boolean unused = hasNext();
            throw new AssertionError();
          }
        };
    assertThrows(IllegalStateException.class, iter::hasNext);
  }

  // Technically we should test other reentrant scenarios (9 combinations of
  // hasNext/next/peek), but we'll cop out for now, knowing that peek() and
  // next() both start by invoking hasNext() anyway.

 *
 * All event methods must execute fast, without external locking, cannot throw exceptions,
 * attempt to mutate the event parameters, or be reentrant back into the client.
 * Any IO - writing to files or network should be done asynchronously.
 */
internal abstract class ConnectionListener {
  /**
   * Invoked as soon as a call causes a connection to be started.
   */

          @Override
          protected Queue<Event> initialValue() {
            return new ArrayDeque<>();
          }
        };

    /** Per-thread dispatch state, used to avoid reentrant event dispatching. */
    @SuppressWarnings("ThreadLocalUsage") // Each Dispatcher needs its own state.
    private final ThreadLocal<Boolean> dispatching =
        new ThreadLocal<Boolean>() {
          @Override

  // TODO: Test waitFor(Guard, long, TimeUnit).
  // TODO: Test getQueueLength().
  // TODO: Test hasQueuedThreads().
  // TODO: Test getWaitQueueLength(Guard).
  // TODO: Test automatic signaling before leave, waitFor, and reentrant enterWhen.
  // TODO: Test blocking to re-enter monitor after being signaled.
  // TODO: Test interrupts with both interruptible and uninterruptible monitor.

       * class with a manual reference back to the "containing" class.)
       *
       * This has the nice-ish side effect of limiting reentrancy: run() calls
       * timeoutFuture.setException() calls run(). That reentrancy would already be harmless, since
       * timeoutFuture can be set (and delegate cancelled) only once. (And "set only once" is

 * using a lock, however it is dangerous to dispatch listeners while holding a lock because they
 * might run on the {@code directExecutor()} or be otherwise re-entrant (call back into your
 * object). So it is important to not call {@link #dispatch} while holding any locks. This is why
 * {@link #enqueue} and {@link #dispatch} are 2 different methods. It is expected that the decision