VMS Help POSIX Threads, PTHREAD routines, pthread_mutex_setname_np, Description  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    This routine changes the object name in the mutex object
    specified by the mutex argument to the value specified by the
    name argument. To set a new mutex object's object name, call this
    routine immediately after initializing the mutex object.

    The object name is a C language string and provides an identifier
    that is meaningful to a person debugging a multithreaded
    application. The maximum number of characters in the object name
    is 31.