sem_getvalue - get the value of a semaphore
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
sem_getvalue() returns 0 on success; on error, -1 is returned and
errno is set to indicate the error.
For an explanation of the terms used in this section, see attributes(7).
- sem is not a valid semaphore. (The glibc implementation currently
does not check whether sem is valid.)
The value of the semaphore may already have changed by the time
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