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https://issues.apache.org/jira/browse/COLLECTIONS-419?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Thomas Neidhart resolved COLLECTIONS-419.
-----------------------------------------
Resolution: Fixed
Added clarifying javadoc to the method in r1470170, similar to the one applied
for COLLECTIONS-417.
Thanks for the report.
> 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
> Priority: Minor
> Fix For: 4.0
>
> 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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