[Cuis-dev] Strange behavior with stepping

[Phil B]

Gerald,

On Sat, Aug 21, 2021 at 9:04 AM Gerald Klix via Cuis-dev <
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: [].


> 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
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