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sem_post(3) — Linux manual page

sem_post(3) Library Functions Manual sem_post(3)

NAME top

 sem_post - unlock a semaphore

LIBRARY top

 POSIX threads library (libpthread, -lpthread)

SYNOPSIS top

 #include <semaphore.h>
 int sem_post(sem_t *sem);

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

STANDARDS top

 POSIX.1-2008.

HISTORY top

 POSIX.1-2001.

NOTES top

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

EXAMPLES top

 See sem_wait(3) and shm_open(3).

SEE ALSO top

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

COLOPHON top

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 user-space interface documentation) project. Information about
 the project can be found at 
 ⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
 for this manual page, see
 ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
 This page was obtained from the tarball man-pages-6.10.tar.gz
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 2025年02月02日. If you discover any rendering problems in this HTML
 version of the page, or you believe there is a better or more up-
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 man-pages@man7.org
Linux man-pages 6.10 2024年07月23日 sem_post(3)

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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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