Description

   This routine initializes a mutex object with the Threads Library
   default mutex attributes. A mutex is a synchronization object
   that allows multiple threads to serialize their access to shared
   data.

   The mutex object is initialized and set to the unlocked state.

   Your program can use the PTHREAD_MUTEX_INITIALIZER macro to
   statically initialize a mutex object without calling this
   routine. Static initialization can be used only for a condition
   variable with storage class "extern" or "static" - "automatic"
   (stack local) objects must be initialized by calling tis_mutex_
   init(). Use this macro as follows:

      pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;