Counting collector test

CountingTest.java

import java.util.concurrent.TimeUnit;
import java.util.stream.*;
import static java.util.stream.Collectors.*;
import java.util.*;

import org.openjdk.jmh.infra.Blackhole;
import org.openjdk.jmh.annotations.*;
 
@Warmup(iterations = 5, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@BenchmarkMode(Mode.AverageTime)
@OutputTimeUnit(TimeUnit.MICROSECONDS)
@Fork(3)
@State(Scope.Benchmark)
public class CountingTest {
  private List<Integer> input = new Random(1).ints(100000, 0, Integer.MAX_VALUE).boxed().collect(toList());

  @Param({"10", "1000"})
  private int groupCount;

  @Benchmark
  public Map<Integer, Long> countingSeq() {
    return input.stream().collect(groupingBy(i -> i%groupCount, counting()));
  }

  @Benchmark
  public Map<Integer, Long> countingPar() {
    return input.parallelStream().collect(groupingBy(i -> i%groupCount, counting()));
  }

  @Benchmark
  public Map<Integer, Long> summingSeq() {
    return input.stream().collect(groupingBy(i -> i%groupCount, summingLong(t -> 1)));
  }

  @Benchmark
  public Map<Integer, Long> summingPar() {
    return input.parallelStream().collect(groupingBy(i -> i%groupCount, summingLong(t -> 1)));
  }
}

results.txt

# JMH 1.10.3 (released 62 days ago)
# VM version: JDK 1.9.0-ea, VM 1.9.0-ea-b80
# VM invoker: C:\Program Files\Java\jdk1.9.0\bin\java.exe
# VM options: <none>
...
Benchmark                 (groupCount)  Mode  Cnt     Score    Error  Units
CountingTest.countingPar            10  avgt   30   960.248 ± 28.948  us/op
CountingTest.countingPar          1000  avgt   30  2161.591 ± 50.882  us/op
CountingTest.countingSeq            10  avgt   30  3593.732 ± 87.212  us/op
CountingTest.countingSeq          1000  avgt   30  3924.309 ± 58.757  us/op
CountingTest.summingPar             10  avgt   30   686.258 ± 49.852  us/op
CountingTest.summingPar           1000  avgt   30  2158.131 ± 77.969  us/op
CountingTest.summingSeq             10  avgt   30  2686.243 ± 24.384  us/op
CountingTest.summingSeq           1000  avgt   30  3390.783 ± 39.628  us/op