Manual Section... (3) - page: sem_getvalue
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 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.1-2001 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 errno is set to indicate the error.
- sem is not a valid semaphore.
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)
COLOPHONThis page is part of release 3.24 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.
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Time: 15:27:08 GMT, June 11, 2010