[COLLECTIONS-410] SetUniqueList.addAll() is very slow

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

Environment

java 1.6.0_24
Ubuntu 11.10

• Assignee: Unassigned
• Reporter: Adrian Nistor
• Created: 19/Jun/12 20:37
• Updated: 09/Nov/14 14:31
• Resolved: 20/Jun/12 18:04

Description

Hi,

I am encountering a performance problem in SetUniqueList.addAll(). It
appears in revision 1351837 (19 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 540X speedup.

To run the test, just do:

$ java Test

The output for the un-patched version is:
Time is 2706

The output for the patched version is:
Time is 5

As the patch shows, the problem is that
SetUniqueList.addAll(int index, Collection<? extends E> coll)
performs:
"add(index, e)" for each element in "coll". This is very expensive,
because each "add(index, e)" performs a
LinkedList.add(int index, E element), which requires traversing the
LinkedList to find the index.

The patched version avoids this cost by inserting all the elements at
once, thus performing only one insert.

Is this a bug? If so, can you please confirm that the patch is
correct?

Thanks,

Adrian