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:
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
The patch avoids this cost by using remove(Object obj) (defined in
"EntrySet<K, V>", "KeySet<K>", and "Values<V>"), which is fast because
it uses only operations on sets.
Is this a bug, or am I misunderstanding something? If so, can you
please confirm that the patch is correct?