June 2018 - Pharo-dev - lists.pharo.org

[Pharo 7.0-dev] Build #1106: 22215-Package-System-Support-Traits-could-possibly-get-removed
by ci-pharo-ci-jenkins2＠inria.fr June 30, 2018

June 30, 2018

There is a new Pharo build available! The status of the build #1106 was: SUCCESS. The Pull Request #1614 was integrated: "22215-Package-System-Support-Traits-could-possibly-get-removed" Pull request url: https://github.com/pharo-project/pharo/pull/1614 Issue Url: https://pharo.fogbugz.com/f/cases/22215 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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[Pharo 7.0-dev] Build #1105: 21207-Halo-description-is-almost-invisible-in-the-Help-browser
by ci-pharo-ci-jenkins2＠inria.fr June 30, 2018

June 30, 2018

There is a new Pharo build available! The status of the build #1105 was: SUCCESS. The Pull Request #1424 was integrated: "21207-Halo-description-is-almost-invisible-in-the-Help-browser" Pull request url: https://github.com/pharo-project/pharo/pull/1424 Issue Url: https://pharo.fogbugz.com/f/cases/21207 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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Re: [Pharo-dev] Why do we have SmallDictionary?
by ClÃ©ment Bera June 30, 2018

June 30, 2018

Thanks for the detailed answer. I now understand better why Smalltalk dictionaries are this way. Best, On Sat, Jun 30, 2018 at 2:05 AM, Levente Uzonyi <leves(a)caesar.elte.hu> wrote: > On Fri, 29 Jun 2018, ClÃ©ment Bera wrote: > > Do you guys agree with this? >> > > Mostly. I don't think open addressing's performance is proporional to > loadFactor / (1 - loadFactor). That formula would be correct if you had a > an array filled up to loadFactor randomly, but linear probing creates > longer chains due to clustering, so it's worse than that in practice. > Here's a small table based on my measurements: > > lf formula measurement > 0.5 1.0 ~1.5 > 0.55 1.222 ~1.96 > 0.6 1.5 ~2.62 > 0.65 1.857 ~3.56 > 0.7 2.333 ~5.06 > 0.75 3.0 ~7.5 > 0.8 4.0 ~12.0 > > In Squeak load factor normally varies between 0.5 and 0.75, but it can be > anything between 0.0 and 0.8 (only compaction can push load factor above > 0.75), so performance can differ quite a bit. Based on these numbers 0.7 > sounds like a reasonable upper limit - something we might want to consider. > You might think that linear probing's clustering effect costs too much, > but because of cache locality this is probably still faster than linked > lists or double hashing. > > It is also irrelevant if you can store more elements than the size of the > hash table, because that breaks the precondition of the use of hash tables, > therefore the contract too. So, the promised O(1) runtime of operations is > also gone in that case. > > Finally, removals do not clog the hash tables using open addressing unless > you use lazy deletion[1], which is something you should avoid. > > >> Their open addressing implementation is slightly different from the >> Smalltalk one (they have deleted entries upon removal while we fix >> collisions, >> at least in Pharo 6). >> > > Proactively removing the garbage - aka #fixCollisionsFrom: - takes O(chain > length) time, which is amortized O(1) if your hash function is good enough. > Lazy deletion degrades lookup performance over time, because lookups have > to treat deleted entries as existing entries. It makes deletion somewhat > quicker, because you can stop the lookup procedure as soon as you find your > element, but what you save is amortized O(1). > > Their chaining implementation does not use balanced binary tree when a >> bucket becomes large like Java's implementation. >> > > Because hash tables in general don't do such thing. During my time at the > university, it was one of the tricky questions why hash tables use linked > lists instead of balanced binary trees for collision resolution. > The answer is that you don't need them, because the contract of hash > tables is that you'll (practically) not have long chains if your hash > function is good enough. > Using binary trees for collision resolution mitigate situations when your > hash function is not good enough or when you don't have full control over > your hash values. But those are fairly rare in practice, and you still lose > the O(1) operation runtime cost. > Binary trees also require your elements to have a total order defined on > them. > > >> I don't really understand why an open addressing implementation is >> trickier to implement, in high level languages such as Smalltalk I may agree >> that it might be easier to implement chaining, but in low level language >> such as in the VM, IMO open addressing is easier since you've got only >> one large chunk of memory to manage. Maybe it's because of hash >> collisions, having good hash and good hash collection size >> (See HashTableSizes) is >> not that easy. >> > > It's easy to make indexing mistakes, especially when wrap-around is > involved. Also, deletion is tricky and is often left as an exercise for the > reader. Even the wikipedia article[2] has quite complex pseudocode for it. > The version you find in Squeak has a few hidden tricks too, but those are > there for performance and the code would still work without them. > > Levente > > [1] https://en.wikipedia.org/wiki/Lazy_deletion > [2] https://en.wikipedia.org/wiki/Open_addressing > > > >> I'm curious because I do more and more bare metal programming and I end >> up having to implement this kind of things myself, I've always implemented >> naive open addressing up until now without really understanding details. >> >> [1] http://www.algolist.net/Data_structures/Hash_table/Open_addressing >> >> On Sat, Jun 16, 2018 at 8:49 PM, Max Leske <maxleske(a)gmail.com> wrote: >> >> >> On 8 Jun 2018, at 09:48, StÃ©phane Rollandin wrote: >> >> FWIW it seems there is no SmallDictionary in Squeak. >> >> >> Oh... Thanks StÃ©f, I wasn't aware of that. >> >> >> >> On 8 June 2018, at 15:13, John Brant wrote: >> >> Is anyone aware of a reason for hanging on to >> SmallDictionary? I'm also curious to know how >> SmallDictionary came to be. There must have been >> some advantage over Dictionary at some point in >> the past. >> >> >> It came from RBâ¦ the idea was that there are (in the >> Refactoring engine) a lot of very small dictionaries with >> <10 elements. >> The idea is that for such dictionaries, the overhead of >> hashing was higher than just linear search. >> >> >> I created its ancestor in VW some 20+ years ago (as RBSmallDictionary). >> It was used when doing pattern matching. When it performs a pattern >> match against an AST, it puts the potential value of the pattern >> variable in the dictionary. If the value is used later in the pattern, >> then we can get the previous value and make sure that we have an >> equivalent AST. This allows you to write patterns like: >> >> `@a = `@a >> >> to find where someone has the same expression on both sides of the #= >> message. Since most patterns have very few pattern variables, these >> dictionaries won't hold many entries. Furthermore, we are likely to >> abort the match when we have 0 entries. >> >> The original RBSmallDictionary had an #empty method that "emptied" the >> dictionary without actually removing any elements -- it just set the >> size to 0. In a general dictionary this would lead to memory leaks since >> the previous values are still held by the dictionary. However, these >> dictionaries were only used during the matching process and went away >> after the process completed. >> >> Anyway, at the time when we converted our pattern matching code from >> using the VW parser with our pattern matching extensions to use the new >> RB parser with pattern matching, the time to run Smalllint on the image >> was cut in half even though our parser was quite a bit slower than the >> VW parser. I don't remember everything that was done, but I think that >> most of the speedup came from having special pattern AST nodes and the >> small dictionary. >> >> >> John Brant >> >> >> >> Very interesting! Thanks John! >> >> As Marcus has mentioned before in this thread, it would make a lot of >> sense to run benchmarks again. Actually, I think it would be nice to >> have a benchmark suite for these cases, that would let us monitor the >> performance and ensure that changes to the codebase don't have a >> deteriorative effect. I'm not saying that it would be easy to make this >> happen, writing proper benchmarks is hard (for me especially, as it >> seems, given my utter failure to think of the edge cases before starting >> this thread). Such a suite might also prevent these sorts of >> questions on the mailing list in the future, or at least might make it >> easier to answer them. >> >> >> >> >> On 8 June 2018, at 13:01, Andres Valloud wrote: >> >> In addition, open addressing with linear probing has superior cache >> line read behavior (no indirection / random traversal, and >> if the first probe misses the second one was likely cached by the >> first one). >> >> >> >> Ah, nice catch! Although that would require frequent access to the >> dictionary / repeated access to the same items to have an effect, >> wouldn't it? >> >> >> On 8 Jun 2018, at 10:01, ClÃ©ment Bera wrote: >> >> Hi Max, >> >> Theoretically, for a small number of elements, usually somewhere >> between 3 >> and 30 depending on implementations, a linear search is faster than >> a hash >> search, especially in the Pharo dictionary hash search >> implementation. >> >> Efficient dictionary implementations are usually bucket-based. The >> dictionary holds a certain number of buckets, and based on the key >> hash, >> the bucket where the key value is present is determined. Small >> buckets are >> linear (arrays or linked list). Large buckets are typically >> balanced binary >> trees (red-black trees typically). Under a certain number of >> elements there >> is a single bucket, which means a linear search is performed, as >> for the >> SmallDictionary. When it grows the dictionary search becomes a >> combination >> between a hash search and a linear or tree search. >> >> Pharo dictionary search is first hash-based, then all the buckets >> are >> represented next to each other in the same arrays and a linear >> search is >> performed there, leading to many collisions and slower search time >> (especially when the element is not found), sometimes the code >> searches >> over multiple buckets because the dictionary is too full or there >> are too >> many near-collisions. The memory consumption is competitive with the >> advanced implementations though (precise measurements would need to >> be >> made). >> >> Method dictionaries are represented differently to optimize the >> look-up >> logic. >> >> If you want to improve things and have one dictionary implementation >> instead of two, implement or look for a bucket based dictionary and >> put it >> in the base image instead of Dictionary. This is quite some work >> since >> there are many APIs to port. You can look at the Pinnochio >> implementation, >> it's quite good but they've not implemented large buckets. >> >> >> Thanks for the detailed explanations ClÃ©ment and Levente. I'll probably >> not add a new dictionary implementation ;) >> >> >> >> >> On Fri, Jun 8, 2018 at 8:46 AM, Max Leske <maxleske(a)gmail.com> >> wrote: >> >> Hi, >> >> I was messing around with SmallDictionary when I suddenly >> realised that I >> can't find a single reason to use it over a normal >> Dictionary. While its >> name and class comment imply that it is somehow an optimised >> Dictionary, I >> don't see any measurement where that actually holds up. The >> following was >> run in a Pharo 7 image on a recent VM (see below): >> >> | d | >> d := SmallDictionary new. >> d sizeInMemory. "24" >> [100000 timesRepeat: [ >> 1 to: 100 do: [ :i | d at:i put: i] ] ] timeToRun. >> "0:00:00:05.226" >> >> [100000 timesRepeat: [ >> d at: 48 ifAbsent: [] ] ] timeToRun. "0:00:00:00.041" >> >> >> >> | d | >> d := Dictionary new. >> d sizeInMemory. "16" >> [100000 timesRepeat: [ >> 1 to: 100 do: [ :i | d at:i put: i] ] ] timeToRun. >> "0:00:00:00.385" >> [100000 timesRepeat: [ >> d at: 48 ifAbsent: [] ] ] timeToRun. "0:00:00:00.006" >> >> >> As you can see, SmallDictionary is 8 bytes larger per >> instance and >> significantly faster while reading and writing (I know that >> this isn't a >> good benchmark but it suffices to make my point). >> >> >> Is anyone aware of a reason for hanging on to >> SmallDictionary? I'm also >> curious to know how SmallDictionary came to be. There must >> have been some >> advantage over Dictionary at some point in the past. >> >> >> Cheers, >> Max >> >> >> >> >> >> Image version: Pharo 7.0 >> Build information: Pharo-7.0+alpha.build.961.sha. >> a69e72a97136bc3f93831584b6efa2b1703deb84 (32 Bit) >> >> VM version: CoInterpreter VMMaker.oscog- nice.2281 uuid: >> 4beeaee7-567e-1a4b-b0fb-bd95ce302516 Nov 27 2017 >> StackToRegisterMappingCogit VMMaker.oscog-nice.2283 uuid: >> 2d20324d-a2ab-48d6-b0f6-9fc3d66899da Nov 27 2017 >> VM: 201711262336 https://github.com/OpenSmallta >> lk/opensmalltalk-vm.git $ >> Date: Mon Nov 27 00:36:29 2017 +0100 $ Plugins: 201711262336 >> https://github.com/OpenSmalltalk/opensmalltalk-vm.git $ >> >> OS: macOS 10.13.5 >> Machine: MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports) >> >> >> >> >> -- >> ClÃ©ment BÃ©ra >> https://clementbera.github.io/ >> https://clementbera.wordpress.com/ >> >> >> >> >> >> >> >> -- >> ClÃ©ment BÃ©ra >> https://clementbera.github.io/https://clementbera.wordpress.com/ >> >> -- ClÃ©ment BÃ©ra https://clementbera.github.io/ https://clementbera.wordpress.com/

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Why do we have SmallDictionary?
by Max Leske June 29, 2018

June 29, 2018

Hi, I was messing around with SmallDictionary when I suddenly realised that I can't find a single reason to use it over a normal Dictionary. While its name and class comment imply that it is somehow an optimised Dictionary, I don't see any measurement where that actually holds up. The following was run in a Pharo 7 image on a recent VM (see below): | d | d := SmallDictionary new. d sizeInMemory. "24" [100000 timesRepeat: [ 1 to: 100 do: [ :i | d at:i put: i] ] ] timeToRun. "0:00:00:05.226" [100000 timesRepeat: [ d at: 48 ifAbsent: [] ] ] timeToRun. "0:00:00:00.041" | d | d := Dictionary new. d sizeInMemory. "16" [100000 timesRepeat: [ 1 to: 100 do: [ :i | d at:i put: i] ] ] timeToRun. "0:00:00:00.385" [100000 timesRepeat: [ d at: 48 ifAbsent: [] ] ] timeToRun. "0:00:00:00.006" As you can see, SmallDictionary is 8 bytes larger per instance and significantly faster while reading and writing (I know that this isn't a good benchmark but it suffices to make my point). Is anyone aware of a reason for hanging on to SmallDictionary? I'm also curious to know how SmallDictionary came to be. There must have been some advantage over Dictionary at some point in the past. Cheers, Max Image version: Pharo 7.0 Build information: Pharo-7.0+alpha.build.961.sha.a69e72a97136bc3f93831584b6efa2b1703deb84 (32 Bit) VM version: CoInterpreter VMMaker.oscog- nice.2281 uuid: 4beeaee7-567e-1a4b-b0fb-bd95ce302516 Nov 27 2017 StackToRegisterMappingCogit VMMaker.oscog-nice.2283 uuid: 2d20324d-a2ab-48d6-b0f6-9fc3d66899da Nov 27 2017 VM: 201711262336 https://github.com/OpenSmalltalk/opensmalltalk-vm.git $ Date: Mon Nov 27 00:36:29 2017 +0100 $ Plugins: 201711262336 https://github.com/OpenSmalltalk/opensmalltalk-vm.git $ OS: macOS 10.13.5 Machine: MacBook Pro (13-inch, 2016, Four Thunderbolt 3 Ports)

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[Pharo 7.0-dev] Build #1104: 22174-Remove-FileDoesNotExistExceptiondefaultAction
by ci-pharo-ci-jenkins2＠inria.fr June 29, 2018

June 29, 2018

There is a new Pharo build available! The status of the build #1104 was: SUCCESS. The Pull Request #1573 was integrated: "22174-Remove-FileDoesNotExistExceptiondefaultAction" Pull request url: https://github.com/pharo-project/pharo/pull/1573 Issue Url: https://pharo.fogbugz.com/f/cases/22174 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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[Pharo 7.0-dev] Build #1103: 22112-Remove-code-related-to-HostSystemMenus
by ci-pharo-ci-jenkins2＠inria.fr June 29, 2018

June 29, 2018

There is a new Pharo build available! The status of the build #1103 was: FAILURE. The Pull Request #1518 was integrated: "22112-Remove-code-related-to-HostSystemMenus" Pull request url: https://github.com/pharo-project/pharo/pull/1518 Issue Url: https://pharo.fogbugz.com/f/cases/22112 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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[Pharo 7.0-dev] Build #1102: 21844-Window-fullscreen-size-should-be-dependent-on-world-size
by ci-pharo-ci-jenkins2＠inria.fr June 29, 2018

June 29, 2018

There is a new Pharo build available! The status of the build #1102 was: SUCCESS. The Pull Request #1617 was integrated: "21844-Window-fullscreen-size-should-be-dependent-on-world-size" Pull request url: https://github.com/pharo-project/pharo/pull/1617 Issue Url: https://pharo.fogbugz.com/f/cases/21844 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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[Pharo 7.0-dev] Build #1101: 20579-Ring-Core-Containers-seems-to-be-loaded-twice
by ci-pharo-ci-jenkins2＠inria.fr June 29, 2018

June 29, 2018

There is a new Pharo build available! The status of the build #1101 was: SUCCESS. The Pull Request #1615 was integrated: "20579-Ring-Core-Containers-seems-to-be-loaded-twice" Pull request url: https://github.com/pharo-project/pharo/pull/1615 Issue Url: https://pharo.fogbugz.com/f/cases/20579 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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[Pharo 7.0-dev] Build #1100: 22058-TabMorph-should-handle-wheel-click-and-close-itself-like-in-most-software-as-web-browsers
by ci-pharo-ci-jenkins2＠inria.fr June 29, 2018

June 29, 2018

There is a new Pharo build available! The status of the build #1100 was: SUCCESS. The Pull Request #1482 was integrated: "22058-TabMorph-should-handle-wheel-click-and-close-itself-like-in-most-software-as-web-browsers" Pull request url: https://github.com/pharo-project/pharo/pull/1482 Issue Url: https://pharo.fogbugz.com/f/cases/22058 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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[Pharo 7.0-dev] Build #1099: 22228-Class-copy-and-duplicateClassWithNewName-should-be-correctly-implemented
by ci-pharo-ci-jenkins2＠inria.fr June 29, 2018

June 29, 2018

There is a new Pharo build available! The status of the build #1099 was: SUCCESS. The Pull Request #1613 was integrated: "22228-Class-copy-and-duplicateClassWithNewName-should-be-correctly-implemented" Pull request url: https://github.com/pharo-project/pharo/pull/1613 Issue Url: https://pharo.fogbugz.com/f/cases/22228 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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