Description

   The sem_trywait function locks a semaphore only if the semaphore
   is currently not locked. If the semaphore value is zero, the sem_
   trywait function returns without locking the semaphore.

   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.