sem_getvalue — get the value of a semaphore
Synopsis
#include <semaphore.h> int sem_getvalue(sem_t *sem, int *sval);
Link with -pthread.
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 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.
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.
Attributes
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
|---|---|---|
| sem_getvalue() | Thread safety | MT-Safe |
Conforming to
POSIX.1-2001, POSIX.1-2008.
Notes
The value of the semaphore may already have changed by the time sem_getvalue() returns.
See Also
Colophon
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Referenced By
sem_close(3), sem_open(3), sem_overview(7), sem_post(3), sem_unlink(3), sem_wait(3).