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sem_getvalue(3) — Linux manual page

sem_getvalue(3)          Library Functions Manualsem_getvalue(3)

NAME        top

       sem_getvalue - get the value of a semaphore

LIBRARY        top

       POSIX threads library (libpthread,-lpthread)

SYNOPSIS        top

#include <semaphore.h>int sem_getvalue(sem_t *restrictsem, int *restrictsval);

DESCRIPTION        top

sem_getvalue() places the current value of the semaphore pointed       tosem into the integer pointed to bysval.       If one or more processes or threads are blocked waiting to lock       the semaphore withsem_wait(3), POSIX.1 permits two possibilities       for the value returned insval: either 0 is returned; or a       negative number whose absolute value is the count of the number of       processes and threads currently blocked insem_wait(3).  Linux       adopts the former behavior.

RETURN VALUE        top

sem_getvalue() returns 0 on success; on error, -1 is returned anderrno is set to indicate the error.

ERRORS        top

EINVALsem is not a valid semaphore.  (The glibc implementation              currently does not check whethersem is valid.)

ATTRIBUTES        top

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

STANDARDS        top

       POSIX.1-2008.

HISTORY        top

       POSIX.1-2001.

NOTES        top

       The value of the semaphore may already have changed by the timesem_getvalue() returns.

SEE ALSO        top

sem_post(3),sem_wait(3),sem_overview(7)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       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-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-05-17sem_getvalue(3)

Pages that refer to this page:sem_close(3), sem_open(3), sem_post(3), sem_unlink(3), sem_wait(3), sem_overview(7)

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