Description

   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.