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