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 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 │
       └──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

CONFORMING TO
       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                                                                          2021-03-22                                                                    SEM_POST(3)