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

[Ivan Gerasimov]

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

 487         table = newTable;
 488         return true;


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 MAX_CAPACITY).

On Tue, Jul 8, 2014 at 8:06 AM, Peter Levart <peter.lev...@gmail.com <mailto:peter.lev...@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