String.lastIndexOf confused by unpaired trailing surrogate

[Martin Buchholz]

On Tue, Mar 23, 2010 at 13:32, Xueming Shen <Xueming.Shen at sun.com> wrote:
> 6937112: String.lastIndexOf confused by unpaired trailing surrogate
>
> Kinda guess that it might bring us some performance benefit to separate the
> supplementary handling
> code out into its own method (to help the not that smart hotspot:-)?), but
> doubt it is really something
> worth doing. At  least you dont have to have the redundant
> value/offset=this.value/offset.

Yes, this is an "extreme" optimization, but one that is used
pervasively in java.util.concurrent (Doug Lea's influence) and
suitable for performance-critical methods.

It's only downside is the increase in size of source code.
(bytecode is actually smaller)

> Seems like you started to attach the "final" keyword to all
> "constants"...guess it's a hint to help smart
> vm for further optimization. Is the hotspot doing something special in
> simple case like below?

The "final" is there purely for software engineering reasons,
so that people don't make the common mistake of
modifying a field cached in a local, which would have no effect.

Martin

> -Sherman
>
> Martin Buchholz wrote:
>>
>> For a change, here's an actual plain old "incorrect result" bug fix
>> for String.lastIndexOf
>>
>> Sherman, please file a bug and review.
>>
>> http://cr.openjdk.java.net/~martin/webrevs/openjdk7/lastIndexOf/
>>
>> Also includes our usual performance-oriented fiddling.
>>
>> public class LastIndexOf {
>>    public static void main(String[] args) {
>>        int ch = 0x10042;
>>        char[] bug = new char[3];
>>        Character.toChars(ch, bug, 0);
>>        bug[2] = bug[0];
>>        System.out.println(new String(bug).lastIndexOf(ch));
>>        bug[2] = '!';
>>        System.out.println(new String(bug).lastIndexOf(ch));
>>    }
>> }
>> ==> javac -source 1.6 -Xlint:all LastIndexOf.java
>> ==> java -esa -ea LastIndexOf
>> -1
>> 0
>>
>
>