I did indeed write that weak collections must be thread safe and self-repairing, which is quite correct. It has everything to do with finalization, which can be applied to any object (e.g. the handle body pattern). What good are weak collections if they either prevent garbage collection of their elements (are hence not weak) or can't cope with the finalization of objects that are removed by the garbage collection that they (correctly) did not prevent (incomplete implementation)? Bill ________________________________________ From: pharo-project-bounces@lists.gforge.inria.fr [pharo-project-bounces@lists.gforge.inria.fr] on behalf of Levente Uzonyi [leves@elte.hu] Sent: Monday, December 26, 2011 9:06 PM To: Pharo-project@lists.gforge.inria.fr; andres.valloud@gmail.com Subject: Re: [Pharo-project] Destiny of changed:/update: On Mon, 26 Dec 2011, Andres Valloud wrote:
That's not how ephemerons work, and they also get finalized. Both of you may be right...
Well, yes, with ephemerons you can implement a finalization mechanism which is triggered when the object is _about to be_ garbage collected (note that the finalize() method in java is similar). But it doesn't mean that finalization has anything to do with weak collections or that weak collections should be thread safe, which is what Bill wrote. Levente
On 12/26/11 16:49 , Levente Uzonyi wrote:
On Mon, 26 Dec 2011, Schwab,Wilhelm K wrote:
Levente,
Not meaning to be confrontational, but finalization does not happen "in" any type of collection. It happens *to* elements that can be held in any type of weak collection. As a result, they should all be thread safe and self-repairing.
I guess you're wrong. A weak collection is a collection which doesn't hold strong references to its elements, so they can be garbage collected when there are no other strong references to them. Finalization is a service which triggers an action when an object is garbage collected. Some finalization techniques require the use of weak collections, but otherwise weak collections are independent of finalization.
Levente
Bill
________________________________________ From: pharo-project-bounces@lists.gforge.inria.fr [pharo-project-bounces@lists.gforge.inria.fr] on behalf of Levente Uzonyi [leves@elte.hu] Sent: Monday, December 26, 2011 3:10 PM To: Pharo-project@lists.gforge.inria.fr Subject: Re: [Pharo-project] Destiny of changed:/update:
On Mon, 26 Dec 2011, Schwab,Wilhelm K wrote:
Stef,
I completely agree that events/announcements are cleaner and easier to understand than changed/update. I don't really care whether or not the latter is removed, because I never (directly) use it. Others might prefer to have it retained??
I'm not supposed to say where<g>, but I have seen events, weak collections and finalization done *really* well. In fairness, my working image is old and I need to take another stab at building a recent image, but when I last reviewed them, Pharo's weak collections were lacking features. They have to be thread safe, and they need to clear nil entries left behind by finalization (which is why they must be thread safe). The better we get with events (#on:send:to and friends), the more the current weak collections will appear to be lacking.
Finalization only happens in WeakRegistries and those are thread safe. The other weak collections are not subject to finalization, therefore they don't have to be thread safe, that's why they aren't.
Levente
Bill
________________________________________ From: pharo-project-bounces@lists.gforge.inria.fr [pharo-project-bounces@lists.gforge.inria.fr] on behalf of Stéphane Ducasse [stephane.ducasse@inria.fr] Sent: Monday, December 26, 2011 10:56 AM To: Pharo-project@lists.gforge.inria.fr Subject: Re: [Pharo-project] Destiny of changed:/update:
using on:send: instead of changed/ is a nice way to reduce extra updates. In Cuis juan kept only one mechanism and I like that.
In VisualWorks you have to use on:send:to: this way you can select with facet is refreshed. So I would like to deprecated changed.
Stef
Will changed:/update: disappear and be totally replaced by Announcements?
I ask because I'm using ListModel and noticed that it sends a generic "self changed: #selectionIndex". I built a GUI that had two of them, and couldn't differentiate between the updates, so I was going to enhance it a little.
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