java_bug

gistfile1.txt

package test;


import org.openjdk.jmh.annotations.BenchmarkType;
import org.openjdk.jmh.annotations.GenerateMicroBenchmark;
import org.openjdk.jmh.annotations.OperationsPerInvocation;
import org.openjdk.jmh.annotations.OutputTimeUnit;

import java.util.concurrent.TimeUnit;

public class TestInlining {
    private static final int ARRAY_LENGTH = 100000;

    public static final class FieldArrayTest {
        public int value;

        void inc() {
            value++;
        }
    }

    public static FieldArrayTest[] testFieldDirect(int incCount) {
        FieldArrayTest[] a = new FieldArrayTest[ARRAY_LENGTH];

        for (int i = 0; i < ARRAY_LENGTH; i++) {
            a[i] = new FieldArrayTest();
        }

        while (incCount-- > 0) {
            for (int i = 0; i < ARRAY_LENGTH; i++) {
                a[i].value++;
            }
        }

        return a;
    }

    public static FieldArrayTest[] testFieldCall(int incCount) {
        FieldArrayTest[] a = new FieldArrayTest[ARRAY_LENGTH];

        for (int i = 0; i < ARRAY_LENGTH; i++) {
            a[i] = new FieldArrayTest();
        }

        while (incCount-- > 0) {
            for (int i = 0; i < ARRAY_LENGTH; i++) {
                a[i].inc();
            }
        }

        return a;
    }

    public static FieldArrayTest[] fill() {
        FieldArrayTest[] a = new FieldArrayTest[ARRAY_LENGTH];
        for (int i = 0; i < ARRAY_LENGTH; i++) {
            a[i] = new FieldArrayTest();
        }

        return a;
    }

    public static Object[] testFieldCall2(FieldArrayTest[] a, int incCount) {
        while (incCount-- > 0) {
            for (int i = 0; i < ARRAY_LENGTH; i++) {
                a[i].inc();
            }
        }

        return a;
    }

    @OutputTimeUnit(TimeUnit.MILLISECONDS)
    @GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
    public Object[] testFieldDirect() {
        return testFieldDirect(1000);
    }

    @OutputTimeUnit(TimeUnit.MILLISECONDS)
    @GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
    public Object[] incrementnFieldCall() {
        return testFieldCall(1000);
    }

    @OutputTimeUnit(TimeUnit.MILLISECONDS)
    @GenerateMicroBenchmark(BenchmarkType.AverageTimePerOp)
    public Object[] incrementnFieldCall2() {
        FieldArrayTest[] a = fill();
        return testFieldCall2(a, 1000);
    }
}

gistfile2.txt

Benchmark                                  Thr    Cnt  Sec    Mean    Mean error          Var    Units
t.g.a.TestInlining.incrementnFieldCall      1     10    1      450.429      6.500       39.999 msec/op
t.g.a.TestInlining.incrementnFieldCall2     1     10    1      110.059        2.148     4.369  msec/op
t.g.a.TestInlining.testFieldDirect          1     10    1      108.779        0.720     0.491  msec/op

Дальнейшие небольшие эксперименты и пачка различных запусков показало, 
что даже t.g.a.TestInlining.incrementnFieldCall каждый 9-10 запуск может выдавать скорость около 110 msec/op.

https://github.com/shipilev/benchmarks-scratch/blob/master/src/main/java/org/sample/TestInlining.java

Benchmark                                 Mode Thr    Cnt  Sec         Mean   Mean error    Units
o.s.TestInlining.incrementnFieldCall      avgt   1      5    1      164.252        3.330  msec/op
o.s.TestInlining.incrementnFieldCall2     avgt   1      5    1      164.254        4.717  msec/op
o.s.TestInlining.testFieldDirect          avgt   1      5    1      165.744        5.366  msec/op

The same, with -f 10:

Benchmark                                 Mode Thr    Cnt  Sec         Mean   Mean error    Units
o.s.TestInlining.incrementnFieldCall      avgt   1     50    1      619.174       57.914  msec/op
o.s.TestInlining.incrementnFieldCall2     avgt   1     50    1      166.097        0.952  msec/op
o.s.TestInlining.testFieldDirect          avgt   1     50    1      166.813        1.298  msec/op