[Cuis-dev] Strange behavior with stepping

[Juan Vuletich]

Hi Folks,

On 8/21/2021 2:22 PM, Phil B via Cuis-dev wrote:
> Gerald,
>
> On Sat, Aug 21, 2021 at 9:04 AM Gerald Klix via Cuis-dev 
> <cuis-dev at lists.cuis.st <mailto:cuis-dev at lists.cuis.st>> wrote:
>
>     Hi Hilaire,
>
>     I only did a short static analysis
>     (a fancy word for looking at the code
>     and scratching your head).
>
>     IHMO there's a race condition:
>
>     WorldMorph>>#runLocalStepMethods
>
>             | stepMessage |
>             [ stepList notEmpty and:
>                 [ stepList first scheduledTime <= nowTime ]]
>                     whileTrue: [
>                             stepMessage _ stepList first.
>
>
>     This piece of code looks at the scheduleTime of the
>     heap's first element then actually retrieves
>     the first element.
>     While this happens the heap in stepList may
>     be changed by adding or removing elements.
>
>
> If that is the issue, I think there's a larger problem to be solved.  
> Morphic is inherently not thread safe so you're dealing with an 
> intractable problem (short of re-architecting Morphic.)    Other than 
> marking a morph for redraw, anything else touching Morphic from a 
> background process needs to be wrapped in UISupervisor 
> whenUIinSafeState: [].

This is of course true!!!
Hilaire, if you are sending any message that alters Morphic state from a 
different process, follow Phil's advice. It might make things more 
complicated, as possibly your process would need to wait until that 
block is effectively run, possibly using a Semaphore.

>
>     Please try the attached method and tell me if it helps.
>
>     @Juan: Even if my change does not fix Hilaire's problem
>     the method should still be changed.
>
>
>     HTH,
>
>     Gerald
>
>
> Thanks,
> Phil

Thanks,

-- 
Juan Vuletich
www.cuis-smalltalk.org
https://github.com/Cuis-Smalltalk/Cuis-Smalltalk-Dev
https://github.com/jvuletich
https://www.linkedin.com/in/juan-vuletich-75611b3
@JuanVuletich

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