Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
 
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On 04.10.2010 22:26, Levente Uzonyi wrote:
> On Mon, 4 Oct 2010, Igor Stasenko wrote: > >> On 4 October 2010 22:51, Henrik Sperre Johansen > <[hidden email]> wrote: >> On 04.10.2010 21:47, Igor Stasenko wrote: >>> >>> On 4 October 2010 22:09, Stéphane Ducasse<[hidden email]> >>> wrote: >>>> >>>> so let us know in the bug entry what is the conclusion :) >>>> >>> I think someone should verify my benchmarks i.e. >>> >>> [ self loadsomething ] timeToRun >>> >>> before and after patch. >>> >>> And conclusion is better be written by Henrik, because he's having >>> concerns about speed, >>> while i don't. :) >> >> I already have: >> >> http://code.google.com/p/pharo/issues/detail?id=1628#c13 >> > emm.. wait. > WeakKeyDict should not delete associations with nil-ed keys > automatically, because otherwise > you won't be able to use it in weak finalization scheme. #rehash truncated duplicate nil keys, thus if it was triggered (f.ex. by a manual removal, or adding enough to cause growth) in a thread with priority higher than finalization process (ie ran after GC but before finalization thread), the nil keys could be truncated before finalization being run. An unlikely scenario, I admit, which I guess is why noone encountered it. #grow suffered the same problem. (well, actually, it didn't add any of the nil keyed associations) > > There is two distinct use cases of weak-key dicts: > a) for weak finalization > b) for attaching some extra info(value) per object(key), which can be > automatically discarded once object become garbage > > so, while in case (b) you can mercilessly kill/reuse associations with > nil keys, once they discovered > in case (a) you should preserve them until there is explicit request > from outside to finalize values. months :) > > The need in (a), apparently prohibits from using (b) in most efficient > manner. > So, i think, the solution would be to introduce a specialized weak-key > dicts, which can work much better for (b). The difference between a and b, and the fact Pharo 1.1's implementation severly screws with the performance if b) (and honestly, isn't that good for a) either) is the point I've been trying to make for months now... In Pharo 1.1 we've moved to the other extreme compared to 1.0, nil keys are never removed. b) always works, but a) HAS to be registered to work satisfactory at all. It was changed to do an extra step of keeping finalized assocs in a special state where they can be simply replaced without rehashing after finalization instead of doing rehash, but that's not really the major result of the change. > > > Squeak's implementation works well in both cases. > > > Levente The way I read it (correct me if I'm wrong), the solution in Squeak was adding a finalizer inst var to WeakKeyDictionary, that way you can distinguish the two cases and handle them appropriately. (in addition there were speed improvements for rehashing, growing, etc.) I looked for another solution which would keep WeakKeyDictionary oblivious to whether or not it was being finalized or not and could not find one, thus I think it is worth porting. Keeping the (pardon my fren.. err, norwegian) POS that is currectly in 1.1, or reverting to the 1.0 version for 1.2, is not a good alternative. Cheers, Henry _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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Sorry for the duplications in last mail, there comes a point where I
just think "screw it", stop editing, and just press send :) Cheers, Henry _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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In reply to this post by Levente Uzonyi-2
2010/10/4 Levente Uzonyi <[hidden email]>:
> On Mon, 4 Oct 2010, Igor Stasenko wrote: > >> On 4 October 2010 22:51, Henrik Sperre Johansen > > <[hidden email]> wrote: >> >> On 04.10.2010 21:47, Igor Stasenko wrote: >>> >>> On 4 October 2010 22:09, Stéphane Ducasse<[hidden email]> >>> wrote: >>>> >>>> so let us know in the bug entry what is the conclusion :) >>>> >>> I think someone should verify my benchmarks i.e. >>> >>> [ self loadsomething ] timeToRun >>> >>> before and after patch. >>> >>> And conclusion is better be written by Henrik, because he's having >>> concerns about speed, >>> while i don't. :) >> >> I already have: >> >> http://code.google.com/p/pharo/issues/detail?id=1628#c13 >> > emm.. wait. > WeakKeyDict should not delete associations with nil-ed keys > automatically, because otherwise > you won't be able to use it in weak finalization scheme. > > There is two distinct use cases of weak-key dicts: > a) for weak finalization > b) for attaching some extra info(value) per object(key), which can be > automatically discarded once object become garbage > > so, while in case (b) you can mercilessly kill/reuse associations with > nil keys, once they discovered > in case (a) you should preserve them until there is explicit request > from outside to finalize values. > > The need in (a), apparently prohibits from using (b) in most efficient > manner. > So, i think, the solution would be to introduce a specialized weak-key > dicts, which can work much better for (b). > > > Squeak's implementation works well in both cases. > > called 'well' :) My point is, that these two scenarios should use different classes/implementors each optimized for own case. Moreover, case (b) comes from the inability to dynamically add extra slot(s) to object, which you can easily do in Self or JavaScript, but can't do in smalltalk. > Levente > >> Cheers, >> Henry >> >> _______________________________________________ >> Pharo-project mailing list >> [hidden email] >> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > > > -- -- Best regards, Igor Stasenko AKA sig. _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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In reply to this post by Henrik Sperre Johansen
On Mon, 4 Oct 2010, Henrik Sperre Johansen wrote:
> On 04.10.2010 22:26, Levente Uzonyi wrote: >> On Mon, 4 Oct 2010, Igor Stasenko wrote: >> >>> On 4 October 2010 22:51, Henrik Sperre Johansen >> <[hidden email]> wrote: >>> On 04.10.2010 21:47, Igor Stasenko wrote: >>>> >>>> On 4 October 2010 22:09, Stéphane Ducasse<[hidden email]> >>>> wrote: >>>>> >>>>> so let us know in the bug entry what is the conclusion :) >>>>> >>>> I think someone should verify my benchmarks i.e. >>>> >>>> [ self loadsomething ] timeToRun >>>> >>>> before and after patch. >>>> >>>> And conclusion is better be written by Henrik, because he's having >>>> concerns about speed, >>>> while i don't. :) >>> >>> I already have: >>> >>> http://code.google.com/p/pharo/issues/detail?id=1628#c13 >>> >> emm.. wait. >> WeakKeyDict should not delete associations with nil-ed keys >> automatically, because otherwise >> you won't be able to use it in weak finalization scheme. > It could in 1.0, without anyone noticing. > #rehash truncated duplicate nil keys, thus if it was triggered (f.ex. by a > manual removal, or adding enough to cause growth) in a thread with priority > higher than finalization process (ie ran after GC but before finalization > thread), the nil keys could be truncated before finalization being run. An > unlikely scenario, I admit, which I guess is why noone encountered it. didn't find the cause of the problem, because it was hardly reproducible. Creating a new Socket could trigger #grow in the WeakRegistry's dictionary which could trigger a GC when the new array was allocated. For example ConnectionQueue's #listenLoop uses #highIOPriority (70) and creates new sockets. > #grow suffered the same problem. (well, actually, it didn't add any of the > nil keyed associations) >> >> There is two distinct use cases of weak-key dicts: >> a) for weak finalization >> b) for attaching some extra info(value) per object(key), which can be >> automatically discarded once object become garbage >> >> so, while in case (b) you can mercilessly kill/reuse associations with >> nil keys, once they discovered >> in case (a) you should preserve them until there is explicit request >> from outside to finalize values. > Yes, that's the point I've been trying to make these past couple of months :) >> >> The need in (a), apparently prohibits from using (b) in most efficient >> manner. >> So, i think, the solution would be to introduce a specialized weak-key >> dicts, which can work much better for (b). > The difference between a and b, and the fact Pharo 1.1's implementation > severly screws with the performance if b) (and honestly, isn't that good for > a) either) is the point I've been trying to make for months now... > > In Pharo 1.1 we've moved to the other extreme compared to 1.0, nil keys are > never removed. b) always works, but a) HAS to be registered to work > satisfactory at all. objects := (1 to: 1000) collect: [ :each | Object new ]. dictionary := WeakKeyDictionary new. objects do: [ :each | dictionary at: each put: 1 ]. objects := nil. Smalltalk garbageCollect. counter := 0. dictionary allAssociationsDo: [ :each | counter := counter + 1 ]. self assert: counter = 1000. dictionary rehash. counter := 0. dictionary allAssociationsDo: [ :each | counter := counter + 1 ]. self assert: counter = 1000 "This will fail, because counter = 0." > It was changed to do an extra step of keeping finalized assocs in a special > state where they can be simply replaced without rehashing after finalization > instead of doing rehash, but that's not really the major result of the > change. > >> >> >> Squeak's implementation works well in both cases. >> >> >> Levente > The way I read it (correct me if I'm wrong), the solution in Squeak was > adding a finalizer inst var to WeakKeyDictionary, that way you can > distinguish the two cases and handle them appropriately. (in addition there > were speed improvements for rehashing, growing, etc.) time instead of O(n^2). But it's also handy for doing proper finalization. And there are other improvements, like #remove: triggers the finalizer and cleans up the slots in the removed element's "chain". So both addition (via #grow) and removal of elements can free slots held by GC'd keys. The implementation in Pharo 1.1 still has an O(n^2) issue. Not expired associations with nil keys, are added to the front of the array during #grow (see #noCheckAdd:). The free slot for the association is found by a linear search started from the first slot in the array (OMG). If there are k such elements, then it takes k * (k + 1) / 2 = O(k^2) time. Since k can be n if the dictionary is not registered to the finalization process, this means O(n^2) time: objects := (1 to: 10000) collect: [ :each | Object new ]. dictionary := WeakKeyDictionary new. objects do: [ :each | dictionary at: each put: 1 ]. objects := nil. Smalltalk garbageCollect. counter := 0. dictionary allAssociationsDo: [ :each | counter := counter + 1 ]. self assert: counter = 10000. [ dictionary grow ] timeToRun "===> 1830" Levente > > I looked for another solution which would keep WeakKeyDictionary oblivious to > whether or not it was being finalized or not and could not find one, thus I > think it is worth porting. > Keeping the (pardon my fren.. err, norwegian) POS that is currectly in 1.1, > or reverting to the 1.0 version for 1.2, is not a good alternative. > > Cheers, > Henry > > _______________________________________________ > Pharo-project mailing list > [hidden email] > http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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On 05.10.2010 00:25, Levente Uzonyi wrote:
> On Mon, 4 Oct 2010, Henrik Sperre Johansen wrote: > >> On 04.10.2010 22:26, Levente Uzonyi wrote: >>> On Mon, 4 Oct 2010, Igor Stasenko wrote: >>> >>>> On 4 October 2010 22:51, Henrik Sperre Johansen >>> <[hidden email]> wrote: >>>> On 04.10.2010 21:47, Igor Stasenko wrote: >>>>> >>>>> On 4 October 2010 22:09, Stéphane Ducasse<[hidden email]> >>>>> wrote: >>>>>> >>>>>> so let us know in the bug entry what is the conclusion :) >>>>>> >>>>> I think someone should verify my benchmarks i.e. >>>>> >>>>> [ self loadsomething ] timeToRun >>>>> >>>>> before and after patch. >>>>> >>>>> And conclusion is better be written by Henrik, because he's having >>>>> concerns about speed, >>>>> while i don't. :) >>>> >>>> I already have: >>>> >>>> http://code.google.com/p/pharo/issues/detail?id=1628#c13 >>>> >>> emm.. wait. >>> WeakKeyDict should not delete associations with nil-ed keys >>> automatically, because otherwise >>> you won't be able to use it in weak finalization scheme. >> It could in 1.0, without anyone noticing. >> #rehash truncated duplicate nil keys, thus if it was triggered (f.ex. >> by a manual removal, or adding enough to cause growth) in a thread >> with priority higher than finalization process (ie ran after GC but >> before finalization thread), the nil keys could be truncated before >> finalization being run. An unlikely scenario, I admit, which I guess >> is why noone encountered it. > > That's not true. People experienced the issues (leaking Sockets), but > didn't find the cause of the problem, because it was hardly > reproducible. Creating a new Socket could trigger #grow in the > WeakRegistry's dictionary which could trigger a GC when the new array > was allocated. For example ConnectionQueue's #listenLoop uses > #highIOPriority (70) and creates new sockets. > >> #grow suffered the same problem. (well, actually, it didn't add any >> of the nil keyed associations) >>> >>> There is two distinct use cases of weak-key dicts: >>> a) for weak finalization >>> b) for attaching some extra info(value) per object(key), which can be >>> automatically discarded once object become garbage >>> >>> so, while in case (b) you can mercilessly kill/reuse associations with >>> nil keys, once they discovered >>> in case (a) you should preserve them until there is explicit request >>> from outside to finalize values. >> Yes, that's the point I've been trying to make these past couple of >> months :) >>> >>> The need in (a), apparently prohibits from using (b) in most >>> efficient manner. >>> So, i think, the solution would be to introduce a specialized weak-key >>> dicts, which can work much better for (b). >> The difference between a and b, and the fact Pharo 1.1's >> implementation severly screws with the performance if b) (and >> honestly, isn't that good for a) either) is the point I've been >> trying to make for months now... >> >> In Pharo 1.1 we've moved to the other extreme compared to 1.0, nil >> keys are never removed. b) always works, but a) HAS to be registered >> to work satisfactory at all. > > Um, no. Associations with nil keys are lost during #rehash. So, in short, the 1.1 implementation keeps the worst aspects of 1.0, and adds a few new ones. > >> It was changed to do an extra step of keeping finalized assocs in a >> special state where they can be simply replaced without rehashing >> after finalization instead of doing rehash, but that's not really the >> major result of the change. >> >>> >>> >>> Squeak's implementation works well in both cases. >>> >>> >>> Levente >> The way I read it (correct me if I'm wrong), the solution in Squeak >> was adding a finalizer inst var to WeakKeyDictionary, that way you >> can distinguish the two cases and handle them appropriately. (in >> addition there were speed improvements for rehashing, growing, etc.) > > The original goal of the finalizer was to make finalization run in > O(n) time instead of O(n^2). But it's also handy for doing proper > finalization. And there are other improvements, like #remove: triggers > the finalizer and cleans up the slots in the removed element's > "chain". So both addition (via #grow) and removal of elements can free > slots held by GC'd keys. > > The implementation in Pharo 1.1 still has an O(n^2) issue. Not expired > associations with nil keys, are added to the front of the array during > #grow (see #noCheckAdd:). The free slot for the association is found > by a linear search started from the first slot in the array (OMG). If > there are k such elements, then it takes k * (k + 1) / 2 = O(k^2) > time. Since k can be n if the dictionary is not registered to the > finalization process, this means O(n^2) time: Yeah, I've mentioned that before and didn't want to repeat myself ;) Cheers, Henry _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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In reply to this post by Igor Stasenko
On Tue, 5 Oct 2010, Igor Stasenko wrote:
> 2010/10/4 Levente Uzonyi <[hidden email]>: > On Mon, 4 Oct 2010, Igor Stasenko wrote: > >> On 4 October 2010 22:51, Henrik Sperre Johansen > > <[hidden email]> wrote: >> >> On 04.10.2010 21:47, Igor Stasenko wrote: >>> >>> On 4 October 2010 22:09, Stéphane Ducasse<[hidden email]> >>> wrote: >>>> >>>> so let us know in the bug entry what is the conclusion :) >>>> >>> I think someone should verify my benchmarks i.e. >>> >>> [ self loadsomething ] timeToRun >>> >>> before and after patch. >>> >>> And conclusion is better be written by Henrik, because he's having >>> concerns about speed, >>> while i don't. :) >> >> I already have: >> >> http://code.google.com/p/pharo/issues/detail?id=1628#c13 >> > emm.. wait. > WeakKeyDict should not delete associations with nil-ed keys > automatically, because otherwise > you won't be able to use it in weak finalization scheme. > > There is two distinct use cases of weak-key dicts: > a) for weak finalization > b) for attaching some extra info(value) per object(key), which can be > automatically discarded once object become garbage > > so, while in case (b) you can mercilessly kill/reuse associations with > nil keys, once they discovered > in case (a) you should preserve them until there is explicit request > from outside to finalize values. > > The need in (a), apparently prohibits from using (b) in most efficient > manner. > So, i think, the solution would be to introduce a specialized weak-key > dicts, which can work much better for (b). > > > Squeak's implementation works well in both cases. > > My point is, that these two scenarios should use different classes/implementors each optimized for own case. Moreover, case (b) comes from the inability to dynamically add extra slot(s) to object, which you can easily do in Self or JavaScript, but can't do in smalltalk. It can be done better, with extra VM features, but without those, it's pretty close to best possible solution IMHO. There are already two different classes for a) and b): WeakRegistry and WeakKeyDictionary (and subclasses). Levente > Levente > >> Cheers, >> Henry >> >> _______________________________________________ >> Pharo-project mailing list >> [hidden email] >> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project > > > > -- Best regards, Igor Stasenko AKA sig. _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
Re: Another fixes to finalization (was Re: [update 1.2] #12161 - #12172)
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In reply to this post by Igor Stasenko
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> > Moreover, case (b) comes from the inability to dynamically add extra > slot(s) to object, > which you can easily do in Self or JavaScript, but can't do in smalltalk. > > > > It can be done better, with extra VM features, but without those, it's pretty close to best possible solution IMHO. > There are already two different classes for a) and b): WeakRegistry and WeakKeyDictionary (and subclasses). Igor Levente is right. Having dynamic slots to object is nearly a paradigm shift. So let us focus on what we can do now. Now is there a technical problem to apply the solution implemented by levente in Squeak? Because if not this is what we should do. Stef _______________________________________________ Pharo-project mailing list [hidden email] http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project |
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