* strategies.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses Atomic FieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AggregateFutureState} (and all of
 * {@code com.google.common.util.concurrent}) in degenerate class loaders which make certain

    // ThreadLocal is not available to GWT, so we always reuse the same
    // instance.  It is always safe to return the same instance because
    // javascript is single-threaded, and only used by blocks that doesn't
    // involve async callbacks.
    return CHAR_BUFFER;
  }

  private Platform() {}

  protected abstract <V> ListenableFuture<V> createListenableFuture(
      V value, @Nullable Exception except, CountDownLatch waitOn);

  /** Tests that the {@link Future#get()} method blocks until a value is available. */
  public void testGetBlocksUntilValueAvailable() throws Throwable {

    assertFalse(future.isDone());
    assertFalse(future.isCancelled());

      /*
       * Using weak references here could let us release exceptions earlier, but:
       *
       * 1. On Android, querying a WeakReference blocks if the GC is doing an otherwise-concurrent
       * pass.
       *
       * 2. We would probably choose to compare exceptions using == instead of equals() (for

 * future.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses AtomicReferenceFieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AbstractFuture} (and all of {@code
 * com.google.common.util.concurrent}) in degenerate class loaders which make certain platform

  protected abstract <V> ListenableFuture<V> createListenableFuture(
      V value, @Nullable Exception except, CountDownLatch waitOn);

  /** Tests that the {@link Future#get()} method blocks until a value is available. */
  public void testGetBlocksUntilValueAvailable() throws Throwable {

    assertFalse(future.isDone());
    assertFalse(future.isCancelled());

 * strategies.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses Atomic FieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AggregateFutureState} (and all of
 * {@code com.google.common.util.concurrent}) in degenerate class loaders which make certain

    lockAndUnlockNested(detectingLocks, reps);
  }

  private static void lockAndUnlockNested(Lock[] locks, int reps) {
    for (int i = 0; i < reps; i++) {
      for (int j = 0; j < locks.length; j++) {
        locks[j].lock();
      }
      for (int j = locks.length - 1; j >= 0; j--) {
        locks[j].unlock();
      }
    }
  }

 * future.
 *
 * <ul>
 *   <li>SafeAtomicHelper: uses AtomicReferenceFieldsUpdaters to implement synchronization
 *   <li>SynchronizedHelper: uses {@code synchronized} blocks for synchronization
 * </ul>
 *
 * To force selection of our fallback strategies we load {@link AbstractFuture} (and all of {@code
 * com.google.common.util.concurrent}) in degenerate class loaders which make certain platform

   * then:
   *
   * <ul>
   *   <li>{@code isDone()} must return {@code true}
   *   <li>{@code isCancelled()} must return {@code false}
   *   <li>{@code get()} must not block, and it must throw an {@code ExecutionException} with the
   *       return value of this method as its cause
   * </ul>
   */
  public static
      Throwable tryInternalFastPathGetFailure(InternalFutureFailureAccess future) {