Opps, I forgot a line in one of the files. Here are the correct versions.
On 8/5/06, Michael D. Adams <[EMAIL PROTECTED]> wrote:
Attached is a draft of the solution for event handlers. I wanted to
put it up for others to get one last chance to comment on before I
commit it.
I wasn't sure what the most appropriate place to put
RegisterWeakListener. I've put it in include/csutil/event.h for now
unless there is a better place someone can point out.
The three files are:
* weak-listener.patch - the core code,
* weak-listener-engine-example.patch
- an example of using RegisterWeakListener in "plugins/engine/3d/engine.h",
* weak-listener-graph2d-example.patch
- an example of using RegisterWeakListener in
"include/csplugincommon/canvas/graph2d.h".
Michael D. Adams
[EMAIL PROTECTED]
On 8/4/06, Jorrit Tyberghein <[EMAIL PROTECTED]> wrote:
> None of these solutions really sound very attractive I must say. I
> wonder if we perhaps should concentrate our solution only on the most
> common type of callback (event handler) and then just use embedded
> interfaces (or separate classes as is also commonly done) for the
> others.
>
> Unless someone can still come up with a workable solution.
>
> Greetings,
>
> On 8/4/06, Michael D. Adams <[EMAIL PROTECTED]> wrote:
> > I like your idea of generalizing this solution to enable weak
> > callbacks in general, but am unable to think of a satisfactory way to
> > do that. In pricipal it is easy, but the limitations of C++ would
> > require writting redirection functions for every function in the
> > interface. I can't think of a clean way to to that automaticly.
> >
> > Let me brainstorm here for a bit. None of the following ideas
> > actually work (well some would work but are probably distatefull), but
> > maybe they will stimulate an idea in someone.
> >
> > Idea 1:
> > Add some wrapper layer to C++ that would allow the following:
> > template<typename T>
> > class csWeakCallback : T
> > {
> > T *imp;
> > public:
> > csWeakCallback (T *imp) : imp(imp) { }
> > <%for $func in functions_of(T)%>
> > $func () { imp->$func(); }
> > <%end for%>
> > };
> >
> > Idea 1.5:
> > The same as Idea 1, but use the preprocessor to do that. (Still
> > probably not possible b/c the preprocessor would need to be able to
> > figure out what functions a particular interface had.)
> >
> > Idea 2:
> > Find some way to take a pointer to a call back interface (e.g.
> > iEventHandler*) and produce another pointer to that interface with the
> > same vtable except for the entries for IncRef and DecRef which would
> > get assigned to no-op functions.
> >
> > Idea 3:
> > Establish some way to "poison" the csRefs that are used internally by
> > what ever the callback is registered with.
> >
> > Idea 3a: Establish some kind of weak-object system so csRef could tell
> > that the pointer it is holding is to an object that should always be
> > held only weakly.
> >
> > Idea 3b: Make a "poisoned" csRef that would poison any csRef that it
> > gets assigned to (poisioned = hold the object only weakly). Then when
> > registering the callback use a csRef instead of a pointer which we
> > will pre-poison.
> >
> > On 8/4/06, Jorrit Tyberghein <[EMAIL PROTECTED]> wrote:
> > > I just considered something. I think this solution is focusing too
> > > much on event handlers but event handlers are not the only type of
> > > callback where this problem occurs. I can't give examples right now
> > > but I'm sure there are many other types of callbacks where similar
> > > problem occurs right now which is also solved with embedding
> > > interface. So perhaps we should find a way to generalize this so that
> > > it can work for a general callback type system?
> > > Perhaps using a template?
> > >
> > > Greetings,
> > >
> > > On 8/3/06, Michael D. Adams <[EMAIL PROTECTED]> wrote:
> > > > On 7/29/06, Jorrit Tyberghein <[EMAIL PROTECTED]> wrote:
> > > > > > *token = new csWeakEventHandler(listener);
> > > > >
> > > > > This is invalid code. You can't use a weak ref like that. Keep in mind
> > > > > that if the only thing that holds a reference to something is a weak
> > > > > reference then the object will be removed. You'll have to rework the
> > > > > code a bit so that after allocation you have a real reference for a
> > > > > while and then you release that reference as soon as you register to
> > > > > the event registry.
> > > > >
> > > > > I do understand the basic idea of your solution though and it seems
> > > > > like a possibility.
> > > >
> > > > Below is a redraft of the code. I changed two things. But I'm not
> > > > sure whether I am using csHandlerID correctly for the second change.
> > > >
> > > > First, I fixed my use of csRef as Jorrit noted should be done.
> > > >
> > > > The second change is to make the csWeakEventListener completely
> > > > invisible to the client code. Now the csHandlerID that is handed back
> > > > (by RegisterListener via RegisterWeakListener) is used to lookup the
> > > > iEventHandler (really a csWeakEventListener) that should be passed on
> > > > to RemoveListener by RemoveWeakListener. (As a side benefit, this
> > > > eliminates the need for an output parameter in RemoveWeakListener to
> > > > hand back the "csRef<csWeakEventListener>*".)
> > > >
> > > > As far as I can tell, there are two kinds of csHandlerID, generic and
> > > > instance. The csHandlerID returned by RegisterListener is an instance
> > > > csHandlerID. What I'm not 100% sure on is that "instance" in this
> > > > context means "per object instance". If it doesn't, then this code
> > > > probably wont work and I should go back to handing back a
> > > > "csRef<csWeakEventListener>*". So can anyone confirm that
> > > > understanding of "instance csHandlerID"?
> > > >
> > > > Michael D. Adams
> > > > [EMAIL PROTECTED]
weak-listener.patch
Description: Binary data
weak-listener-engine-example.patch
Description: Binary data
weak-listener-graph2d-example.patch
Description: Binary data
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