[Vm-dev] Win32 Event VM prototype

Andreas Raab andreas.raab at gmx.de
Sat Nov 14 06:02:18 UTC 2009

Folks -

I just finished a prototype of the Win32 event VM to illustrate some of 
the practical impact. It makes a really nice demo:

1) Download the VM from


2) Fire up an image with this VM (I used a trunk image) and execute

    AbstractSound stereoBachFugue play.

3) Observe the sound behavior you get when you:
    * drag the window around
    * go to the system menu
    * click the window close button
In all of the above situations the sound play will be interrupted, 
replaying the current buffer over and over.

4) Execute the following:

    (ProcessorScheduler classPool at: #BackgroundProcess) terminate.

You should see a printf that tells you "entering windows main loop" 
which indicates that you're now running under the new regime.

5) Observe the sound behavior you get when you:
    * drag the window around
    * go to the system menu
    * click the window close button
In all of these situations the sound will now keep playing. There can be 
a temporary hickup due to lack of buffering but other than that 
everything continues smoothly.

For those interested I'm attaching the relevant changes (only for 
playing around; these changes are NOT ready to be integrated). The 
Windows main loop has been changed to read like here:

   /* prepare active process and do first time interpret() for old images */
   /* do not allow recursive interpret() */
   allowInterpret = 0;
   /* interpret() will be left after nuking background process */

   /* now do a classic Windows main loop */
   printf("Entering Windows Main Loop\n");
   SetTimer(stWindow, 1, 50, NULL); /* make sure we interpret() every 
50ms */
   allowInterpret = 1; /* okay to interpret() now */
   while (GetMessage(&msg, NULL, 0, 0) > 0) {

and then you call interpret() whenever you feel like it. I'm doing that 
from MainWndProc in response to Windows messages:

   /* A bit of extra paranoia: I'm not sure if calling interpret()
      through checkForInterrupt() recursion into ioProcessEvents()
      is safe (probably not). */
   if(!inProcessEvents && allowInterpret) interpret();

Of course, this isn't finished yet by any means. There are some odd 
effects when a recursion does happen, and somewhere I'm loosing events. 
But I think it does illustrate the point that I'm trying to make.

BTW, does anyone know if wxSqueak is still active? I think the behavior 
of this VM would be a perfect fit for their needs.

   - Andreas

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