0                  Successful completion. The sem_post function
                       performs a semaphore unlock operation,
                       unblocking a process.
    -1                 Indicates an error. The function sets errno to
                       one of the following values:

                       o  EINVAL - The sem argument is not a valid
                          semaphore.

                       o  EVMSERR - OpenVMS specific nontranslatable
                          error code.