sem_post(3) — Linux manual page

sem_post(3)             Library Functions Manual             sem_post(3)

NAME

       sem_post - unlock a semaphore

LIBRARY

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS

       #include <semaphore.h>

       int sem_post(sem_t *sem);

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 │
       └─────────────────────────────────────┴───────────────┴─────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       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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Linux man-pages 6.9.1          2024-05-02                    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)

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