On Mar 14, 2006, at 8:09 PM, Tran Trong Tri wrote:
Hi,
Thanks for answering...But even if those copies are put into a
queue, does that mean they run sequentially one after another
without being interrupted in between like:
...
copy1 done;
copy2 done;
...something else outside that functionF runs..;
copy3;
cop4;
....
a fucntion is not guaranteed unpre-empted, isn't it?
Here's basically how it works in 1.x:
main() {
// init, start, etc.
while(1) {
if (!queueEmpty()) {
runTask(); // pull the next task off the queue and run it
}
else {
sleep();
}
}
}
Take a look at RealMain.nc and sched.c. In reality, it's a little
more complicated than the pseudocode above because you need to make
sure that the testing for an empty queue and going to sleep is an
atomic operation. Otherwise, you might decide that the queue is
empty, have an interrupt fire that posts a task, and then go to sleep
even though the queue is no longer empty.
Since the scheduler runs tasks one-by-one with a single thread of
control, they can't preempt each other.
In 2.x there's a little more mechanism in there for extensible
schedulers.
Phil
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