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From "Thomas Neidhart (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (COLLECTIONS-419) Performance problem in AbstractDualBidiMap
Date Thu, 07 Feb 2013 17:53:13 GMT

     [ https://issues.apache.org/jira/browse/COLLECTIONS-419?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Thomas Neidhart updated COLLECTIONS-419:
----------------------------------------

    Issue Type: Improvement  (was: Bug)
    
> Performance problem in AbstractDualBidiMap
> ------------------------------------------
>
>                 Key: COLLECTIONS-419
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-419
>             Project: Commons Collections
>          Issue Type: Improvement
>    Affects Versions: 3.2.1
>         Environment: java 1.6.0_24
> Ubuntu 11.10
>            Reporter: Adrian Nistor
>         Attachments: patch.diff, Test.java
>
>
> Hi,
> I am encountering a performance problem in AbstractDualBidiMap.  It
> appears in version 3.2.1 and also in revision 1355448.  I attached a
> test that exposes this problem and a one-line patch that fixes it.  On
> my machine, for this test, the patch provides a 130X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 5460
> The output for the patched version is:
> Time is 42
> The attached test shows that, for a "DualHashBidiMap bidi" object, the
> following operation is very slow:
> bidi.keySet().retainAll(toRetain)
> DualHashBidiMap.keySet() returns a "DualHashBidiMap.KeySet" object,
> which inherits "retainAll(Collection<?> coll)" from
> "AbstractDualBidiMap.View". Similarly,
> bidi.values().retainAll(toRetain)
> bidi.entrySet().retainAll(toRetain)
> are also slow.  This happens for both DualHashBidiMap and
> DualTreeBidiMap, which extend AbstractDualBidiMap.
> As the patch shows, the problem is that
> "AbstractDualBidiMap.View.retainAll(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 one-line patch I attached puts the elements of "coll" in a HashSet
> (which has very fast "contains()"), if "coll" is not already a set:
> "if (!(coll instanceof Set<?>)) coll = new java.util.HashSet<Object>(coll);"
> Is this a bug, or am I misunderstanding the intended behavior? If so,
> can you please confirm that the patch is correct?
> Thanks,
> Adrian

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