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.
The number of processes that can acquire the semaphore simultaneously is set to max_acquire (defaults to 1).
The 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.
Specifies if the semaphore should be automatically released on request shutdown.