/**
* @ingroup monitors
*
* Return a monitor's count
* @param mon target monitor
* @return count from montab entry on success, SYSERR on failure
*/
syscall moncount(monitor mon)
{
if (isbadmon(mon))
{
return SYSERR;
}
return (montab[mon].count);
}
/**
* @ingroup monitors
*
* Current thread attempts to grab the lock on a monitor.
* If another thread does not hold the lock the current thread owns the lock
* and increases the monitor's count by one. Otherwise, the thread waits.
* @param mon target monitor
* @return OK on success, SYSERR on failure
*/
syscall lock(monitor mon)
{
register struct monent *monptr;
irqmask im;
im = disable();
if (isbadmon(mon))
{
restore(im);
return SYSERR;
}
monptr = &montab[mon];
/* if no thread owns the lock, the current thread claims it */
if (NOOWNER == monptr->owner)
{
monptr->owner = thrcurrent; /* current thread now owns the lock */
(monptr->count)++; /* add 1 "lock" to the monitor's count */
wait(monptr->sem); /* this thread owns the semaphore */
}
else
{
/* if current thread owns the lock increase count; dont wait on sem */
if (thrcurrent == monptr->owner)
{
(monptr->count)++;
}
/* if another thread owns the lock, wait on sem until monitor is free */
else
{
wait(monptr->sem);
monptr->owner = thrcurrent;
(monptr->count)++;
}
}
restore(im);
return OK;
}
/**
* @ingroup monitors
*
* Free a monitor previously allocated with moncreate().
*
* A monitor must only be freed when no thread has it locked -- that is, either
* the monitor is unowned, or is owned by a thread that has been killed.
*
* @param mon
* The monitor to free.
*
* @return
* ::OK on success; ::SYSERR on failure (@p mon did not specify a valid,
* allocated monitor).
*/
syscall monfree(monitor mon)
{
struct monent *monptr;
irqmask im;
im = disable();
/* make sure the specified monitor is valid and allocated */
if (isbadmon(mon))
{
restore(im);
return SYSERR;
}
monptr = &montab[mon];
/* free the monitor's semaphore and mark the monitor table entry as free */
semfree(monptr->sem);
monptr->state = MFREE;
restore(im);
return OK;
}
