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SEM_GETVALUE(3) Library Functions Manual SEM_GETVALUE(3)

sem_getvalueget the value of a semaphore

#include <semaphore.h>

int
sem_getvalue(sem_t *sem, int *sval);

The sem_getvalue() function sets the variable pointed to by sval to the current value of the semaphore pointed to by sem, as of the time that the call to sem_getvalue() is actually run.

The sem_getvalue() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

sem_getvalue() will fail if:

[]
sem points to an invalid semaphore.

sem_destroy(3), sem_init(3), sem_open(3), sem_post(3), sem_wait(3)

sem_getvalue() conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).

The value of the semaphore is never negative, even if there are threads blocked on the semaphore. POSIX is somewhat ambiguous in its wording with regard to what the value of the semaphore should be if there are blocked waiting threads, but this behavior is conformant, given the wording of the specification.

June 5, 2013 OpenBSD-current