sem_post
Section: C Library Functions (3)
Updated: 2022-12-15
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NAME
sem_post - unlock a semaphore
LIBRARY
POSIX threads library
(libpthread, -lpthread)
SYNOPSIS
#include <semaphore.h>
int sem_post(sem_t *sem);
DESCRIPTION
sem_post()
increments (unlocks) the semaphore pointed to by
sem.
If the semaphore's value consequently becomes greater than zero,
then another process or thread blocked in a
sem_wait(3)
call will be woken up and proceed to lock the semaphore.
RETURN VALUE
sem_post()
returns 0 on success;
on error, the value of the semaphore is left unchanged,
-1 is returned, and
errno
is set to indicate the error.
ERRORS
- EINVAL
-
sem
is not a valid semaphore.
- EOVERFLOW
-
The maximum allowable value for a semaphore would be exceeded.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
sem_post()
| Thread safety | MT-Safe
|
STANDARDS
POSIX.1-2001.
NOTES
sem_post()
is async-signal-safe:
it may be safely called within a signal handler.
EXAMPLES
See
sem_wait(3)
and
shm_open(3).
SEE ALSO
sem_getvalue(3),
sem_wait(3),
sem_overview(7),
signal-safety(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- ATTRIBUTES
-
- STANDARDS
-
- NOTES
-
- EXAMPLES
-
- SEE ALSO
-
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