The Mutex package provides a way to synchronize access to user-defined
  objects. It consists of a single class, Mutex, that manages the
  creation, locking and unlocking of Mutex objects.

  Construction of a Mutex object creates a recursive mutex that
  users can lock and unlock using the appropriate member functions or
  parameterized manipulators. A recursive mutex is a mutex that can be
  locked many times by the same thread without causing the thread to enter
  a deadlock state. To completely unlock this kind of mutex, the thread
  must unlock the mutex the same number of times that the thread locked the
  mutex.

  Note that user-defined objects are not automatically thread safe. Users
  must supply synchronization for such objects if they are shared between
  threads.

  Header:

         #include <mutex.hxx>