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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 14.0-RELEASE-p6 January 28, 2015 FreeBSD 14.0-RELEASE-p6