//
  // 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,
  //      since, after all, this class is also a reentrant mutual exclusion lock!?