}

    /** Performs a GAS operation on the {@link #waiters} field. */
    @Override
    Waiter gasWaiters(AbstractFuture<?> future, Waiter update) {
      while (true) {
        Waiter waiter = future.waiters;
        if (update == waiter) {
          return waiter;
        }
        if (casWaiters(future, waiter, update)) {
          return waiter;
        }
      }
    }

    checkNotNull(conditionLikeObject);
    // TODO: Restore the following line when Monitor.hasWaiters() no longer acquires the lock.
    // assertEquals(false, invokeMethod("hasWaiters", conditionLikeObject));
    sendRequest(methodName, conditionLikeObject);
    Thread.sleep(DUE_DILIGENCE_MILLIS);
    assertEquals(true, invokeMethod("hasWaiters", conditionLikeObject));
    assertNull(responseQueue.poll());
  }

  /**

    checkNotNull(conditionLikeObject);
    // TODO: Restore the following line when Monitor.hasWaiters() no longer acquires the lock.
    // assertEquals(false, invokeMethod("hasWaiters", conditionLikeObject));
    sendRequest(methodName, conditionLikeObject);
    Thread.sleep(DUE_DILIGENCE_MILLIS);
    assertEquals(true, invokeMethod("hasWaiters", conditionLikeObject));
    assertNull(responseQueue.poll());
  }

  /**

    Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);
    assertThrows(IllegalMonitorStateException.class, () -> monitor1.hasWaiters(guard));
  }

  public void testNullMonitorInGuardConstructorThrowsNPE() {
    assertThrows(NullPointerException.class, () -> new FlagGuard(null));
  }

  public void testIsFair() {

    Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);
    assertThrows(IllegalMonitorStateException.class, () -> monitor1.hasWaiters(guard));
  }

  public void testNullMonitorInGuardConstructorThrowsNPE() {
    assertThrows(NullPointerException.class, () -> new FlagGuard(null));
  }

  public void testIsFair() {

   * and leaves, calling signalNextWaiter. With traditional locks and conditions, all the conditions
   * need to be signalled because it is not known which if any of them have waiters (and hasWaiters
   * can't be used reliably because of a check-then-act race). With our Monitor guards, we only
   * signal the first active guard that is satisfied. But the corresponding thread may have already