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 sig-
       nal 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 4.16 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)