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.