Manpage of SEM_GETVALUE
SEM_GETVALUESection: Linux Programmer's Manual (3)
NAMEsem_getvalue - get the value of a semaphore
#include <semaphore.h>int sem_getvalue(sem_t *sem, int *sval);
DESCRIPTIONsem_getvalue() places the current value of the semaphore pointed to seminto 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 VALUEsem_getvalue() returns 0 on success; on error, -1 is returned and errnois set to indicate the error.
- semis not a valid semaphore.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
CONFORMING TOPOSIX.1-2001, POSIX.1-2008.
NOTESThe value of the semaphore may already have changed by the time sem_getvalue() returns.
SEE ALSOsem_post(3), sem_wait(3), sem_overview(7)
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