RFR: [6904367]: (coll) IdentityHashMap is resized before exceeding the expected maximum size

[Martin Buchholz]

I updated my webrev and it is again "feature-complete".
http://cr.openjdk.java.net/~martin/webrevs/openjdk9/IdentityHashMap-capacity/
(old webrev at
http://cr.openjdk.java.net/~martin/webrevs/openjdk9/IdentityHashMap-capacity.0/
)

This incorporates Peter's idea of making resize return a boolean, keeps the
map unchanged if resize throws, moves the check for capacity exceeded into
resize, and minimizes bytecode in put().  I'm happy with this (except for
degraded behavior near MAX_CAPACITY).




On Tue, Jul 8, 2014 at 8:06 AM, Peter Levart <peter.levart at gmail.com> wrote:

> On 07/08/2014 03:00 PM, Ivan Gerasimov wrote:
>
>> I took your latest version of the patch and modified it a little:
>>>
>>> http://cr.openjdk.java.net/~plevart/jdk9-dev/IdentityHashMap/webrev.01/
>>>
>>>
>> But isn't it post-insert-resize vs pre-insert-resize problem Doug
>> mentioned above?
>> I've tested a similar fix and it showed slow down of the put() operation.
>>
> Hi Ivan,
>
> Might be that it has to do with # of bytecodes in the method and in-lining
> threshold. I modified it once more, to make put() method as short as
> possible:
>
> http://cr.openjdk.java.net/~plevart/jdk9-dev/IdentityHashMap/webrev.05/
>
> With this, I ran the following JMH benchmark:
>
> @State(Scope.Thread)
> public class IHMBench {
>
>     Map<Object, Object> map = new IdentityHashMap<Object, Object>();
>
>     @Benchmark
>     public void putNewObject(Blackhole bh) {
>         Object o = new Object();
>         bh.consume(map.put(o, o));
>         if (map.size() > 100000) {
>             map = new IdentityHashMap<Object, Object>();
>         }
>     }
> }
>
> I get the following results on my i7/Linux using:
>
> java -Xmx4G -Xms4G -XX:+UseParallelGC -jar benchmarks.jar -f 0 -i 10 -wi 8
> -gc 1 -t 1
>
> Original:
>
> Benchmark                     Mode   Samples        Score  Score error
>  Units
> j.t.IHMBench.putNewObject    thrpt        10 13088296.198 403446.449
>  ops/s
>
> Patched:
>
> Benchmark                     Mode   Samples        Score  Score error
>  Units
> j.t.IHMBench.putNewObject    thrpt        10 13180594.537 282047.154
>  ops/s
>
>
> Can you run your test with webrev.05 and see what you get ?
>
> Regards, Peter
>
>