ArrayCopy.java

package com.dbobrov.benchmark;

import org.openjdk.jmh.annotations.*;

import java.util.concurrent.TimeUnit;

@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@State
public class ArrayCopy {
    private long[] arr;
    private int[] iArr;
    private Long[] refArr;

    @Setup
    public void setup() {
        arr = new long[100000];
        for (int i = 0; i < 100000; i++)
            arr[i] = i;

        refArr = new Long[100000];
        for (int i = 0; i < 100000; i++)
            refArr[i] = (long)i;

        iArr = new int[100000];
        for (int i = 0; i < 100000; i++)
            iArr[i] = i;
    }

    @GenerateMicroBenchmark
    public long[] system() {
        long[] res = new long[arr.length];
        System.arraycopy(arr, 0, res, 0, arr.length);
        return res;
    }

    @GenerateMicroBenchmark
    public long[] loop() {
        long[] res = new long[arr.length];
        for (int i = 0; i < arr.length; i++) {
            res[i] = arr[i];
        }
        return res;
    }

    @GenerateMicroBenchmark
    public int[] systemI() {
        int[] res = new int[iArr.length];
        System.arraycopy(iArr, 0, res, 0, iArr.length);
        return res;
    }

    @GenerateMicroBenchmark
    public int[] loopI() {
        int[] res = new int[iArr.length];
        for (int i = 0; i < iArr.length; i++) {
            res[i] = iArr[i];
        }
        return res;
    }

    @GenerateMicroBenchmark
    public Long[] systemRef() {
        Long[] res = new Long[refArr.length];
        System.arraycopy(refArr, 0, res, 0, refArr.length);
        return res;
    }

    @GenerateMicroBenchmark
    public Long[] loopRef() {
        Long[] res = new Long[refArr.length];
        for (int i = 0; i < refArr.length; i++) {
            res[i] = refArr[i];
        }
        return res;
    }
}

Results.txt

java -XX:+UseCompressedOops -jar target/microbenchmarks.jar ".*ArrayCopy.*" -i 5 -wi 20 -f 2
Benchmark                     Mode Thr     Count  Sec         Mean   Mean error    Units
c.d.b.ArrayCopy.loop          avgt   1        10    1      260.713        7.256    us/op
c.d.b.ArrayCopy.loopI         avgt   1        10    1      133.645       11.282    us/op
c.d.b.ArrayCopy.loopRef       avgt   1        10    1      224.961       18.164    us/op
c.d.b.ArrayCopy.system        avgt   1        20    1      179.633        1.203    us/op  // runned separately with 40 warmup iterations
c.d.b.ArrayCopy.systemI       avgt   1        10    1       91.585        6.170    us/op
c.d.b.ArrayCopy.systemRef     avgt   1        10    1      127.822        6.393    us/op

java -XX:-UseCompressedOops -jar target/microbenchmarks.jar ".*ArrayCopy.*" -i 5 -wi 20 -f 2
Benchmark                     Mode Thr     Count  Sec         Mean   Mean error    Units
c.d.b.ArrayCopy.loop          avgt   1        10    1      262.489        8.358    us/op
c.d.b.ArrayCopy.loopI         avgt   1        10    1      129.528        4.491    us/op
c.d.b.ArrayCopy.loopRef       avgt   1        10    1      341.100        4.476    us/op
c.d.b.ArrayCopy.system        avgt   1        20    1      179.255        2.727    us/op  // runned separately with 40 warmup iterations
c.d.b.ArrayCopy.systemI       avgt   1        10    1       88.850        1.932    us/op
c.d.b.ArrayCopy.systemRef     avgt   1        10    1      256.901        1.876    us/op

System.arraycopy for long[] warmup

# Warmup Iteration   1: 309.028 us/op
# Warmup Iteration   2: 221.333 us/op
# Warmup Iteration   3: 178.869 us/op
# Warmup Iteration   4: 179.689 us/op
# Warmup Iteration   5: 182.037 us/op
# Warmup Iteration   6: 180.258 us/op
# Warmup Iteration   7: 179.259 us/op
# Warmup Iteration   8: 179.932 us/op
# Warmup Iteration   9: 180.366 us/op
# Warmup Iteration  10: 180.112 us/op
# Warmup Iteration  11: 178.558 us/op
# Warmup Iteration  12: 199.839 us/op
# Warmup Iteration  13: 247.690 us/op
# Warmup Iteration  14: 251.402 us/op
# Warmup Iteration  15: 249.377 us/op
# Warmup Iteration  16: 250.163 us/op
# Warmup Iteration  17: 249.931 us/op
# Warmup Iteration  18: 251.042 us/op
# Warmup Iteration  19: 252.276 us/op
# Warmup Iteration  20: 249.913 us/op
# Warmup Iteration  21: 249.253 us/op
# Warmup Iteration  22: 250.548 us/op
# Warmup Iteration  23: 249.159 us/op
# Warmup Iteration  24: 225.688 us/op
# Warmup Iteration  25: 184.037 us/op
# Warmup Iteration  26: 178.373 us/op
# Warmup Iteration  27: 178.506 us/op
# Warmup Iteration  28: 178.471 us/op
# Warmup Iteration  29: 180.717 us/op
# Warmup Iteration  30: 179.385 us/op
# Warmup Iteration  31: 177.574 us/op
# Warmup Iteration  32: 177.429 us/op
# Warmup Iteration  33: 178.025 us/op
# Warmup Iteration  34: 177.862 us/op
# Warmup Iteration  35: 179.531 us/op
# Warmup Iteration  36: 178.716 us/op
# Warmup Iteration  37: 178.471 us/op
# Warmup Iteration  38: 178.945 us/op
# Warmup Iteration  39: 179.210 us/op
# Warmup Iteration  40: 180.171 us/op