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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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 *sem, int *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)
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Linux 2020-06-09 SEM_GETVALUE(3)
Pages that refer to this page: sem_close(3) , sem_open(3) , sem_post(3) , sem_timedwait(3) , sem_trywait(3) , sem_unlink(3) , sem_wait(3) , sem_overview(7)
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