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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)