Unless your model includes a large calculation running in another
thread.  I would *guess* the right way to approach this is for the
calculation-thread to periodically create a custom
display-context-object containing only simple objects like Integers
and Strings, then never touch that object again after assigning it to
an instance variable as an atomic action.  Perhaps a good application
for an immutable object.

cheers -ben

On Tue, Aug 23, 2016 at 12:00 AM, Chris Muller <asqueaker at gmail.com> wrote:
> Morphic is designed to run in one Process, so you shouldn't need any
> multi-process coordination because you should only be doing drawing in
> the UI process.  Right?
>
> On Mon, Aug 22, 2016 at 9:51 AM, Marcel Taeumel <marcel.taeumel at hpi.de> wrote:
>> Hi, there.
>>
>> Take this Morph here:
>>
>> initialize
>>    super initialize.
>>    semaphore := Semaphore forMutualExclusion.
>>
>> step
>>    semaphore critical: [ [] repeat ].
>>
>> drawOn: aCanvas
>>    semaphore critical: [super drawOn: aCanvas].
>>
>> If you create such a morph and open it in the world, the UI process will
>> freeze because of that endless loop in the step method. Okay. The tricky
>> thing is, that you cannot use [CMD]+[.] because the drawing code waits for
>> the same semaphore that is currently used in the morph's step. You will not
>> see a debugger appear. The freshly spawned UI process will block right awai.
>> The well known big red cross/box does not appear because there is no place
>> to detect this situation.
>>
>> An easy fix would be to tell the application developer to use
>> #critical:ifLocked: in that drawing code. If that semaphore is really
>> necessary.
>>
>> However, can there be a way for Morphic to detect such issues and flag that
>> Morph for the big red box? (i.e. "morph setProperty: #errorOnDraw toValue:
>> true") Could there be a notification for the Morphic framework to look out
>> for such as WaitOnCriticalSection to flag that morph as bad? Could that
>> primitive 86 send such a notification efficiently? Just once? ^__^
>>
>> If yes, Morphic could draw its world like this (pseudo code!):
>> ...
>> [aWorld displayWorld] on: WaitOnCriticalSection do: [:err |
>>    err "..." findBadMorph  "..." setProperty: #errorOnDraw toValue: true.]
>> ...
>>
>> Morphic would be more robust.
>>
>> Best,
>> Marcel
>>
>>
>>
>>
>>
>>
>