RFR: 8312164: Refactor Arrays.hashCode for long, boolean, double, float, and Object arrays [v3]

[Glavo]

On Wed, 19 Jul 2023 13:14:23 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> Please review this PR to refactor Arrays.hashCode for long[], boolean[], and Object[]. I've been told elsewhere that it shouldn't have significant performance implications.
>
> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix hashCode(float[])

I ran a JMH benchmark for this PR:


@Warmup(iterations = 5, time = 3)
@Measurement(iterations = 5, time = 2)
@Fork(value = 1, jvmArgsAppend = {"-XX:+UseG1GC", "-Xms8g", "-Xmx8g"})
@BenchmarkMode(Mode.Throughput)
@OutputTimeUnit(TimeUnit.MILLISECONDS)
@State(Scope.Benchmark)
public class HashCode {
    @Param({"1", "10", "100", "10000"})
    private int size;

    private long[] longs;
    private boolean[] booleans;
    private float[] floats;
    private double[] doubles;
    private Object[] objects;

    @Setup
    public void setup() {
        longs = new long[size];
        booleans = new boolean[size];
        floats = new float[size];
        doubles = new double[size];
        objects = new Object[size];

        Random rnd = new Random(0);
        for (int i = 0; i < size; i++) {
            long next = rnd.nextLong();

            longs[i] = next;
            booleans[i] = next % 2 == 0;
            floats[i] = Float.intBitsToFloat((int) next);
            doubles[i] = Double.longBitsToDouble(next);
            objects[i] = (int) next;
        }
    }

    @Benchmark
    public int longs() {
        return Arrays.hashCode(longs);
    }

    @Benchmark
    public int booleans() {
        return Arrays.hashCode(booleans);
    }

    @Benchmark
    public int floats() {
        return Arrays.hashCode(floats);
    }

    @Benchmark
    public int doubles() {
        return Arrays.hashCode(doubles);
    }

    @Benchmark
    public int objects() {
        return Arrays.hashCode(objects);
    }
}



Result:

                                                 (This PR)                        (Baseline)   

Benchmark          (size)   Mode  Cnt       Score       Error   Units         Score       Error   Units
HashCode.booleans       1  thrpt    5  472358.594 ±  5037.260  ops/ms    473356.084 ±  1780.600  ops/ms
HashCode.booleans      10  thrpt    5  118457.276 ±   848.886  ops/ms    118470.818 ±   342.023  ops/ms
HashCode.booleans     100  thrpt    5   13140.346 ±    46.869  ops/ms     13153.643 ±     1.226  ops/ms
HashCode.booleans   10000  thrpt    5     133.090 ±     0.027  ops/ms       133.041 ±     0.032  ops/ms
HashCode.doubles        1  thrpt    5  438869.947 ±  1806.730  ops/ms    441611.989 ±   692.622  ops/ms
HashCode.doubles       10  thrpt    5   76418.134 ±    42.834  ops/ms     76432.141 ±   368.953  ops/ms
HashCode.doubles      100  thrpt    5    7364.920 ±     6.941  ops/ms      7339.776 ±    28.448  ops/ms
HashCode.doubles    10000  thrpt    5      76.689 ±     0.037  ops/ms        76.787 ±     0.188  ops/ms
HashCode.floats         1  thrpt    5  443741.068 ±  1773.736  ops/ms    444085.364 ±   557.545  ops/ms
HashCode.floats        10  thrpt    5   86047.878 ±   306.709  ops/ms     86306.681 ±   908.752  ops/ms
HashCode.floats       100  thrpt    5    8263.785 ±    37.091  ops/ms      8254.055 ±     3.427  ops/ms
HashCode.floats     10000  thrpt    5      86.146 ±     0.018  ops/ms        86.121 ±     0.022  ops/ms
HashCode.longs          1  thrpt    5  462198.590 ± 27224.002  ops/ms    460673.957 ± 26979.630  ops/ms
HashCode.longs         10  thrpt    5  124744.207 ±   262.268  ops/ms    130367.753 ±   257.766  ops/ms
HashCode.longs        100  thrpt    5   13552.607 ±     2.545  ops/ms     13454.362 ±     8.991  ops/ms
HashCode.longs      10000  thrpt    5     133.122 ±     0.038  ops/ms       133.114 ±     0.016  ops/ms
HashCode.objects        1  thrpt    5  230303.967 ±   919.637  ops/ms    647597.213 ±  2652.002  ops/ms
HashCode.objects       10  thrpt    5   25724.486 ±   111.422  ops/ms    121222.501 ±   270.073  ops/ms
HashCode.objects      100  thrpt    5    2497.018 ±     6.201  ops/ms     11889.717 ±   264.730  ops/ms
HashCode.objects    10000  thrpt    5      27.673 ±     0.012  ops/ms       130.903 ±     0.714  ops/ms


I think there is a performance issue with this PR. For object arrays, the performance is reduced by about 80%.

(I got the result reversed in a previous comment, so I hid it.)

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PR Review: https://git.openjdk.org/jdk/pull/14900#pullrequestreview-1538245804