SpliteratorBenchmark.java

SpliteratorBenchmark.java

public static class SpliteratorBenchmark {
  static double sink;

  public static void main(String[] args) throws IOException {
    final Path inputPath = createInput();
    for (int i = 0; i < 3; i++) {
      System.out.println("Start processing JDK stream");
      measureProcessing(Files.lines(inputPath));
      System.out.println("Start processing fixed-batch stream");
      measureProcessing(withBatchSize(Files.lines(inputPath), 500));
    }
  }

  private static Stream<String> withBatchSize(Stream<String> in, int batchSize) {
    return stream(batchedSpliterator(in.iterator(), batchSize), true);
  }

  private static Spliterator<String> batchedSpliterator(Iterator<String> toWrap, int batchSize) {
    PagingIterable<String> iterable = new MockPagingIterable<>(toWrap);
    return new PagingIterableSpliterator<>(iterable, batchSize);
  }

  private static void measureProcessing(Stream<String> input) throws IOException {
    final long start = System.nanoTime();
    try (Stream<String> lines = input) {
      final long totalTime = lines.parallel().mapToLong(SpliteratorBenchmark::processLine).sum();
      final double cpuTime = totalTime, realTime = System.nanoTime() - start;
      final int cores = Runtime.getRuntime().availableProcessors();
      System.out.println("          Cores: " + cores);
      System.out.format("       CPU time: %.2f s\n", cpuTime / SECONDS.toNanos(1));
      System.out.format("      Real time: %.2f s\n", realTime / SECONDS.toNanos(1));
      System.out.format("CPU utilization: %.2f%%\n\n", 100.0 * cpuTime / realTime / cores);
    }
  }

  private static long processLine(String line) {
    final long localStart = System.nanoTime();
    double d = 0;
    for (int i = 0; i < line.length(); i++)
      for (int j = 0; j < line.length(); j++)
        d += Math.pow(line.charAt(i), line.charAt(j) / 32.0);
    sink += d;
    return System.nanoTime() - localStart;
  }

  private static Path createInput() throws IOException {
    final Path inputPath = Paths.get("input.txt");
    try (PrintWriter w = new PrintWriter(Files.newBufferedWriter(inputPath))) {
      for (int i = 0; i < 20_000; i++) {
        final String text = String.valueOf(System.nanoTime());
        for (int j = 0; j < 15; j++) w.print(text);
        w.println();
      }
    }
    return inputPath;
  }
}