yield_tiemslice() gives up any extra cpu time to any other program that needs it. But if no other program does, it will still use 100% (*).

WIP 4.1.13 and later changed it though. (insert angry smiley)

Inside any of your cycles, either the main or the logic one.

Those are two different things. A quick explanation first (I was told this at school 7 years ago, so I might be remembering this all wrong)...

The CPU works in quantums. A quantum is 1 second long (in fact, it is much, much smaller, say 5 microseconds, but 1 second will work for the example). The CPU gives one quantum to your program, then to another, then to another and continues until all have gotten a quantum.

Now, suppose your program needs to read from hd. It executes 0.5 seconds, and ask the hd to read something. Since hd accessing is much slower (suppose it needs 5 seconds), your program stops there. The other 9.5 seconds are lost because it is your quantum and your program is awaiting for the hd to answer. yield_timeslice will tell the CPU that the quantum is over, and so those 9.5 seconds will be given to another process. In fact is keeping the CPU busy.

Sleep, in the other hand, will stop the execution of your program for that amount of time. When the CPU gives you a quantum, you let the quantum pass, sleeping. Since nothing is being executed in the CPU, the load of the CPU lowers.

In other words, yield_timeslice will optimize your CPU usage. Sleep will give it more idling time.

/* sys_directx_yield_timeslice:
 *  Yields remaining timeslice portion to the system.
 */
static void sys_directx_yield_timeslice(void)
{
   Sleep(1);
}

Under Windows, it just calls Sleep... it should work...

As someone said, in the 4.0.x versions, yield_timeslice does Sleep(0) (which has no effect as far as this is concerned) and not Sleep(1), which only 4.1.14 does.

Ah... that explains some... I took the code from 4.1.14. Microsoft said Sleep(0) is enough, but here we discovered that, under VB, you needed at least 5 to get it down. Explains why they are not similar.

(Edited: For unix systems, it uses select).

eeeh so in allegro 4.0.x yield_timslice() is the same as Sleep(0) and in later versions it is Sleep(1) so this is the thing for me to go?

usec is microseconds, not miliseconds... It waits one microsecond for a key input.

There are 1,000 microseconds in a millisecond, and 1,000 milliseconds in a second. Thus, there are 1,000,000 microseconds in a second.

I would have never thought of doing it like that...

Yes.

Under VB, in example, I need a Sleep of 5 at least to drop CPU usage. Neither 0 nor 1 works.

Chris Katko: His statement was completely correct, though not entirely relevant. He was refering to the posix / iso / whatever standard function sleep() without the S capitalized, which takes an integer number of seconds to sleep for. Apparently some standards body thinks its useful.

so Sleep(1) or rest(1) ? ? ?