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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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SEM_GETVALUE(3) Linux Programmer's Manual SEM_GETVALUE(3)
sem_getvalue - get the value of a semaphore
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
Link with -pthread.
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.1-2001, POSIX.1-2008.
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 release 5.13 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 2021-03-22 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)
Copyright and license for this manual page
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