* @param unit a {@code TimeUnit} determining how to interpret the timeout parameter
   * @return the number of elements transferred
   * @throws InterruptedException if interrupted while waiting
   */
  @CanIgnoreReturnValue
  @J2ktIncompatible
  @GwtIncompatible // BlockingQueue
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  public static <E> int drain(

            // so when oldFuture completes it is safe to allow the next submitted task to
            // proceed. Doing this immediately here lets the next task run without waiting for
            // the cancelled task's executor to run the noop AsyncCallable.
            //
            // ---
            //

                   Why? At some point, presumably after
                   https://github.com/google/guava/commit/e06a8cec65815599e510d7f9c1ea9d2a8eaa438a,
                   builds with JDK8 began failing animal-sniffer with the error:

                   Failed to check signatures: Bad class file .../CollectionFuture$ListFuture.class

                   One way of dealing with that would be to disable

    } catch (NullPointerException expected) {
    }
    ImmutableList<String> result = builder.build();

    /*
     * Maybe it rejects all elements, or maybe it adds "a" before failing.
     * Either way is fine with us.
     */
    if (result.isEmpty()) {
      return;
    }
    assertTrue(ImmutableList.of("a").equals(result));
    assertEquals(1, result.size());
  }

    assertEquals("b", consumingIterator.next());
    assertThat(list).isEmpty();

    assertFalse(consumingIterator.hasNext());
  }

  @GwtIncompatible // ?
  // TODO: Figure out why this is failing in GWT.
  public void testConsumingIterable_duelingIterators() {
    // Test data
    List<String> list = Lists.newArrayList(asList("a", "b"));

    // Test & Verify

    assertEquals("b", consumingIterator.next());
    assertThat(list).isEmpty();

    assertFalse(consumingIterator.hasNext());
  }

  @GwtIncompatible // ?
  // TODO: Figure out why this is failing in GWT.
  public void testConsumingIterator_duelingIterators() {
    // Test data
    List<String> list = Lists.newArrayList("a", "b");

    // Test & Verify

  /**
   * Returns the result of calling {@link Future#get()} uninterruptibly on a task known not to throw
   * a checked exception. This makes {@code Future} more suitable for lightweight, fast-running
   * tasks that, barring bugs in the code, will not fail. This gives it exception-handling behavior
   * similar to that of {@code ForkJoinTask.join}.
   *
   * <p>Exceptions from {@code Future.get} are treated as follows:
   *
   * <ul>

    // being resumed. To avoid a flake in this scenario, calculate how long that thread actually
    // waited and assert based on that time. Empirically, the race where the thread ends up waiting
    // for 5.5 seconds happens about 2% of the time.
    boolean longWait = TimeUnit.NANOSECONDS.toSeconds(thread.timeSpentBlocked) >= 5;

      monitor.enter();
      try {
        if (!monitor.waitForUninterruptibly(awaitHealthGuard, timeout, unit)) {
          throw new TimeoutException(
              "Timeout waiting for the services to become healthy. The "
                  + "following services have not started: "
                  + Multimaps.filterKeys(servicesByState, in(ImmutableSet.of(NEW, STARTING))));
        }

  final long expireAfterWriteNanos;

  /** How long after the last write an entry becomes a candidate for refresh. */
  final long refreshNanos;

  /** Entries waiting to be consumed by the removal listener. */
  // TODO(fry): define a new type which creates event objects and automates the clear logic
  final Queue<RemovalNotification<K, V>> removalNotificationQueue;

  /**