Description

   The sem_wait function locks the semaphore referenced by sem by
   performing a semaphore lock operation on it. If the semaphore
   value is zero, the sem_wait function blocks until it either locks
   the semaphore or is interrupted by a signal.

   The sem_wait and sem_trywait functions help ensure that the
   resource associated with the semaphore cannot be accessed by
   other processes. The semaphore remains locked until the process
   unlocks it with a call to the sem_post function.

   Use the sem_wait function instead of the sem_trywait function if
   the process should wait for access to the semaphore.