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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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sem_getvalue(3) Library Functions Manual sem_getvalue(3)
sem_getvalue - get the value of a semaphore
POSIX threads library (libpthread, -lpthread)
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
sem_getvalue() places the current value of the semaphore pointed
to sem into the integer pointed to by sval.
If one or more processes or threads are blocked waiting to lock
the semaphore with sem_wait(3), POSIX.1 permits two possibilities
for the value returned in sval: either 0 is returned; or a
negative number whose absolute value is the count of the number of
processes and threads currently blocked in sem_wait(3). Linux
adopts the former behavior.
sem_getvalue() returns 0 on success; on error, -1 is returned and
errno is set to indicate the error.
EINVAL sem is not a valid semaphore. (The glibc implementation
currently does not check whether sem is valid.)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ sem_getvalue() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
POSIX.1-2008.
POSIX.1-2001.
The value of the semaphore may already have changed by the time
sem_getvalue() returns.
sem_post(3), sem_wait(3), sem_overview(7)
This page is part of the man-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
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⟨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-
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Linux man-pages 6.15 2025-05-17 sem_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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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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