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

[Peter Levart]

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