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.)

However, many single threaded network event loop libraries, as well as GUI
libraries come with their own main loop/event loop. Your program will never
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?

Even if you did something like this,

int main() { while(1) { poll_my_sockets(); do_work(); } }

wouldn't it use 100% of the CPU's time in the main loop? But it appears
that all asynchronous network libraries somehow don't load up the CPU. Yes,
CPU load is the indicator of actual CPU load, and doesn't factor in
anything that's waiting on I/O, but shouldn't just the act of calling the
poll function in an infinite loop still fully load the CPU?
--=20
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