LinkedList facelift

[Rémi Forax]

Le 03/11/2009 03:29, Martin Buchholz a écrit :
> I would like to contribute an improvement to LinkedList
>
> webrev:
> http://cr.openjdk.java.net/~martin/webrevs/openjdk7/LinkedList/
>
> Josh, Bill and I have discussed this offline,
> and they have given their blessing.
> (i.e. I am not asking for reviewers)
>
> I apologize for this - there are so many more important things to work on,
> and no one is really using LinkedList
> in performance-sensitive production code, eh?
>
> Chris, could you file a bug?
>
> Synopsis:  LinkedList facelift
>
> Description:
> - A list of size N should create only N+1 objects, not N+2.
> - Use of null as sentinel value instead of a sentinel (Null Object)
>    is slightly less convenient, but is measurably faster, since hotspot
>    has to insert null checks (with NPE throws) anyways.
> - generify
> - warning removal
> - gratuitous tests added.
> - cosmetic doc improvements
> - the original motivation for this was to have a O(1) clear,
>    but we eventually decided against that
>    - but we documented our decision.
>
> Below is a stupid microbenchmark demonstrating app. a factor of 2 improvement in
> "throughput", and a 50% increase in memory footprint.
>
> public class LinkedListBench {
>     public static void main(String[] args) {
>         LinkedList spine = new LinkedList();
>         long i = 0;
>         long t0 = System.nanoTime();
>         try {
>             for (i = 0; ; i++) {
>                 spine.add(new LinkedList());
>             }
>         } catch (OutOfMemoryError e) {
>             spine.clear();
>             System.out.printf("allocated = %d%n", i);
>             System.out.printf("ns/object = %d%n", (System.nanoTime()-t0)/i);
>         }
>     }
> }
>
>
> Thanks,
>
> Martin
>    

Hi Martin,
Your patch can break backward compat.

add(E) now delegates to a public method (an overridable one)
(addLast). So If I have a class that inherits from LinkedList
and overrides addLast() the current semantics of add(E) is not altered,
with your patch, add(E) semantics is also changed.

I think the code of addLast() should be in a private method and
addLast() and add(E) delegate to it.

Rémi