0                  Successful completion.
    -1                 Indicates an error. The function sets errno
                       to one of the following values, without
                       destroying the semaphore indicated by the
                       sem argument:

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

                       o  ENOSYS - The function is not implemented.

                       o  EVMSERR - OpenVMS specific nontranslatable
                          error code.

                       o  EBUSY - The processes are blocked on the
                          semaphore.