PeekMessage() question.
mgu...@eriador.prime.com
I would like to use PeekMessage() in a yield loop so that other applications
will be able to run while my application is doing some serious number
crunching. However, I have one concern and that has to do with the
WM_QUIT message. Will PeekMessage() remove a WM_QUIT message from the
windows message queue? If it does can I requeue the message? Perhaps
via PostMessage()? Thanks in advance for any help. Marc
----
Two of the worst things we teach our children are that a knowledge of science
is nice but not necessary, and a knowledge of sex is necessary but not nice.
Marc Guyott Constellation Software, Inc. (508) 620-2800
Framingham, Mass. 01701 USA Ext. 3135
mgu...@primerd.prime.com ...!{uunet, decwrl}!primerd.prime.com!mguyott
Mark Epperson
Here is a tried and true way to make sure that you yield properly:
-------- C U T H E R E ------------------------------------------
/*
This is based on information which is not generally
available. Neither PeekMessage() nor Yield() will yield
if there is a message in the applications queue. So...
GetInputState() (which is 3X faster than PeekMessage()) is
used to see if there are any mouse, keyboard or, timer input
records which will result in message being put into your queue. If
this is false the Yield() will probably work and is thus called,
otherwise PeekMessage() is called with the NO_YIELD flag to get
the next message without yielding excessively and that message
is then dispatched. After all messages have been removed then Yield()
is called.
GetInputState() will fail if the input focus changes so...we enter
the PeekMessage() loop every 16th time to handle this eventuality.
NOTE:
This routine will allow your program to have multiple threads
so make sure the approiate controls are disabled or your WinProcs
take this into consideration.
*/
void AplYield()
{
static int delay = 0;
MSG msg;
LPMSG lpMsg;
if (!(delay++ & 0xf) || GetInputState())
{
lpMsg = &msg;
while (PeekMessage(lpMsg, NULL, 0, 0, PM_REMOVE|PM_NO_YIELD))
{
TranslateMessage(lpMsg);
DispatchMessage(lpMsg);
}
}
Yield();
}
Joel Spolsky
>will be able to run while my application is doing some serious number
>crunching. However, I have one concern and that has to do with the
>WM_QUIT message. Will PeekMessage() remove a WM_QUIT message from the
>windows message queue? If it does can I requeue the message? Perhaps
>via PostMessage()?
Well, you can use PeekMessage with the PM_NOREMOVE bit set, and
messages will not be dequeued, or, as you said, you can use
PostMessage to put it back.
--
Joel Spolsky // And these streets, Quiet as a sleeping army
spo...@cs.yale.edu // Send their battered dreams to heaven. _Paul Simon
mgu...@eriador.prime.com
For those who are interested ... Here are some additional responses I
received via email regarding the problem I was experiencing with
PeekMessage(). My thanks to everyone who responded! You're help is greatly
appreciated. Marc
My original question was:
>I would like to use PeekMessage() in a yield loop so that other applications
>will be able to run while my application is doing some serious number
>crunching. However, I have one concern and that has to do with the
>WM_QUIT message. Will PeekMessage() remove a WM_QUIT message from the
>windows message queue? If it does can I requeue the message? Perhaps
>via PostMessage()?
----
Two of the worst things we teach our children are that a knowledge of science
is nice but not necessary, and a knowledge of sex is necessary but not nice.
Marc Guyott Constellation Software, Inc. (508) 620-2800
Framingham, Mass. 01701 USA Ext. 3135
mgu...@primerd.prime.com ...!{uunet, decwrl}!primerd.prime.com!mguyott
----
Subject: Re: PeekMessage() loop.
From: rafe...@oxy.edu (David Ronald Giller)
To: mgu...@eriador.Prime.COM
Organization: Occidental College, Los Angeles, CA 90041
I use a PeekMessage() loop in one of my programs as the main loop, without
any problems. Here is the loop section:
// Main Message Loop:----------------------------------------------------------
while (TRUE)
{
if (PeekMessage(&msg,
NULL,
NULL,
NULL,
PM_REMOVE))
{
if (msg.message == WM_QUIT) // WM_QUIT not checked as special case,
break; // must check explicitly
TranslateMessage(&msg); // Translates virtual key codes
DispatchMessage(&msg); // Dispatches message to appropriate window
}
else
{
CheckPlayingSong(hWnd);
}
}
return (msg.wParam); // Return the value from PostQuitMessage
//-----------------------------------------------------------------------------
This works (or seems to :-) exactly the same as a GetMessage() loop with the
exception that whenever there is free CPU time, the function CheckPlayingSong()
is performed. I BELIEVE that this is the only way to do this.
Hope this helps.
-Dave
David Giller ----- (rafe...@oxy.edu) or (dgi...@oxy.edu) ------------ Box 134
"Some of us wake up -- others roll over." Occidental College
"It's easy to deceive a child." -- John Lydon Los Angeles, CA 90041
----
Subject: Re: PeekMessage() loop.
From: David Ronald Giller <rafetmad%oxy...@RELAY.CS.NET>
Organization: Occidental College, Los Angeles, CA 90041
I don't think you will have to worry too much about the problem with WM_QUIT
(although I could be wrong... I'm no expert!) because of this: Your MainWndProc
is always reentrant. That means, if you are processing some information, and
the user wants to exit, and you recieve the WM_QUIT in the middle of your data-
processing-free-time-via-PeekMessage()-loop (knowatimean?) you can simply
kill that 'process' by terminating the app with a processing of the WM_QUIT.
Here's a better explanation. If you use the SendMessage() function, your
MainWndProc will be stopped where it is, and re-entered (if you sent yourself
a message) with the message you sent. This could be useful if you, say, had
both a menu item and a control to perform a certain task. The menuitem
condition would take care of the actual work. When you push the button, you
might want to show some indicator of what is going on, like setting some
static field on the screen, then performing the action, then setting the
indicator back. well, you would do this by setting the indicator, calling
a SendMessage(hThisWnd, WM_COMMAND, IDM_WHATEVERTHEACTIONIS, wParam, lParam),
then setting the indicator back.
If you need to finish the computation you are doing, you could set a flag during
the loop where the PeekMessage occurs, then at the end of your process, send
yourself a WM_QUIT. if you just post one in the PeekMessage section, you may
find yourself with infinite loop problems.
-Good luck, and I hope this helps you.
-Dave
David Giller ----- (rafe...@oxy.edu) or (dgi...@oxy.edu) ------------ Box 134
"Some of us wake up -- others roll over." Occidental College
"It's easy to deceive a child." -- John Lydon Los Angeles, CA 90041
----