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

    This routine destroys the specified mutex by uninitializing it,
    and should be called when a mutex object is no longer referenced.
    After this routine is called, the Threads Library may reclaim
    internal storage used by the specified mutex.

    It is safe to destroy an initialized mutex that is unlocked.
    However, it is illegal to destroy a locked mutex.

    The results of this routine are unpredictable if the mutex object
    specified in the mutex argument does not currently exist, or is
    not initialized.