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From "Adrian Nistor (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (COLLECTIONS-413) Performance problem in DualHashBidiMap
Date Thu, 21 Jun 2012 18:39:45 GMT

     [ https://issues.apache.org/jira/browse/COLLECTIONS-413?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Adrian Nistor updated COLLECTIONS-413:
--------------------------------------

    Attachment: Test.java
                patch.diff
    
> Performance problem in DualHashBidiMap
> --------------------------------------
>
>                 Key: COLLECTIONS-413
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-413
>             Project: Commons Collections
>          Issue Type: Bug
>    Affects Versions: 3.2.1
>         Environment: java 1.6.0_24
> Ubuntu 11.10
>            Reporter: Adrian Nistor
>         Attachments: Test.java, patch.diff
>
>
> Hi,
> I am encountering a performance problem in DualHashBidiMap.  It
> appears in version 3.2.1 and also in revision 1352574 (21 June 2012).
> I attached a test that exposes this problem and a patch that fixes it.
> On my machine, for this test, the patch provides a 173X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 5029
> The output for the patched version is:
> Time is 29
> The attached test shows that, for a "DualHashBidiMap bidi" object, the
> following operation is very slow:
> bidi.entrySet().removeAll(toRemove);
> DualHashBidiMap.entrySet() returns a
> "DualHashBidiMap.EntrySet" object, which inherits 
> removeAll(Collection<?> coll) from "DualHashBidiMap.View".  
> As the patch shows, the problem is that
> "DualHashBidiMap.View.removeAll(Collection<?> coll)" performs
> "coll.contains(it.next())" for each element in the View.
> "coll.contains(it.next())" can be very slow, e.g., if "coll" is a
> list.
> The patch avoids this cost by removing from decorate(), which is fast
> because decorate() is a set.
> Is this a bug, or am I misunderstanding something? If so, can you
> please confirm that the patch is correct?
> Thanks,
> Adrian

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