sem                Successful completion. The function opens
                       the semaphore and returns the semaphore's
                       descriptor.
    sem_failed         Indicates an error. The function sets errno to
                       one of the following values:

                       o  EACCES-The named semaphore exists and
                          the permissions specified by ooption are
                          denied, or the named semaphore does not
                          exist and the permissions specified by
                          ooption are denied.

                       o  EEXIST-O_CREAT and O_EXCL are set, and the
                          named semaphore already exists.

                       o  EINVAL-The sem_open operation is not
                          supported for the given name. Or, O_CREAT
                          was specified in ooption and value was
                          greater than {SEM_VALUE_MAX}.

                       o  EMFILE-Too many semaphore descriptors or
                          file descriptors are currently in use by
                          this process.

                       o  ENAMETOOLONG-The length of the name string
                          exceeds {PATH_MAX}, or a pathname component
                          is longer than {NAME_MAX} while {_POSIX_NO_
                          TRUNC} is in effect.

                       o  ENFILE-Too many semaphores are currently
                          open in the system. ENOENT O_CREAT is
                          not set, and the named semaphore does not
                          exist.

                       o  ENOSPC-Insufficient space exists for the
                          creation of a new named semaphore.

                       o  EVMSERR-OpenVMS specific nontranslatable
                          error code.