Le 09/08/2011 09:28, Phil Steitz a écrit :
On 8/8/11 10:46 PM, Sébastien Brisard wrote:
2011/8/8 Phil Steitz<phil.ste...@gmail.com>:
+1 to the idea of using the Observer pattern; but -0 for
Observable. I would favor defining Events and Listeners because a)
Observable is concrete, so effectively forces you to create an
Observable delegate
I'm not sure I understand. Components in java.awt also need to
implement quite a few methods like addListener, fireEvent, and so on.
Maybe we could write a DefaultObservable, which would implement most
of the methods required by Observable, and could be inherited by some
(probably not all, unfortunately) of the already implemented iterative
algorithms ?
I was suggesting that we dispense with having anything inherit from
Observable and just define events and listeners, similarly to what
you find in the awt components, but also elsewhere like javax.sql or
javax.servlet (and I am sure lots of other places too). Observable
just gives you hasChanged and a primitive, non-type-safe
notifyListeners. To do proper event propagation you need to define
custom events anyway and register listeners, so unless all you need
to raise are "some state has changed" events (like what a GUI
presentation layer needs from the model in MVC), you are better off
implementing a proper event framework. This does not have to be
heavyweight. Just define
0) Event class(es) extending j.u.EventObject
1) a listener interface extending j.u.EventListener
2) implement addXxxListener, removeXxxListener and
fireInterstingEvent1...n in the class that you want to be observable
(i.e. source events)
Items 0) and 1) and most of 2) are going to be necessary anyway if
you want to propagate typesafe events. All that you really save by
bringing in Observable is maintenance of the listener collection,
which is trivial.
<snip/>
Browsing through the JavaDoc, I realized that o.a.c.m.ode has some
event handling facilities. Is the implementer still around?
That would be Luc.
I'm here.
Sorry for the delay, I am on holidays for three weeks and working in my
house.
When I read the first mail in this thread a few minutes ago, I thought:
this is close to what we have in ODE. Then I remembered a discussion
with Dietmar and Nikolaus when we met at an optimization workshop in
Toulouse: they also raised the need for some monitoring/logging facility
in optimization algorithms. Gilles also raise this problem in this thread.
So I would now say: we do have both an event framework *and* a step
handler framework in ODE, but they are both tailored for ODE.
If we can think of a more general framework, I would say this framework
should be used for all our iterative algorithms and the ODE framework
should be changed to use it too.
So here are the needs for ODE:
- callbacks for regular steps when they complete, without
any feedback with the algorithm. This is now implemented using
StepHandler and FixedStepHandler and the handlerStep method is void,
so from the algorithm point of view this monitoring is almost no-op.
- callbacks for discrete events, which may provide feedback to the
algorithm. This is now implemented using EventHandler and requires
a function to define the event (the g function, events occurring at
sign changes) and a function to be triggered when the events occurs
(the eventOccurred function, which provides the current state and
which return value is used by the algorithm to know what to do next,
i.e. continue/stop/reset state/reset derivatives.
These needs are really, really important and in fact are one of the main
feature in Commons Math ODE (and prior to that from Mantissa) that was
often praised by users.
Do you think we should design something now for 3.0 or should it wait
4.0 ? I would love to have such a new feature soon, but fear it could
delay 3.0 too much.
Luc
Phil
Sebastien
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