// (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

    for (Guard guard = activeGuards; guard != null; guard = guard.next) {
      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;

        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).

  private final Guard isStartable = new IsStartableGuard();

  @WeakOuter
  private final class IsStartableGuard extends Guard {
    IsStartableGuard() {
      super(AbstractService.this.monitor);
    }

    @Override
    public boolean isSatisfied() {
      return state() == NEW;
    }
  }

  private final Guard isStoppable = new IsStoppableGuard();

  @WeakOuter

   * found in any textbook.
   */

  /** Monitor guarding all access */
  final Monitor monitor;

  /** Guard for waiting takes */
  private final Monitor.Guard notEmpty;

  /** Guard for waiting puts */
  private final Monitor.Guard notFull;

  // Internal helper methods

  /** Circularly increment i. */
  final int inc(int i) {
    return (++i == items.length) ? 0 : i;
  }

   * found in any textbook.
   */

  /** Monitor guarding all access */
  final Monitor monitor;

  /** Guard for waiting takes */
  private final Monitor.Guard notEmpty;

  /** Guard for waiting puts */
  private final Monitor.Guard notFull;

  // Internal helper methods

  /** Circularly increment i. */
  final int inc(int i) {
    return (++i == items.length) ? 0 : i;
  }

  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();
        }
      };

  /**

     * which it is guaranteed that it can never become healthy.
     */
    final Monitor.Guard awaitHealthGuard = new AwaitHealthGuard();

    @WeakOuter
    final class AwaitHealthGuard extends Monitor.Guard {
      AwaitHealthGuard() {
        super(ServiceManagerState.this.monitor);
      }

      @Override

  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();
        }
      };

  /**

    std::list<Key>::iterator lra_iterator;
    /// The timestamp (seconds since epoch) at which the block was cached.
    uint64_t timestamp;
    /// Mutex to guard state variable
    absl::Mutex mu;
    /// The state of the block.
    FetchState state ABSL_GUARDED_BY(mu) = FetchState::CREATED;
    /// Wait on cond_var if state is FETCHING.
    absl::CondVar cond_var;
  };