Chris Muller-3 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@

> > 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
>>
>>
>>
>>
>>
>>

Hi Chris, hi Bert,

if you need an example, well, Etoys/Kedama makes those things in the latest
Trunk version. ;-)

It is not the point whether applications should do this or not but our
recently changed semantics of semaphores might render your image unusable
because of unusual application code. I see an opportunity to improve
Morphics robustness and help users debug their applications without image
freeze/lock out. 

So, I want to discuss here, whether there could be a Notification sent
whenever an object/process starts waiting on a semaphore. :-)

Best,
Marcel



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