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From "Thomas Neidhart (JIRA)" <j...@apache.org>
Subject [jira] [Resolved] (COLLECTIONS-410) SetUniqueList.addAll() is very slow
Date Wed, 20 Jun 2012 18:04:45 GMT

     [ https://issues.apache.org/jira/browse/COLLECTIONS-410?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Thomas Neidhart resolved COLLECTIONS-410.
-----------------------------------------

       Resolution: Fixed
    Fix Version/s: 4.0

Applied patch in r1352243.

Thanks for reporting!
                
> SetUniqueList.addAll() is very slow
> -----------------------------------
>
>                 Key: COLLECTIONS-410
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-410
>             Project: Commons Collections
>          Issue Type: Bug
>         Environment: java 1.6.0_24
> Ubuntu 11.10
>            Reporter: Adrian Nistor
>             Fix For: 4.0
>
>         Attachments: Test.java, patch.diff
>
>
> Hi,
> I am encountering a performance problem in SetUniqueList.addAll().  It
> appears in revision 1351837 (19 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 540X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 2706
> The output for the patched version is:
> Time is 5
> As the patch shows, the problem is that
> SetUniqueList.addAll(int index, Collection<? extends E> coll)
> performs:
> "add(index, e)" for each element in "coll". This is very expensive, 
> because each "add(index, e)" performs a 
> LinkedList.add(int index, E element), which requires traversing the 
> LinkedList to find the index.
> The patched version avoids this cost by inserting all the elements at
> once, thus performing only one insert.
> Is this a bug? If so, can you please confirm that the patch is
> correct?
> Thanks,
> Adrian

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