0                  Successful completion. The function executes
                       the semaphore lock operation.
    -1                 Indicates an error. The function sets errno to
                       one of the following values:

                       o  EAGAIN - The semaphore was already locked
                          and cannot be locked by the sem_trywait
                          operation.

                       o  EINVAL - The sem argument does not refer to
                          a valid semaphore.

                       o  EVMSERR - OpenVMS specific nontranslatable
                          error code.