[COLLECTIONS-407] ListOrderedSet.removeAll() is slow

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.2.1
• Fix Version/s: 4.0-alpha1, 4.0

Environment

java 1.6.0_24
Ubuntu 11.10

• Assignee: Unassigned
• Reporter: Adrian Nistor
• Created: 01/Jun/12 17:55
• Updated: 09/Nov/14 14:31
• Resolved: 19/Jun/12 19:00

Description

Hi,

I am encountering a performance problem in ListOrderedSet.removeAll().
It appears in version 3.2.1 and also in revision 1344775 (31 May
2012). I have 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 317X speedup.

To run the test, just do:

$ java Test

The output for the un-patched version is:
Time is 3812

The output for the patched version is:
Time is 12

As the patch shows, the problem is in
ListOrderedSet.remove(Object object). The code for this method is:

boolean result = collection.remove(object);
setOrder.remove(object);
return result;

The patch changes it to :

boolean result = collection.remove(object);
if (result) setOrder.remove(object);
return result;

The "setOrder.remove(object)" is not necessary if
"collection.remove(object)" did not find the object.

This small change speeds up
ListOrderedSet.ListOrderedSet.removeAll(Collection<?> coll) because
ListOrderedSet.ListOrderedSet.removeAll(Collection<?> coll) iterates
over all the elements in "coll" and calls
ListOrderedSet.remove(Object object). So the un-patched code has
quadratic complexity, while the patched code has linear complexity.

Is this truly a bug, or am I missing something here? If so, can you
please confirm if the patch is correct?

Thanks,

Adrian

Issue Links

• is related to: COLLECTIONS-408 performance problem in SetUniqueList.removeAll()
• relates to: COLLECTIONS-409 ListOrderedSet.addAll() is very slow