Hi Victor, Thanks for the clarification/verification. Would you like me to open an issue on github for akka project?
cheers /dom On Tuesday, 14 January 2014 10:26:25 UTC, √ wrote: > > Hi Dominic, > > you are absolutely right, looks like we need to clear it before removing > it. > > Cheers, > √ > > > On Tue, Jan 14, 2014 at 11:21 AM, Dominic Tootell > <dominic...@gmail.com<javascript:> > > wrote: > >> Hi Victor >> >> Thanks for the message, >> I mean the other public def remove, that is just removing the entire set >> from the map: >> >> https://github.com/akka/akka/blob/master/akka-actor/src/ >> main/scala/akka/util/Index.scala#L137<https://github.com/akka/akka/blob/master/akka-actor/src/main/scala/akka/util/Index.scala#L124> >> >> I wrote an example of the use of the above def remove(K), used in >> conjunction with put(K,V), which shows the issue: >> >> - >> https://github.com/tootedom/akka-cmm/blob/master/src/main/scala/org/greencheek/akka/cmm/MainUnsynchronizedAkkaCmm.scala >> >> there's a subsequent implementation that just does .synchronized on the >> map >> >> - >> https://github.com/tootedom/akka-cmm/blob/master/src/main/scala/org/greencheek/akka/cmm/MainSynchronizedRemoveAndAdd.scala >> >> The test case just loops 1 to 1000 in two threads.. one puts, the other >> removes. The removes just adds up the number of elements in the set >> returned by the remove(K). A Crude example for sure, but it seemed to demo >> this issue on my macbook. >> >> >> Cheers >> /dom >> >> >> On Tuesday, 14 January 2014 10:12:17 UTC, √ wrote: >> >>> Hi Dominic, >>> >>> thanks for spending time to shoot holes in Index! >>> >>> >>> On Tue, Jan 14, 2014 at 8:27 AM, Dominic Tootell >>> <dominic...@gmail.com>wrote: >>> >>>> Hi there, >>>> >>>> Apologies if this question has been asked elsewhere, and if I'm not >>>> correct in my thought process. >>>> I was looking around for a ConcurrentMultiMap implementation and came >>>> across the one in akka after searching. >>>> >>>> The implementation I'm referencing is the following: >>>> >>>> - https://github.com/akka/akka/blob/master/akka-actor/src/ >>>> main/scala/akka/util/Index.scala >>>> >>>> The use case I was looking at is as follows: >>>> >>>> (a) If the existing key (K) was present in the map, the (V) would be >>>> put onto the existing Set of V's associated with the K. >>>> (b) If the K did not exist in the map a new Set with V as the initial >>>> value would be added, to the map associated with K. >>>> >>>> The .put(K,V) would work concurrently with remove(K), such that V, >>>> would either be in the >>>> Set removed by remove(K) (when that method completes); or would be >>>> added to the map as (b), >>>> if remove(K) completed before the put(K,V) did. >>>> >>>> Looking at the source of Index.scala, it looks as thought the above use >>>> case is not satisfied by the implementation. >>>> Such that there could be (forgive me if I'm wrong here), a slight >>>> possibility for the put(K,V) >>>> to neither be added to the map (in an existing or new Set), or be in >>>> the Set removed by remove(K) >>>> (when that method completes). This could be a completely valid for >>>> it's use case it has been developed for. >>>> >>>> For example: >>>> >>>> Say Thread t1 runs in put(K,Vy) up to line 52 (completes it) and >>>> returns a Set such that oldSet is a Set of one V >>>> (i.e. it is running per the use case in the comment "// Parry for two >>>> simultaneous putIfAbsent(id,newSet)") >>>> >>>> Say Thread t1 is ctx switched (unscheduled by the OS) and Thread t2 is >>>> scheduled and calls remove(K), which completes, >>>> and t2 does what it needs on the returned Set (the Vy from t1.put(K,Vy) >>>> is not in the Set processed by t2). >>>> >>>> Thread t1 is once again scheduled and runs. The oldSet is niether >>>> null, or empty. As a result the set is appended >>>> to with Vy, and the method returns. However, the Set Vy was appended >>>> to is >>>> neither in the Map (associated with K) due to t2's remove operation, or >>>> was it in the Set when t2 removed it. >>>> As a result the value, from the put(K,V) goes missing. >>>> >>> >>> Check def remove, it only removes Sets from the Map if they are empty, >>> and if it is empty: >>> https://github.com/akka/akka/blob/master/akka-actor/src/ >>> main/scala/akka/util/Index.scala#L124 >>> >>> And if def put sees an empty set, it will retry: >>> https://github.com/akka/akka/blob/master/akka-actor/src/ >>> main/scala/akka/util/Index.scala#L55 >>> >>> If you add a sleep after putIfAbsent, can you provoke a bug? >>> >>> Cheers, >>> √ >>> >>> >>>> The documentation http://doc.akka.io/api/akka/2.2.3/#akka.util. >>>> ConcurrentMultiMap >>>> specifies that the Add/remove is serialized over the specified key; >>>> which seems to indicate that >>>> add/remove shouldn't cause a race condition. However, it depends on how >>>> that is in interpreted. >>>> Therefore, I'm unsure if add/remove for the MultiMap implementation >>>> were meant to be synchronized with each other >>>> or not. >>>> >>>> A simple test case of the above can be found here: >>>> https://github.com/tootedom/akka-cmm >>>> >>>> I was just wondering if this Race condition in the remove(K), and >>>> put(K,V); is expected by design >>>> or if perhaps it a valid issue in the implementation, and as a result >>>> an issue for akka itself, for >>>> the LookupClassification trait in https://github.com/akka/akka/ >>>> blob/master/akka-actor/src/main/scala/akka/event/EventBus.scala >>>> >>>> Apologies if the above doesn't make sense. >>>> >>>> thanks >>>> /dom >>>> >>>> -- >>>> >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>> >>>>>>>>>> Check the FAQ: http://akka.io/faq/ >>>> >>>>>>>>>> Search the archives: https://groups.google.com/ >>>> group/akka-user >>>> --- >>>> You received this message because you are subscribed to the Google >>>> Groups "Akka User List" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to akka-user+...@googlegroups.com. >>>> To post to this group, send email to akka...@googlegroups.com. >>>> >>>> Visit this group at http://groups.google.com/group/akka-user. >>>> For more options, visit https://groups.google.com/groups/opt_out. >>>> >>> >>> >>> >>> -- >>> Cheers, >>> √ >>> >>> * Viktor Klang* >>> *Director of Engineering* >>> Typesafe <http://www.typesafe.com/> >>> >>> Twitter: @viktorklang >>> >> -- >> >>>>>>>>>> Read the docs: http://akka.io/docs/ >> >>>>>>>>>> Check the FAQ: http://akka.io/faq/ >> >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user >> --- >> You received this message because you are subscribed to the Google Groups >> "Akka User List" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to akka-user+...@googlegroups.com <javascript:>. >> To post to this group, send email to akka...@googlegroups.com<javascript:> >> . >> Visit this group at http://groups.google.com/group/akka-user. >> For more options, visit https://groups.google.com/groups/opt_out. >> > > > > -- > Cheers, > √ > > * Viktor Klang* > *Director of Engineering* > Typesafe <http://www.typesafe.com/> > > Twitter: @viktorklang > -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: http://akka.io/faq/ >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. 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