Adrian Nistor created COLLECTIONS-413:
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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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