sem_get() returns an id that can be used to
access the System V semaphore with the given key.
A second call to sem_get() for the same key will return a different semaphore identifier, but both identifiers access the same underlying semaphore.
key
max_acquire
The number of processes that can acquire the semaphore simultaneously
is set to max_acquire (defaults to 1).
permThe semaphore permissions. Defaults to 0666. Actually this value is set only if the process finds it is the only process currently attached to the semaphore.
auto_releaseSpecifies if the semaphore should be automatically released on request shutdown.