Re: [Pharo-project] Destiny of changed:/update:

Mon, 26 Dec 2011 18:06:33 -0800 

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: [email protected] 
[[email protected]] on behalf of Levente Uzonyi 
[[email protected]]

Sent: Monday, December 26, 2011 3:10 PM
To: [email protected]
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: [email protected] 
[[email protected]] on behalf of Stéphane Ducasse 
[[email protected]]

Sent: Monday, December 26, 2011 10:56 AM
To: [email protected]
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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