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Date: Tue, 19 Jun 2012 16:21:43 +0000 (UTC)
From: "Thomas Neidhart (JIRA)" <jira@apache.org>
To: issues@commons.apache.org
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Subject: [jira] [Commented] (COLLECTIONS-407) ListOrderedSet.removeAll() is
 slow
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    [ https://issues.apache.org/jira/browse/COLLECTIONS-407?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13396899#comment-13396899 ] 

Thomas Neidhart commented on COLLECTIONS-407:
---------------------------------------------

You are right, in fact other methods (in ListOrderedSet, e.g. retainAll) already use similar logic as proposed in your patch, so I guess it is safe to do it also for the remove method.
                
> ListOrderedSet.removeAll() is slow
> ----------------------------------
>
>                 Key: COLLECTIONS-407
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-407
>             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 ListOrderedSet.removeAll().
> It appears in version 3.2.1 and also in revision 1344775 (31 May
> 2012).  I have 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 317X speedup.
> To run the test, just do:
> $ java Test
> The output for the un-patched version is:
> Time is 3812
> The output for the patched version is:
> Time is 12
> As the patch shows, the problem is in 
> ListOrderedSet.remove(Object object).  The code for this method is:
> boolean result = collection.remove(object);
> setOrder.remove(object);
> return result;
> The patch changes it to :
> boolean result = collection.remove(object);
> if (result) setOrder.remove(object);
> return result;
> The "setOrder.remove(object)" is not necessary if 
> "collection.remove(object)" did not find the object.
> This small change speeds up
> ListOrderedSet.ListOrderedSet.removeAll(Collection<?> coll) because
> ListOrderedSet.ListOrderedSet.removeAll(Collection<?> coll) iterates
> over all the elements in "coll" and calls 
> ListOrderedSet.remove(Object object).  So the un-patched code has
> quadratic complexity, while the patched code has linear complexity.
> Is this truly a bug, or am I missing something here?  If so, can you
> please confirm if the patch is correct?
> Thanks,
> Adrian

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