NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON 

SEM_POST(3)               Linux Programmer's Manual              SEM_POST(3)

NAME         top

       sem_post - unlock a semaphore

SYNOPSIS         top

       #include <semaphore.h>
       int sem_post(sem_t *sem);
       Link with -pthread.

DESCRIPTION         top

       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         top

       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         top

       EINVAL sem is not a valid semaphore.
       EOVERFLOW
              The maximum allowable value for a semaphore would be exceeded.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌───────────┬───────────────┬─────────┐
       │Interface  │ Attribute     │ Value   │
       ├───────────┼───────────────┼─────────┤
       │sem_post() │ Thread safety │ MT-Safe │
       └───────────┴───────────────┴─────────┘

CONFORMING TO         top

       POSIX.1-2001.

NOTES         top

       sem_post() is async-signal-safe: it may be safely called within a
       signal handler.

EXAMPLE         top

       See sem_wait(3).

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 4.12 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)

Pages that refer to this page: sem_close(3),  sem_destroy(3),  sem_getvalue(3),  sem_init(3),  sem_open(3),  sem_timedwait(3p),  sem_unlink(3),  sem_wait(3),  sem_overview(7),  signal-safety(7)