Class Data

include/process/rwlock.hpp:160–185

  };

  struct Data
  {
    Data() : read_locked(0), write_locked(false) {}

    ~Data()
    {
      // TODO(zhitao): Fail promises?
    }

    // The state of the lock can be either:
    //   (1) Unlocked: an incoming read or write grabs the lock.
    //
    //   (2) Read locked (by one or more readers): an incoming write
    //       will queue in the waiters. An incoming read will proceed
    //       if no one is waiting, otherwise it will queue.
    //
    //   (3) Write locked: incoming reads and writes will queue.

    size_t read_locked;
    bool write_locked;
    std::queue<Waiter> waiters;

    // Rather than use a process to serialize access to the
    // internal data we use a 'std::atomic_flag'.
    std::atomic_flag lock = ATOMIC_FLAG_INIT;
  };

  std::shared_ptr<Data> data;
};