sem_getvalue (3p) - Linux Man Pages
sem_getvalue: get the value of a semaphore (REALTIME)
PROLOGThis manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
sem_getvalue - get the value of a semaphore (REALTIME)
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 semaphore. 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.
The sem_getvalue() function shall fail if:
The sem argument does not refer to a valid semaphore.
COPYRIGHTPortions 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 original Standard can be obtained online at http://www.opengroup.org/unix/online.html .