Hi Norbert,

�� �� it is the debugger that needs fixing, not your code !! :-). ��The debugger needs to respect process identity. ��Andreas and I (mostly Andreas) came up with the following changes at Qwaq. ��Your message is a good reminder that I need to add this to Squeak asap.

The idea is for Process to have an additional inst var 'effectiveProcess' that holds the actual process running code. ��For the most part this is self, but in the debugger we substitute the process being debugged:

Process methods for accessing

effectiveProcess

"effectiveProcess is a mechanism to allow process-faithful debugging. ��The debugger executes code

on behalf of processes, so unless some effort is made the identity of Processor activeProcess is not

correctly maintained when debugging code. ��The debugger uses evaluate:onBehalfOf: to assign the

debugged process as the effectiveProcess of the process executing the code, preserving process

identity."

^effectiveProcess ifNil: [self]

then the relevant methods in Process and processorScheduler defer to effectiveProcess, e.g.

ProcessorScheduler methods for process state change

terminateActive

"Terminate the process that is currently running."

activeProcess effectiveProcess terminate

and the debugging methods use evaluate:onBehalfOf: to install the process being debugged:

Process methods for private

evaluate: aBlock onBehalfOf: aProcess

"Evaluate aBlock setting effectiveProcess to aProcess. ��Used

in the execution simulation machinery to ensure that

Processor activeProcess evaluates correctly when debugging."

| oldEffectiveProcess |

oldEffectiveProcess := effectiveProcess.

effectiveProcess := aProcess.

^aBlock ensure: [effectiveProcess := oldEffectiveProcess]

Process methods for changing suspended state

step

^Processor activeProcess

evaluate: [suspendedContext := suspendedContext step]

onBehalfOf: self

stepToCallee

"Step until top context changes"

Processor activeProcess

evaluate:

[| ctxt |

ctxt := suspendedContext.

[ctxt == suspendedContext] whileTrue: [

suspendedContext := suspendedContext step]]

onBehalfOf: self.

^suspendedContext

etc. ��Changes from a Qwaq image attached.

HTH

On Mon, Jun 23, 2014 at 4:50 AM, Norbert Hartl <norbert@hartl.name> wrote:

In my code I'm using a DynamicVariable to request a context object when needed. Until now I knew the name DynamicVariable only from seaside. There it is called WADynamicVariable and it is an exception. So I blindly assumed the pharo DynamicVariable works the same.
I thought this might be a good optimization not to travel the stack all the time but put in the process.
Now that I am using it I can see the difference. I find it real hard using it because I don't know how to debug/step in code. DynamicVariable is a process specific variable but as soon as a debugger opens it is very likely to be in another process. This makes stepping in method using the DynamicVariable impossible. The only way round is to set break points after the dynamic lookup and step from there. But this feels just wrong.
What would be the best way to have DynamicVariable and be able to debug anything? Or is there a variant that uses the stack instead of the "active" process?

thanks,

Norbert

--
best,

Eliot