Monitor monitor = this.monitor;
    if (monitor.enterWhen(notEmpty, timeout, unit)) {
      try {
        return extract();
      } finally {
        monitor.leave();
      }
    } else {
      return null;
    }
  }

  @CanIgnoreReturnValue
  @Override
  public E take() throws InterruptedException {
    Monitor monitor = this.monitor;
    monitor.enterWhen(notEmpty);
    try {
      return extract();

  }

  @CanIgnoreReturnValue // pushed down from class to method
  @Override
  public @Nullable E poll(long timeout, TimeUnit unit) throws InterruptedException {
    Monitor monitor = this.monitor;
    if (monitor.enterWhen(notEmpty, timeout, unit)) {
      try {
        return q.poll();
      } finally {
        monitor.leave();
      }
    } else {
      return null;
    }
  }

 *
 *   public V get() throws InterruptedException {
 *     monitor.enterWhen(valuePresent);
 *     try {
 *       V result = value;
 *       value = null;
 *       return result;
 *     } finally {
 *       monitor.leave();
 *     }
 *   }
 *
 *   public void set(V newValue) throws InterruptedException {
 *     monitor.enterWhen(valueAbsent);
 *     try {
 *       value = newValue;
 *     } finally {