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[Pharo 7.0-dev] Build #1107: 22235-unsafe-TextMorphForFieldViewminimumExtent
by ci-pharo-ci-jenkins2＠inria.fr July 2, 2018

July 2, 2018

There is a new Pharo build available! The status of the build #1107 was: SUCCESS. The Pull Request #1620 was integrated: "22235-unsafe-TextMorphForFieldViewminimumExtent" Pull request url: https://github.com/pharo-project/pharo/pull/1620 Issue Url: https://pharo.fogbugz.com/f/cases/22235 Build Url: https://ci.inria.fr/pharo-ci-jenkins2/job/Test%20pending%20pull%20request%2…

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Esteban's ChangeLog week of 25 June 2018
by estebanlm＠gmail.com July 2, 2018

July 2, 2018

Hello! This is my weekly ChangeLog, from 25 June 2018 to 1 July 2018. You can see it in a better format by going here: http://log.smallworks.eu/web/search?from=25/6/2018&to=1/7/2018 ChangeLog ========= 27 June 2018: ------------- * I made a [small PR](https://github.com/pharo-project/pharo/pull/1590) to ensure pharo will load correct freetype library when using windows 64bit platform. * I finally was able to build a windows 64bit VM with all dependencies: [https://ci.appveyor.com/project/OpenSmalltalk/vm/build/job/5q50v90myxu4bxxi… This is an important milestone in our Path to have Pharo running in 64bit in all platforms, but sadly this is not finish. While most of the 64bit things I tested are working properly, the cairo plugin (hence Athens) is still not. So I need to spend some more time here, looking at the possible problems :( 25 June 2018: ------------- * I spent some time digging on some issues of Pharo catalog. At the end, it was not very problematic, but at least I took the oportunity to add the repository for Pharo 7.0 :) cheers! Esteban

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Re: [Pharo-dev] [squeak-dev] Why do we have SmallDictionary?
by Chris Muller July 2, 2018

July 2, 2018

>>>> This discussion has limited its context to comparing *in-memory* >>>> Dictionary implementations, where open-addressing has an advantage. >>>> Using Magma reveals another context where chained Dictionary's can have >>>> some advantages: When they're large, persistent, and shared in a >>>> multi-user >>>> system -- e.g., when grow rehashing is not an option. >>> >>> >>> >>> B-trees were designed for that use case. >>> If growing is not an option, then your dictionary's performance will >>> degrade >>> as its size increases, won't it? >> >> >> Yes, but only logarithmically. But I was not making a >> performance-based comparison, only a possibility-based one. > > > Why is it logarithmic? If I have a hash table with an array of size 100, > and I insert 100000 elements into this table, then the best case scenario is > that all the lists are of length 1000. So, the operation cost is not > logarithmic but linear with a small constant: 0.01. Ah, you misunderstood. By "growing is not an option," I meant one would therefore use a _different_ Dictionary implementation, such as one based on a B-Tree, for example. A dictionary whose impelementation organizes or chains its associations into linked lists... - Chris

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Re: [Pharo-dev] [squeak-dev] Why do we have SmallDictionary?
by Chris Muller June 30, 2018

June 30, 2018

>> This discussion has limited its context to comparing *in-memory* >> Dictionary implementations, where open-addressing has an advantage. >> Using Magma reveals another context where chained Dictionary's can have >> some advantages: When they're large, persistent, and shared in a multi-user >> system -- e.g., when grow rehashing is not an option. > > > B-trees were designed for that use case. > If growing is not an option, then your dictionary's performance will degrade > as its size increases, won't it? Yes, but only logarithmically. But I was not making a performance-based comparison, only a possibility-based one. >> Not only do chained Dictionary's make that scenario possible, they improve >> the concurrency -- different users can add/change/remove from the Dictionary >> as long as they occur at different keys. With regular >> Dictionary's, concurrency guarantees a commit conflict. > > If you created a new, larger dictionary on grow and lazily copied the > entries from the smaller to the larger upon access, then I think you could > use open addressing hash tables. That's an interesting idea, but what if it grows beyond "the larger" again while still many entries in the smaller? Add a third which is doubled in size again? That sounds like it starts to intrude into the efficiency of open-addressing (both computation and space), but the idea still sparks some interesting design thoughts in my head.. > Also, I don't see the concurrency issue with open addressing, because as > long as different users modify different chains, the case of concurrency is > the same as what you described, isn't it? Magma has a class called "MagmaPreallocatedDictionary" which does exactly this. It's like a regular Dictionary, except for its internal 'array', it utilizes a MagmaArray, which is just like an Array except large and persistent and can grow in place (so able to maintain its identity). However, this alone was not enough to implement your proposal because of the 'tally'. Clients would each be trying to propose their specific value for that variable = conflict. Thankfully, Magma has yet another special class called MagmaCounter which fits that role beautifully. Designed for multi-user systems, a MagmaCounter provides a concurrent counter. Instances start at a #value of 0, after which any number of sessions may simultaneously increment or decrement (even by more than 1), but no one can actually hard set its value. Best, Chris

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Re: [Pharo-dev] [squeak-dev] Why do we have SmallDictionary?
by Chris Muller June 30, 2018

June 30, 2018

This discussion has limited its context to comparing *in-memory* Dictionary implementations, where open-addressing has an advantage. Using Magma reveals another context where chained Dictionary's can have some advantages: When they're large, persistent, and shared in a multi-user system -- e.g., when grow rehashing is not an option. Not only do chained Dictionary's make that scenario possible, they improve the concurrency -- different users can add/change/remove from the Dictionary as long as they occur at different keys. With regular Dictionary's, concurrency guarantees a commit conflict. - Chris On Fri, Jun 29, 2018 at 2:56 PM, Peter Crowther <peter(a)ozzard.org> wrote: > In an environment with garbage collection, it's worth considering the > overhead of one's representation on the memory allocator and the garbage > collector. Open addressing adds objects - the exact number of these varies > - and hence adds GC overhead (= paying extra cycles for the life of the > dictionary even if it never changes). Each object also has some bytes of > overhead for headers, so chaining becomes less efficient as collisions > occur due to extra object allocations. > > Also, modern processors and memory systems are very good at reading > forward in memory, as there's often a wide memory bus (and sometimes other > optimisations). This means it's often quick to read the next entry as it's > already been pulled in due to adjacency. By contrast, chaining puts > collisions all over memory, reducing adjacency and increasing the bandwidth > required to memory. > > I'm unconvinced that chaining dictionaries are sensible in modern > languages with garbage collection on modern architectures where bandwidth > to memory, and cache space, are both scarce resources. The days of memory > being truly random-access are long gone, and too few programmers realise > the impact that can have. > > Cheers, > > - Peter > > > On 29 June 2018 at 08:27, ClÃ©ment Bera <bera.clement(a)gmail.com> wrote: > >> Hum, about dictionary implementations, I've just found this [1]: >> Open addressing vs. chaining >> *Chaining* *Open addressing* >> *Collision resolution* Using external data structure Using hash table >> itself >> *Memory waste* Pointer size overhead per entry (storing list heads in >> the table) No overhead 1 >> *Performance dependence on table's load factor* Directly proportional Proportional >> to (loadFactor) / (1 - loadFactor) >> *Allow to store more items, than hash table size* Yes No. Moreover, it's >> recommended to keep table's load factor below 0.7 >> *Hash function requirements* Uniform distribution Uniform distribution, >> should avoid clustering >> *Handle removals* Removals are ok Removals clog the hash table with >> "DELETED" entries >> *Implementation* Simple Correct implementation of open addressing based >> hash table is quite tricky1 Hash tables with chaining can work >> efficiently even with load factor more than 1. At the same time, tables >> based on open addressing scheme require load factor not to exceed 0.7 to be >> efficient. Hence, 30% of slots remain empty, which leads to obvious memory >> waste. >> >> Do you guys agree with this? >> >> 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). >> Their chaining implementation does not use balanced binary tree when a >> bucket becomes large like Java's implementation. >> >> 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. >> >> 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/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) >>>>> >>>>> >>>>> >>>> >>>> -- >>>> 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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[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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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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