Code Simulation Error during debugging

Florin X Mateoc mateoc_florin at jpmorgan.com
Fri Oct 20 15:23:25 UTC 2000


Hi,

VisualWorks has moved to a process-faithful debugger in 5i. Still, there are
limits to what you can debug (for example debugging the debugger, or debugging
the UI (a different kind of difficulty)).
The fact that Smalltalk reifies so much of its internal machinery allows
programs to know about themselves (and act on themselves too): think Processor
activeProcess, or thisContext. To correctly simulate such an execution the
simulation mechanism has to do something different than just interpreting the
bytecodes.

As an example, in "Processor activeProcess suspend", normal execution should
stop, but when you simulate it, you have two difficulties:
First of all, the simulated execution of "Processor activeProcess" has to be
smart enough to return the simulated process instead of the active one
performing the simulation.
Second, the simulation engine has to recognize that suspend will stop the
simulated process, therefore it should stop simulating it. (if the simulation
merely sends "suspend" to another process, it will then happily continue
simulating what comes after).
I hope this explains a little "simulation semantics versus vm's semantics"

Florin






wnchips at yahoo.com on 10/19/2000 11:58:35 PM

Please respond to squeak at cs.uiuc.edu

To:   squeak at cs.uiuc.edu
cc:   (bcc: Florin X Mateoc)
Subject:  Re: Code Simulation Error during debugging




Hi Larry,

The Squeak debugger, afaik, is a "simulating debugger"
a la Visual Works.  That means, when you run through
the debugger, you're actually doing most of the vm
work (identifying which objects get what messages,
etc.) in Smalltalk, and only invoking the vm when it
comes down to #perform:.  That means that the
simulation semantics and the vm's semantics need to
match, and (apparently) they don't.

Paul

--- Larry Kellogg <lkellogg at soliloquy.com> wrote:
> Hello,
>   I have been playing around with Squeak (2.7 and
> 2.9) and I seem to run
> into Code Simulation errors while trying to debug
> things. It seems to happen
> quite frequently. I'm on a Windows NT machine. I
> don't think I was doing
> anything too radical, just trying to step into or
> over code. Any ideas?
>
>   Regards,
>
>   Larry
>
>


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