SEM_GETVALUE(P) POSIX Programmer's Manual SEM_GETVALUE(P)
sem_getvalue - get the value of a semaphore (REALTIME)
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
The sem_getvalue() function shall update the location referenced by the sval argument to
have the value of the semaphore referenced by sem without affecting the state of the sema-
phore. The updated value represents an actual semaphore value that occurred at some
unspecified time during the call, but it need not be the actual value of the semaphore
when it is returned to the calling process.
If sem is locked, then the object to which sval points shall either be set to zero or to a
negative number whose absolute value represents the number of processes waiting for the
semaphore at some unspecified time during the call.
Upon successful completion, the sem_getvalue() function shall return a value of zero. Oth-
erwise, it shall return a value of -1 and set errno to indicate the error.
The sem_getvalue() function shall fail if:
EINVAL The sem argument does not refer to a valid semaphore.
The following sections are informative.
The sem_getvalue() function is part of the Semaphores option and need not be available on
semctl() , semget() , semop() , sem_post() , sem_timedwait() , sem_trywait() , sem_wait()
, the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and The Open Group
Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 SEM_GETVALUE(P)