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.
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.
The sem_getvalue() function may fail if:
- The sem argument does not refer to a valid semaphore.
The sem_getvalue() function is part of the Semaphores option and need not be available on all implementations.
semctl(), semget(), semop() , sem_post(), sem_timedwait(), sem_trywait(), sem_wait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>
First released in Issue 5. Included for alignment with the POSIX Realtime Extension.
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() 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 standard.
IEEE Std 1003.1-2001/Cor 1-2002, item XSH/TC1/D6/54 is applied.
IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/115 is applied, updating the ERRORS section so that the [EINVAL] error becomes optional.