I just had a little question. How come when I use PeekMessage() in my programs, my app''s CPU Usage shoots upto above 80 (Under Windows Task Manager for WinXP)? If I use GetMessage() it doesn''t even go above 0. I know that PeekMessage() is constantly checking the message queue instead of waiting for a message, but should it be using 80+? Thanks /* I use DirectX 8.1 and C++ (Microsoft Visual C++ 6.0 Professional edition) */

When you use GetMessage your program is effectivly paused until a message arives. The function does not return, so your program is not checking for messages. Because the program is not doing anything at all. It is given no cpu time and is 0.

When you use peekmessage your program is continuosly checking for messages itself, its always active and so uses as much cpu time as the system decided is free.
Its 80 because the cpu time is devided by the number of apps that need it. Run two instances of your test program and they should both get around 40.

HTH

[edited by - empirical on March 20, 2004 7:38:42 AM]

Thats what I figured, just wanted to make sure. Thanks!

/*
I use DirectX 8.1 and C++ (Microsoft Visual C++ 6.0 Professional edition)
*/

If you want to use PeekMessage (for whatever) in a loop, you can call Sleep(0); at the end of the loop to conceed spare cpu time to other processes that might need it (according to the docs the rest of the processes time slice for that round of cpu time is given back to the system if Sleep is called with a parameter of 0)

make sure and only call sleep when you DONT have a message to handle ... you do NOT want to call sleep when you did find and handle a message ... cause you want to keep going through messages for your whole time slice

Isn''t it bad to call Sleep()? I was told that it might sleep longer than the supplied time. Thanks.

/*
I use DirectX 8.1 and C++ (Microsoft Visual C++ 6.0 Professional edition)
*/

For better or worse I tend to do something along the lines of:

while(1) {    while(PeekMessage(&msg,...,PM_REMOVE)) {        TranslateMessage(&msg);        DispatchMessage(&msg);    }    // ... do loop stuff here (processing, rendering etc.)    Sleep(0);} 

This is how I learned to do it:
while(mMsg.message != WM_QUIT)
{
if(PeekMessage(&mMsg, NULL, 0, 0, PM_REMOVE))
{
TranslateMessage(&mMsg);
DispatchMessage(&mMsg);
}
else
{
GameLoop();
}
}

/*
I use DirectX 8.1 and C++ (Microsoft Visual C++ 6.0 Professional edition)
*/

Programmer16, your example is fine, and works fine, but doesn't give up unneeded CPU back to other applications as soon as it could ... so it is less well behaved than it could be. Windows will of course TAKE the cpu away from you when your time slice is over, but you KNOW you do not need it when you have no messages in them message queue, so why not give it back (like th AP above your post does) ...

that's really what this question is all about ... if any program uses your system (and mine for my first 2 years of windows programming - cause I hadn't been sure sleep wouldn't hurt me) - then the CPU meter on that machine will always stay near 100% ... when it shouldn't ... just having a window open that's not doing any work, shouldn't look like it's busy all the time.

Hence the Sleep() call.

heres the codumentation quote strait from microsoft:

quote:
Parameters

dwMilliseconds

(in) Minimum time interval for which execution is to be suspended, in milliseconds.

A value of zero causes the thread to relinquish the remainder of its time slice to any other thread of equal priority that is ready to run. If there are no other threads of equal priority ready to run, the function returns immediately, and the thread continues execution.

A value of INFINITE indicates that the suspension should not time out.

so you see, Sleep(0) is you way of telling the OS - I'm not really busy right now, so let someone else run, but get back to me as soon as you can ...

And the REAL REASON this is a GOOD THING(tm) is because windows IS going to take the CPU away from you anyway, to give other processes a timeslice to run, so wouldn't you rather they start their time slice the MOMENT YOU DON'T NEED THE CPU ... instead of some random time you are busy churning away ... if you give up the cpu, the other processes go ... if that starts when you want it to, it will get back sooner, than if you had spun through your loop an extra 5 ms, THEN windows acted ... cause in that cause, you'd get the CPU back 5 ms later (all other things being equal) - AND the user would wonder why your program is written to always be churning ... when they don't see anything happening ...


[edited by - Xai on March 21, 2004 1:03:55 PM]