Use the sem_open function to establish the connection between a
    named semaphore and a process. Subsequently, the calling process
    can reference the semaphore by using the address returned from
    the call. The semaphore is available in subsequent calls to sem_
    wait, sem_trywait, sem_post, and sem_getvalue functions. The
    semaphore remains usable by the process until the semaphore is
    closed by a successful call to the sem_close function.

    The O_CREAT option bit in the ooption parameter controls whether
    the semaphore is created or only opened by the call to sem_open.

    A created semaphore's user ID is set to the user ID of the
    calling process and its group ID is set to a system default group
    or to the group ID of the process. The semaphore's permission
    bits are set to the value of the mode argument, except for those
    set in the file mode creation mask of the process.

    After a semaphore is created, other processes can open the
    semaphore by calling sem_open with the same value for the name
    argument.