2016-08-31 10:10 GMT+02:00 Glenn Cavarlé <[email protected]>: > Hi all (I was out for some days), >
Hi Glenn > > 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. > 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? > > 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. > > 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. > > 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.
