| SEM_POST(3) | Library Functions Manual | SEM_POST(3) | 
sem_post —
#include <semaphore.h>
int
  
  sem_post(sem_t
    *sem);
sem_post() function increments (unlocks) the
  semaphore pointed to by sem. If there are threads
  blocked on the semaphore when sem_post() is called,
  then the highest priority thread that has been blocked the longest on the
  semaphore will be allowed to return from sem_wait() or
  sem_timedwait().
sem_post() is signal-reentrant and may be
    called within signal handlers.
sem_post() function returns the value 0 if
  successful; otherwise the value -1 is returned and the global variable
  errno is set to indicate the error.
sem_post() will fail if:
EINVAL]sem_post() conforms to ISO/IEC
  9945-1:1996 (“POSIX.1”).
| February 29, 2012 | NetBSD 9.3 |