sem_getvalue(3) Library Functions Manual sem_getvalue(3)
NAME
sem_getvalue - get the value of a semaphore
LIBRARY
POSIX threads library (libpthread, -lpthread)
SYNOPSIS
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
DESCRIPTION
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 sem-
aphore with sem_wait(3), POSIX.1 permits two possibilities for the value
returned in sval: either 0 is returned; or a negative number whose ab-
solute value is the count of the number of processes and threads cur-
rently blocked in sem_wait(3). Linux adopts the former behavior.
RETURN VALUE
sem_getvalue() returns 0 on success; on error, -1 is returned and errno
is set to indicate the error.
ERRORS
EINVAL sem is not a valid semaphore. (The glibc implementation cur-
rently does not check whether sem is valid.)
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│ sem_getvalue() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
POSIX.1-2008.
HISTORY
POSIX.1-2001.
NOTES
The value of the semaphore may already have changed by the time sem_get-
value() returns.
SEE ALSO
sem_post(3), sem_wait(3), sem_overview(7)
Linux man-pages 6.9.1 2024-05-02 sem_getvalue(3)
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