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From "Adrian Nistor (JIRA)" <j...@apache.org>
Subject [jira] [Created] (COLLECTIONS-413) Performance problem in DualHashBidiMap
Date Thu, 21 Jun 2012 18:39:44 GMT
Adrian Nistor created COLLECTIONS-413:
-----------------------------------------

             Summary: 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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