sem_post(3) Library Functions Manual sem_post(3)
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.1-2008.
HISTORY
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)
Linux man-pages 6.9.1 2024-05-02 sem_post(3)
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