NAME
sem_getvalue — get
the value of a semaphore (REALTIME)
SYNOPSIS
[SEM]
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
DESCRIPTION
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.
EXAMPLES
None.
APPLICATION USAGE
The sem_getvalue () function is part of
the Semaphores option and need not be available on all implementations.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
semctl(3), semget(3), semop(3) , sem_post(3), sem_timedwait(3), sem_trywait(3), sem_wait(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <semaphore.h>
CHANGE HISTORY
First released in Issue 5. Included for alignment with the POSIX Realtime Extension.
Issue 6
The sem_getvalue () function is marked as
part of the Semaphores option.
The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Semaphores option.
The sem_timedwait(3) function is added to the SEE ALSO section for alignment with IEEE Std 1003.1d-1999.
The
restrict keyword
is added to the sem_getvalue () prototype for
alignment with the ISO/IEC 9899:1999
(“ISO C99”) standard.
IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 1-2002, item XSH/TC1/D6/54 is applied.
IEEE Std 1003.1-2001 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/115 is applied, updating the ERRORS section so that the [EINVAL] error becomes optional.
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