SEM_POST(3) Linux Programmer's Manual SEM_POST(3)
NAME
sem_post - unlock a semaphore
SYNOPSIS
#include <semaphore.h>
int sem_post(sem_t *sem);
Link with -pthread.
DESCRIPTION
sem_post() increments (unlocks) the semaphore pointed to by sem. If
the semaphore's value consequently becomes greater than zero, then an-
other 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 er-
ror.
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 at-
tributes(7).
┌───────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├───────────┼───────────────┼─────────┤
│sem_post() │ Thread safety │ MT-Safe │
└───────────┴───────────────┴─────────┘
CONFORMING TO
POSIX.1-2001.
NOTES
sem_post() is async-signal-safe: it may be safely called within a sig-
nal handler.
EXAMPLES
See sem_wait(3) and shm_open(3).
SEE ALSO
sem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7)
COLOPHON
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latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2020-08-13 SEM_POST(3)
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