NAME    [Toc]    [Back]

     sem_post - increment (unlock) a semaphore

SYNOPSIS    [Toc]    [Back]

     #include <semaphore.h>

     int
     sem_post(sem_t *sem);

DESCRIPTION    [Toc]    [Back]

     The 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().

     sem_post() is signal-reentrant and may be called within signal handlers.

RETURN VALUES    [Toc]    [Back]

     The  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.

ERRORS    [Toc]    [Back]

     sem_post() will fail if:

     [EINVAL]      sem points to an invalid semaphore.

SEE ALSO    [Toc]    [Back]

     sem_trywait(3), sem_wait(3)

STANDARDS    [Toc]    [Back]

     sem_post() conforms to ISO/IEC 9945-1:1996 (``POSIX'').

OpenBSD      3.6                        February     15,     2000