2016-08-31 10:10 GMT+02:00 Glenn Cavarl�� <glenn.cavarle@gmail.com>:

Hi all (I was out for some days),

Hi Glenn

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What i see is that Bloc EventRegistry:
1) is not thread safe (no mutex + #select:thenDo:)
2) doesn't allow handler removal from the handler list currently used in the
thenDo: loop
3) is used specifically for a one-to-many communication (1 BlElement -> X
handlers)

The (1) doesn't seem to be a problem in Bloc during UI event processing
because a new event handler, even if it is added from another thread, would
be taken into account for the next event.

Problem that concurrent modification of OrderedCollection could just fail. You will got debugger.

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I note that it is really not
recommended (at all) to update an UI element elsewhere than in the UI thread
and it is like that in all other UI frameworks i know.

Does it means that I should not subscribe on UI events from different (not UI) processes?

How to do this if it is needed?��

Should I always put subscription code into #defer: message (analogue)?��

In that case what to do if I need to be sure that I really subscribe on event and only after this continue my business logic process?

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The (2) is a very specific use case and i don't know if it is a real need in
Bloc because this implies that an element has 2 handlers for the same event
and one of them has to remove the other before it is executed and during the
same event processing (maybe more a conception issue than a common use
case...). In other cases, no problem for handler removal.

Very simple example: I want one shot handler for MouseMove to highlight element once to see that my mouse was moved around.

So my handler will highlight target element and unsubscribe it immediately.

Problem that if you do it on OrderedCollection during iteration you could skip one of the handlers. And probably some failures are also possible (debugger again).

Of course you could say users do not do all of this. But what the alternative? And if people will do this by "incident" it will be very difficult to discover reasons.

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But maybe i miss some specific cases in (1) and in (2).

To me, Announcer is really usefull and efficient when it is used as an event
bus that can be shared between multiple objects.
For instance, it seems to be useless to use an Announcer in NewValueHolder
because it cannot be shared and it is only used internally to register
handlers and to propagate only the same event (ValueChanged) to them. What
is the gain of using a full featured Announcer in this case?

But in practice we never share any announcer instance. We always hide it inside owner object. ValueHolder is not specific example.

Also ValueHolder is kind of active model for UI application which could be shared between different views. And when it will be modified in one view another view will be updated automatically.

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In Bloc the constraint is to propagate more than 2000 events/second without
to decrease fps, so we cannot afford to x4 the time to process events even
if Announcer is safer and better tested.

I wondering what the source of this constraint? Does Morphic follows it? I guess not, but all Pharo works quite well with it.��