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: [email protected] [[email protected]] on behalf of Levente Uzonyi [[email protected]] Sent: Monday, December 26, 2011 9:06 PM To: [email protected]; [email protected] 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: [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. >>> >>> -- >>> View this message in context: >>> http://forum.world.st/Destiny-of-changed-update-tp4234693p4234693.html >>> Sent from the Pharo Smalltalk mailing list archive at Nabble.com. >>> >>> >>> . >> > >
