sem_getvalue(3)sem_getvalue(3)NAMEsem_getvalue - Gets the value of a specified semaphore (P1003.1b)
SYNOPSIS
#include <semaphore.h>
int sem_getvalue ( sem_t *sem, int *sval);
LIBRARY
Realtime Library (librt.so, librt.a)
PARAMETERS
Specifies a pointer to the semaphore for which a value is to be
returned. References a location to be updated with the value of the
semaphore indicated by the sem argument.
DESCRIPTION
The sem_getvalue function updates a location referenced by the sval
argument with the value of semaphore sem. The updated value represents
an actual semaphore value that occurred during the call, but may not be
the actual value of the semaphore at the time that the value is
returned to the calling process.
If the semaphore is locked, the value returned will either be zero or a
negative number indicating the number of processes waiting for the sem‐
aphore at some time during the call.
RETURN VALUES
On a successful call, a value of 0 (zero) is returned. Otherwise, a
value of -1 is returned and errno is set to indicate that an error
occurred.
ERRORS
The sem_getvalue function fails under the following condition: The sem
argument does not refer to a valid semaphore.
SEE ALSO
Functions: sem_post(3), sem_trywait(3), sem_wait(3)
Guide to Realtime Programming
sem_getvalue(3)