Adrian Nistor created COLLECTIONS-419:
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Summary: Performance problem in AbstractDualBidiMap
Key: COLLECTIONS-419
URL: https://issues.apache.org/jira/browse/COLLECTIONS-419
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 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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