NAME
sem_post - unlock a semaphore
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#include <semaphore.h>int sem_post(sem_t *\nsem\n);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)