VM questions

Marcel Weiher marcel at metaobject.com
Wed Jan 3 11:52:42 UTC 2001

Another couple of questions that cropped up while doing the VM and  
translation work:

1.	Polling for events

Squeak seems to poll quite vigorously for events, undeterred by the  
fact that nothing is happening. I also see it sucking significantly  
more CPU in Morphic than in MVC when idle, which doesn't really seem  
to be the desired behavior for an event-based system.  The CPU usage  
for idle Morphic is also somewhat bursty.

Should I simply put it too sleep in the event-getter code if there  
are no events, or is this a bad idea?  I should mention that the VM  
is multi-threaded.

2.	Surfaces

It looks like surfaces are a more general replacement for the  
Display interface allowing multiple native windows.  I've read the  
comments but am not entirely clear what the status is.  Could I  
actually replace the current display output routines with  
surface-oriented stuff and get a working image?  Is there sample  

3.	Misc VM

The code that saves the image directly accesses an char* imageName;  
variable instead of using the provided getter routine for the  
imageName.  Is this intentional or something that should be removed?

Calls from the interpreter to the VM support code sometimes use  
plain msg-sends that are translated to function calls (in the C VM),  
and sometimes use inline C code.  Wouldn't it be better to remove the  
literal C-code and let the translator  take care of it?

4.	Stopping the interpreter

The interpret() loop as it is generated by default is not-stoppable  
outside a setjmp()/longjmp(), meaning that the only way to terminate  
it is to terminate the process, which makes the code after the loop  
somewhat redundant (though harmless).  I've added a flag that is  
checked at the end of a message send and breaks out of the loop with  
a goto for the VM I posted.  Along with the recycling of the buffer  
allocated with sqAllocateMemory this allows new images to be loaded  
into an existing process (one at a time!) with only minor leakage.

Is this actually good enough?  Could it be added as a standard  
feature (I see something like it is there for Mac browseer plugins)?   
After I have stopped the VM, is it possible to initiate a save-imge  
sequence externally?

I am pretty sure I have some more questions, but this is probably  
enough for now.


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