sem_getvalue3p
Get the value of a semaphore
Usage
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
Prolog
This 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.
Overview
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.
Return value
Upon successful completion, the sem_getvalue() function shall return a value of zero. Otherwise, it shall return a value of -1 and set errno to indicate the error.
Errors
The sem_getvalue() function may fail if:
- EINVAL
-
The sem argument does not refer to a valid semaphore.
The following sections are informative.
Examples
None.
Application usage
None.
Rationale
None.
Future directions
None.