//
  // 3. I think "enterWhen(notEmpty)" reads better than "notEmpty.enter()".
  //
  // TODO(user): Implement ReentrantLock features:
  //    - toString() method
  //    - getOwner() method
  //    - getQueuedThreads() method
  //    - getWaitingThreads(Guard) method
  //    - implement Serializable
  //    - redo the API to be as close to identical to ReentrantLock as possible,