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)

COLOPHON

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