Limit.java

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

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 Limit {
    @Param({"100", "10000", "1000000"})
    private int count;

    @Benchmark
    public void range(Blackhole bh) {
        bh.consume(IntStream.range(0, count).mapToObj(i -> "?").collect(joining(",")));
    }

    @Benchmark
    public void limit(Blackhole bh) {
        bh.consume(Stream.generate(() -> "?").limit(count).collect(joining(",")));
    }

    @Benchmark
    public void rangeParallel(Blackhole bh) {
        bh.consume(IntStream.range(0, count).parallel().mapToObj(i -> "?").collect(joining(",")));
    }

    @Benchmark
    public void rangeUnordered(Blackhole bh) {
        bh.consume(IntStream.range(0, count).parallel().unordered().mapToObj(i -> "?").collect(joining(",")));
    }

    @Benchmark
    public void limitParallel(Blackhole bh) {
        bh.consume(Stream.generate(() -> "?").parallel().limit(count).collect(joining(",")));
    }

    @Benchmark
    public void baseline(Blackhole bh) {
        bh.consume(nCopies("?", ",", count));
    }

    public static String nCopies(String symbol, String delimiter, int count) {
        if(count <= 0) return "";
        char[] result = new char[(symbol.length()+delimiter.length())*count-delimiter.length()];
        fill(result, symbol, delimiter, count);
        return new String(result);
    }

    private static void fill(char[] result, String symbol, String delimiter, int count) {
        if(count == 1) {
            symbol.getChars(0, symbol.length(), result, 0);
            return;
        }
        int half = count/2;
        int filled = (symbol.length()+delimiter.length())*half-delimiter.length();
        if(count % 2 == 0) {
            fill(result, symbol, delimiter, half);
            delimiter.getChars(0, delimiter.length(), result, filled);
            System.arraycopy(result, 0, result, filled+delimiter.length(), filled);
            return;
        }
        fill(result, symbol, delimiter, half);
        int offset = filled;
        delimiter.getChars(0, delimiter.length(), result, offset);
        offset+=delimiter.length();
        symbol.getChars(0, symbol.length(), result, offset);
        offset+=symbol.length();
        delimiter.getChars(0, delimiter.length(), result, offset);
        offset+=delimiter.length();
        System.arraycopy(result, 0, result, offset, filled);
    }
}

results.txt

# JMH 1.9 (released 84 days ago)
# VM invoker: C:\Program Files\Java\jre1.8.0_40\bin\java.exe

Benchmark             (count)  Mode  Cnt      Score      Error  Units
Limit.baseline            100  avgt   30      0.259 ±    0.006  us/op
Limit.baseline          10000  avgt   30     16.664 ±    0.401  us/op
Limit.baseline        1000000  avgt   30   3086.832 ±   84.587  us/op
Limit.limit               100  avgt   30      2.484 ±    0.031  us/op
Limit.limit             10000  avgt   30    233.869 ±    3.366  us/op
Limit.limit           1000000  avgt   30  25773.914 ±  257.290  us/op
Limit.limitParallel       100  avgt   30      9.756 ±    0.265  us/op
Limit.limitParallel     10000  avgt   30    138.175 ±    4.616  us/op
Limit.limitParallel   1000000  avgt   30  15136.506 ±  302.854  us/op
Limit.range               100  avgt   30      2.447 ±    0.023  us/op
Limit.range             10000  avgt   30    243.458 ±    1.805  us/op
Limit.range           1000000  avgt   30  25977.646 ±  379.263  us/op
Limit.rangeParallel       100  avgt   30     10.110 ±    0.527  us/op
Limit.rangeParallel     10000  avgt   30    186.730 ±   28.947  us/op
Limit.rangeParallel   1000000  avgt   30  13758.669 ± 1174.138  us/op
Limit.rangeUnordered      100  avgt   30     11.269 ±    0.752  us/op
Limit.rangeUnordered    10000  avgt   30    160.336 ±    6.875  us/op
Limit.rangeUnordered  1000000  avgt   30  13066.599 ±  271.233  us/op