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

Peter Levart peter.levart at gmail.com
Tue Jul 8 21:44:32 UTC 2014

On 07/08/2014 11:39 PM, Ivan Gerasimov wrote:

Might be worth to add modCount++ before this line:

487 table = newTable; 488 return true; Not quite, I think. The map has just been resized, but it's contents has not changed yet logically.

Regards, Peter

On 09.07.2014 0:07, Martin Buchholz wrote:

I updated my webrev and it is again "feature-complete". http://cr.openjdk.java.net/~martin/webrevs/openjdk9/IdentityHashMap-capacity/ <http://cr.openjdk.java.net/%7Emartin/webrevs/openjdk9/IdentityHashMap-capacity/> (old webrev at http://cr.openjdk.java.net/~martin/webrevs/openjdk9/IdentityHashMap-capacity.0/ <http://cr.openjdk.java.net/%7Emartin/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 MAXCAPACITY).

On Tue, Jul 8, 2014 at 8:06 AM, Peter Levart <peter.levart at gmail.com_ _<mailto: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/ <http://cr.openjdk.java.net/%7Eplevart/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/ <http://cr.openjdk.java.net/%7Eplevart/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 tel: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

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