<br><br><div class="gmail_quote">On Fri, Jun 7, 2013 at 2:34 AM, Camille Teruel <span dir="ltr"><<a href="mailto:camille.teruel@gmail.com" target="_blank">camille.teruel@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word"><div> On 7 juin 2013, at 11:19, Pharo Issue Tracker wrote:<div><br><blockquote type="cite"><div>A FogBugz case was edited by Stephane Ducasse.<br><br>Case ID: 10840<br>Title: WeakSet>>#size utterly broken<br>
Status: Resolved (Fix Review Needed)<br>Category: Bug<br>Project: Collection<br>Area: Misc<br>Priority: 3 - Must Fix<br>Milestone: Pharo3.0: 30/03/2014<br>Assigned To: Camille Teruel<br><br>
URL: <a href="https://pharo.fogbugz.com/f/cases/10840" target="_blank">https://pharo.fogbugz.com/f/cases/10840</a><br><br>Last message:<br>Please can you send a mail to the mailing-list so that we all discuss this problems.<br>
</div></blockquote><br><div>Hello everyone,<div><br></div><div>WeakSet>>#size is broken as demonstrated by the following snippet:</div><div><br></div><div>set := WeakSet new.</div><div>set add: Object new.</div><div>
Smalltalk garbageCollect.</div><div>set size. "answers 1 instead of 0"</div><div><br></div><div>That is because a WeakSet has no mean to know when its items get garbage collected, and thus the tally cannot be updated.</div>
<div>So we need to override #size in Weak, I propose:</div><div><div>size</div><div><span style="white-space:pre-wrap"> </span>| counter |</div><div><span style="white-space:pre-wrap"> </span>counter := 0.</div><div><span style="white-space:pre-wrap"> </span>self do: [ :e | counter := counter + 1 ].</div>
<div><span style="white-space:pre-wrap"> </span>^ counter</div></div><div>But that it rather inefficient for such a simple query.</div><div><div>Any proposition?</div></div></div></div></div></div></blockquote><div><br></div>
<div>One way is to add WeakSets to FInalizationDependents and implement finalizeValues to update the size. But that's making work. A lazy solution might be better.</div><div><br></div><div>You *could*, I suppose, use the VM's count of the number of incremental and full GCs (alas there's no single count). I think this is too ugly and one would need something neater, but it would work like this:</div>
<div><br></div><div>size</div><div> | newGCCount |</div><div> newGCCount := self getGCCount.</div><div> newGCCount == existingGCCount ifTrue:</div><div> [^tally].</div><div> tally := self computeActualSIze.</div>
<div> existingGCCount := newGCCount</div><div><br></div><div>where</div><div> getGCCount</div><div> ^(Smalltalk vmParameterAt: 7) + (Smalltalk vmParameterAt: 9)</div><div> </div><div>There are obviously thread-safety issues here, but there are issues with the existing code and your suggestion too ;)</div>
<div><br></div><div>The most useful single count here would be a count that was incremented once in each GC that finalized one or more references.</div><div><br></div><div>Note also that for this to be reliable instances' record of the count would have to be invalidated on snapshot or start-up, which could entail an expensive allInstancesDo:.</div>
<div><br></div><div>Perhaps the class WeakSet should maintain its instances in (of course) a WeakSet and then add only itself to FinalizationDependents and enumerate the set on finalization?</div><div><br></div><div><br></div>
<div><br></div><div>I note that in the VisualWorks VM, objects that have references finalized are added to a queue so every instance that loses a reference gets sent finalize, instead of only dependents as in Squeak. This has its won problems (the VM must cope with a potentially large list) but I think it provides more convenient control.</div>
<div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><div><div><div><div><br></div><div>The bug entry is: <a href="https://pharo.fogbugz.com/f/cases/10840" target="_blank">https://pharo.fogbugz.com/f/cases/10840</a></div>
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</div></blockquote></div><br></div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br>best,<div>Eliot</div>