void sched_yield() {
thread_t * thr = thr_current();
thr->state = Yielded;
sysc_call(SysSchedule, 0, 0);
return;
}
void sched_schedule() {
// find a thread to schedule. the scheduled thread is removed from the
// queue, and the currently-run thread is re-added to the queue.
spl_lock(&_sched_lock);
thread_t* old = thr_current();
if(old) {
switch(old->state) {
case Runnable:
// don't stop if the thread still has time!
if(old->preempt_at > systime()) {
goto done;
}
break;
case Yielded:
// timeslice is given up.
old->state = Runnable;
break;
default:
// not relevant here.
break;
}
}
// BUG: this algorithm will start to choose the idle thread when
// only one other thread is remaining runnable.
thread_t* thr = sched_choose(old);
if(thr) {
trace("switching: %d:%d (%d)\n", thr->parent->id, thr->id, thr->priority);
thr->preempt_at = systime() + SCHED_TIMESLICE_US;
thr_switch(thr);
sched_remove_unlocked(thr);
if(old)
sched_add_unlocked(old);
goto done;
}
// let things stay as they are if only one thread exists.
if(old->state == Runnable) {
goto done;
}
fatal("no thread left to schedule - this is bad!\n");
done:
spl_unlock(&_sched_lock);
}
void sched_yield() {
thread_t * thr = thr_current();
thr->state = Yielded;
sched_schedule();
}
