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SEM_POST(3)            FreeBSD Library Functions Manual            SEM_POST(3)

NAME
     sem_post - increment (unlock) a semaphore

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <semaphore.h>

     int
     sem_post(sem_t *sem);

DESCRIPTION
     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().

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

RETURN VALUES
     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
     The sem_post() function will fail if:

     [EINVAL]           The sem argument points to an invalid semaphore.

     [EOVERFLOW]        The semaphore value would exceed SEM_VALUE_MAX.

SEE ALSO
     sem_getvalue(3), sem_trywait(3), sem_wait(3)

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

FreeBSD 11.1-RELEASE-p4        January 28, 2015        FreeBSD 11.1-RELEASE-p4
Command Section