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From "Adrian Nistor (JIRA)" <j...@apache.org>
Subject [jira] [Created] (COLLECTIONS-407) ListOrderedSet.removeAll() is slow
Date Fri, 01 Jun 2012 17:56:23 GMT
Adrian Nistor created COLLECTIONS-407:
-----------------------------------------

             Summary: 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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