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.