) {
653            f = futureQueue.poll(timeoutNanos, TimeUnit.NANOSECONDS);
654            if (f == null) {
655              throw new TimeoutException();
656            }
657            long now = System.nanoTime();
658            timeoutNanos -= now - lastTime;
659            lastTime = now;
660          } else {
661            f = futureQueue.take();
662          }
663        }
664        if (f != null) {
665          --active;
666          try {
667            return f.get();
668          } catch (ExecutionException eex) {
669            ee = eex;
670          } catch (RuntimeException rex) {
671            ee = new ExecutionException(rex);
672          }
673        }
674      }
675
676      if (ee == null) {
677        ee = new ExecutionException(null);
678      }
679      throw ee;
680    } finally {
681      for (Future<T> f : futures) {
682        f.cancel(true);
683      }
684    }
685  }
686
687  /**
688   * Submits the task and adds a listener that adds the future to {@code queue} when it completes.
689   */
690  @GwtIncompatible // TODO
691  private static <T> ListenableFuture<T> submitAndAddQueueListener(
692      ListeningExecutorService executorService,
693      Callable<T> task,
694      final BlockingQueue<Future<T>> queue) {
695    final ListenableFuture<T> future = executorService.submit(task);
696    future.addListener(
697        new Runnable() {
698          @Override
699          public void run() {
700            queue.add(future);
701          }
702        },
703        directExecutor());
704    return future;
705  }
706
707  /**
708   * Returns a default thread factory used to create new threads.
709   *
710   * <p>On AppEngine, returns {@code ThreadManager.currentRequestThreadFactory()}. Otherwise,
711   * returns {@link Executors#defaultThreadFactory()}.
712   *
713   * @since 14.0
714   */
715  @Beta
716  @GwtIncompatible // concurrency
717  public static ThreadFactory platformThreadFactory() {
718    if (!isAppEngine()) {
719      return Executors.defaultThreadFactory();
720    }
721    try {
722      return (ThreadFactory)
723          Class.forName("com.google.appengine.api.ThreadManager")
724              .getMethod("currentRequestThreadFactory")
725              .invoke(null);
726    } catch (IllegalAccessException e) {
727      throw new RuntimeException("Couldn't invoke ThreadManager.currentRequestThreadFactory", e);
728    } catch (ClassNotFoundException e) {
729      throw new RuntimeException("Couldn't invoke ThreadManager.currentRequestThreadFactory", e);
730    } catch (NoSuchMethodException e) {
731      throw new RuntimeException("Couldn't invoke ThreadManager.currentRequestThreadFactory", e);
732    } catch (InvocationTargetException e) {
733      throw Throwables.propagate(e.getCause());
734    }
735  }
736
737  @GwtIncompatible // TODO
738  private static boolean isAppEngine() {
739    if (System.getProperty("com.google.appengine.runtime.environment") == null) {
740      return false;
741    }
742    try {
743      // If the current environment is null, we're not inside AppEngine.
744      return Class.forName("com.google.apphosting.api.ApiProxy")
745              .getMethod("getCurrentEnvironment")
746              .invoke(null)
747          != null;
748    } catch (ClassNotFoundException e) {
749      // If ApiProxy doesn't exist, we're not on AppEngine at all.
750      return false;
751    } catch (InvocationTargetException e) {
752      // If ApiProxy throws an exception, we're not in a proper AppEngine environment.
753      return false;
754    } catch (IllegalAccessException e) {
755      // If the method isn't accessible, we're not on a supported version of AppEngine;
756      return false;
757    } catch (NoSuchMethodException e) {
758      // If the method doesn't exist, we're not on a supported version of AppEngine;
759      return false;
760    }
761  }
762
763  /**
764   * Creates a thread using {@link #platformThreadFactory}, and sets its name to {@code name} unless
765   * changing the name is forbidden by the security manager.
766   */
767  @GwtIncompatible // concurrency
768  static Thread newThread(String name, Runnable runnable) {
769    checkNotNull(name);
770    checkNotNull(runnable);
771    Thread result = platformThreadFactory().newThread(runnable);
772    try {
773      result.setName(name);
774    } catch (SecurityException e) {
775      // OK if we can't set the name in this environment.
776    }
777    return result;
778  }
779
780  // TODO(lukes): provide overloads for ListeningExecutorService? ListeningScheduledExecutorService?
781  // TODO(lukes): provide overloads that take constant strings? Function<Runnable, String>s to
782  // calculate names?
783
784  /**
785   * Creates an {@link Executor} that renames the {@link Thread threads} that its tasks run in.
786   *
787   * <p>The names are retrieved from the {@code nameSupplier} on the thread that is being renamed
788   * right before each task is run. The renaming is best effort, if a {@link SecurityManager}
789   * prevents the renaming then it will be skipped but the tasks will still execute.
790   *
791   *
792   * @param executor The executor to decorate
793   * @param nameSupplier The source of names for each task
794   */
795  @GwtIncompatible // concurrency
796  static Executor renamingDecorator(final Executor executor, final Supplier<String> nameSupplier) {
797    checkNotNull(executor);
798    checkNotNull(nameSupplier);
799    if (isAppEngine()) {
800      // AppEngine doesn't support thread renaming, so don't even try
801      return executor;
802    }
803    return new Executor() {
804      @Override
805      public void execute(Runnable command) {
806        executor.execute(Callables.threadRenaming(command, nameSupplier));
807      }
808    };
809  }
810
811  /**
812   * Creates an {@link ExecutorService} that renames the {@link Thread threads} that its tasks run
813   * in.
814   *
815   * <p>The names are retrieved from the {@code nameSupplier} on the thread that is being renamed
816   * right before each task is run. The renaming is best effort, if a {@link SecurityManager}
817   * prevents the renaming then it will be skipped but the tasks will still execute.
818   *
819   *
820   * @param service The executor to decorate
821   * @param nameSupplier The source of names for each task
822   */
823  @GwtIncompatible // concurrency
824  static ExecutorService renamingDecorator(
825      final ExecutorService service, final Supplier<String> nameSupplier) {
826    checkNotNull(service);
827    checkNotNull(nameSupplier);
828    if (isAppEngine()) {
829      // AppEngine doesn't support thread renaming, so don't even try.
830      return service;
831    }
832    return new WrappingExecutorService(service) {
833      @Override
834      protected <T> Callable<T> wrapTask(Callable<T> callable) {
835        return Callables.threadRenaming(callable, nameSupplier);
836      }
837
838      @Override
839      protected Runnable wrapTask(Runnable command) {
840        return Callables.threadRenaming(command, nameSupplier);
841      }
842    };
843  }
844
845  /**
846   * Creates a {@link ScheduledExecutorService} that renames the {@link Thread threads} that its
847   * tasks run in.
848   *
849   * <p>The names are retrieved from the {@code nameSupplier} on the thread that is being renamed
850   * right before each task is run. The renaming is best effort, if a {@link SecurityManager}
851   * prevents the renaming then it will be skipped but the tasks will still execute.
852   *
853   *
854   * @param service The executor to decorate
855   * @param nameSupplier The source of names for each task
856   */
857  @GwtIncompatible // concurrency
858  static ScheduledExecutorService renamingDecorator(
859      final ScheduledExecutorService service, final Supplier<String> nameSupplier) {
860    checkNotNull(service);
861    checkNotNull(nameSupplier);
862    if (isAppEngine()) {
863      // AppEngine doesn't support thread renaming, so don't even try.
864      return service;
865    }
866    return new WrappingScheduledExecutorService(service) {
867      @Override
868      protected <T> Callable<T> wrapTask(Callable<T> callable) {
869        return Callables.threadRenaming(callable, nameSupplier);
870      }
871
872      @Override
873      protected Runnable wrapTask(Runnable command) {
874        return Callables.threadRenaming(command, nameSupplier);
875      }
876    };
877  }
878
879  /**
880   * Shuts down the given executor service gradually, first disabling new submissions and later, if
881   * necessary, cancelling remaining tasks.
882   *
883   * <p>The method takes the following steps:
884   * <ol>
885   * <li>calls {@link ExecutorService#shutdown()}, disabling acceptance of new submitted tasks.
886   * <li>awaits executor service termination for half of the specified timeout.
887   * <li>if the timeout expires, it calls {@link ExecutorService#shutdownNow()}, cancelling pending
888   * tasks and interrupting running tasks.
889   * <li>awaits executor service termination for the other half of the specified timeout.
890   * </ol>
891   *
892   * <p>If, at any step of the process, the calling thread is interrupted, the method calls
893   * {@link ExecutorService#shutdownNow()} and returns.
894   *
895   * @param service the {@code ExecutorService} to shut down
896   * @param timeout the maximum time to wait for the {@code ExecutorService} to terminate
897   * @param unit the time unit of the timeout argument
898   * @return {@code true} if the {@code ExecutorService} was terminated successfully, {@code false}
899   *     if the call timed out or was interrupted
900   * @since 17.0
901   */
902  @Beta
903  @CanIgnoreReturnValue
904  @GwtIncompatible // concurrency
905  public static boolean shutdownAndAwaitTermination(
906      ExecutorService service, long timeout, TimeUnit unit) {
907    long halfTimeoutNanos = unit.toNanos(timeout) / 2;
908    // Disable new tasks from being submitted
909    service.shutdown();
910    try {
911      // Wait for half the duration of the timeout for existing tasks to terminate
912      if (!service.awaitTermination(halfTimeoutNanos, TimeUnit.NANOSECONDS)) {
913        // Cancel currently executing tasks
914        service.shutdownNow();
915        // Wait the other half of the timeout for tasks to respond to being cancelled
916        service.awaitTermination(halfTimeoutNanos, TimeUnit.NANOSECONDS);
917      }
918    } catch (InterruptedException ie) {
919      // Preserve interrupt status
920      Thread.currentThread().interrupt();
921      // (Re-)Cancel if current thread also interrupted
922      service.shutdownNow();
923    }
924    return service.isTerminated();
925  }
926
927  /**
928   * Returns an Executor that will propagate {@link RejectedExecutionException} from the delegate
929   * executor to the given {@code future}.
930   *
931   * <p>Note, the returned executor can only be used once.
932   */
933  static Executor rejectionPropagatingExecutor(
934      final Executor delegate, final AbstractFuture<?> future) {
935    checkNotNull(delegate);
936    checkNotNull(future);
937    if (delegate == directExecutor()) {
938      // directExecutor() cannot throw RejectedExecutionException
939      return delegate;
940    }
941    return new Executor() {
942      volatile boolean thrownFromDelegate = true;
943
944      @Override
945      public void execute(final Runnable command) {
946        try {
947          delegate.execute(
948              new Runnable() {
949                @Override
950                public void run() {
951                  thrownFromDelegate = false;
952                  command.run();
953                }
954              });
955        } catch (RejectedExecutionException e) {
956          if (thrownFromDelegate) {
957            // wrap exception?
958            future.setException(e);
959          }
960          // otherwise it must have been thrown from a transitive call and the delegate runnable
961          // should have handled it.
962        }
963      }
964    };
965  }
966}