On Wed, Oct 10, 2012 at 6:49 PM, V G <x.solarwind.x@gmail.com> wrote:
> Hi all, I have a question about CPU load, task scheduling, and how a real
> operating system (like Linux/BSD/QNX) manage threads.
>
> Q: If you write a simple, single-threaded program in C as follows
>
> int main() { while(1); }
>
> and run it on a single core CPU, the CPU load shoots up to 1.00 and stays
> there. Makes sense, as all of the CPU time is spent in this thread. (All =
as
> in almost all, since the operating system's task scheduler and other
> processes have to run as well.)


What you have done is a busy loop, CPU spends all the time in there.


> However, many single threaded network event loop libraries, as well as GU=
I
> libraries come with their own main loop/event loop. Your program will nev=
er
> exit from the main loop unless you kill it, but while the program is
> running, the CPU does NOT appear to be under load. What's going on here?
> How is it that the main loop is running and is responsive, yet the CPU is
> under minimal load?

generally they make use of poll/select
http://www.makelinux.net/ldd3/chp-6-sect-3

or use a thread instead
http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html
--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.