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:
DualHashBidiMap.keySet() returns a "DualHashBidiMap.KeySet" object,
which inherits "retainAll(Collection<?> coll)" from
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
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?