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

    This routine attempts to lock the specified mutex mutex. When
    this routine is called, an attempt is made immediately to lock
    the mutex. If the mutex is successfully locked, zero (0) is
    returned.

    If the specified mutex is already locked when this routine
    is called, the caller does not wait for the mutex to become
    available. [EBUSY] is returned, and the thread does not wait
    to acquire the lock.