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.

EXAMPLE

       See sem_wait(3).

SEE ALSO

       sem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7)

COLOPHON

       This page is part of release 4.15 of  the  Linux  man-pages  project.   A  description  of  the  project,
       information   about   reporting   bugs,   and   the  latest  version  of  this  page,  can  be  found  at
       https://www.kernel.org/doc/man-pages/.

Linux                                              2017-03-13                                        SEM_POST(3)