private static final long serialVersionUID = 5595510919245408276L;

  final PriorityQueue<E> q;
  final Monitor monitor = new Monitor(true);
  private final Monitor.Guard notEmpty =
      new Monitor.Guard(monitor) {
        @Override
        public boolean isSatisfied() {
          return !q.isEmpty();
        }
      };

  /**

      guard.condition.signalAll();
    }
  }

  /** Records that the current thread is about to wait on the specified guard. */
  @GuardedBy("lock")
  private void beginWaitingFor(Guard guard) {
    int waiters = guard.waiterCount++;
    if (waiters == 0) {
      // push guard onto activeGuards
      guard.next = activeGuards;
      activeGuards = guard;

  public final void testEnterWhen_initiallyTrue() throws Exception {
    TestGuard guard = new TestGuard(true);
    thread1.callAndAssertReturns(enterWhen(), guard);
  }

  public final void testEnterWhen_initiallyFalse() throws Exception {
    TestGuard guard = new TestGuard(false);
    thread1.callAndAssertWaits(enterWhen(), guard);
    monitor.enter();
    guard.setSatisfied(true);
    monitor.leave();

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

  public void testHasWaitersWithWrongMonitorThrowsIMSE() {
    Monitor monitor1 = new Monitor();
    Monitor monitor2 = new Monitor();
    FlagGuard guard = new FlagGuard(monitor2);

they arrived, with a great crowd assembled about them--all sorts
of little birds and beasts, as well as the whole pack of cards:
the Knave was standing before them, in chains, with a soldier on
each side to guard him; and near the King was the White Rabbit,
with a trumpet in one hand, and a scroll of parchment in the
other.  In the very middle of the court was a table, with a large

    // (b) Waiting for the single guard to become satisfied.
    // (c) Occupying the monitor and awaiting the tearDownLatch.
    //
    // Except for (c), every thread should occupy the monitor very briefly, and every thread leaves
    // the monitor with the guard satisfied. Therefore as soon as tearDownLatch is triggered, we
    // should be able to enter the monitor, and then we set the guard to satisfied for the benefit

        queue[0] = x;
        return 0;
      }
      int parentIndex = getParentIndex(index);
      E parentElement = elementData(parentIndex);
      if (parentIndex != 0) {
        /*
         * This is a guard for the case of the childless aunt node. Since the end of the array is
         * actually the middle of the heap, a smaller childless aunt node can become a child of x

    TestGuard guard = new TestGuard(true);
    thread1.callAndAssertReturns(true, enterIf(), guard);
    thread2.callAndAssertBlocks(enter());
  }

  public final void testEnterIf_initiallyFalse() throws Exception {
    TestGuard guard = new TestGuard(false);
    thread1.callAndAssertReturns(false, enterIf(), guard);
    thread2.callAndAssertReturns(enter());
  }

    if (obj instanceof Subscriber) {
      Subscriber that = (Subscriber) obj;
      // Use == so that different equal instances will still receive events.
      // We only guard against the case that the same object is registered
      // multiple times
      return target == that.target && method.equals(that.method);
    }
    return false;
  }

  /**

        Monitor monitor2 = new Monitor(fair2);
        FlagGuard guard = new FlagGuard(monitor2);
        Object[] arguments =
            (timed ? new Object[] {guard, 0L, TimeUnit.MILLISECONDS} : new Object[] {guard});
        boolean occupyMonitor = isWaitFor(method);
        if (occupyMonitor) {
          // If we don't already occupy the monitor, we'll get an IMSE regardless of the guard (see
          // generateWaitForWhenNotOccupyingTestCase).