code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.concurrent.Exchanger;
  
  /*
   * Written by Doug Lea with assistance from members of JCP JSR-166
   * Expert Group and released to the public domain, as explained at
   * http://creativecommons.org/licenses/publicdomain
   */
  
  /*
   * @test
   * @bug 4486658
   * @compile -source 1.5 ExchangeLoops.java
   * @run main/timeout=720 ExchangeLoops
   * @summary checks to make sure a pipeline of exchangers passes data.
   */
  
  import java.util.concurrent.*;
  
  public class ExchangeLoops {
      static final ExecutorService pool = Executors.newCachedThreadPool();
      static boolean print = false;
  
      static class Int {
          public int value;
          Int(int i) { value = i; }
      }
  
  
      public static void main(String[] args) throws Exception {
          int maxStages = 5;
          int iters = 10000;
  
          if (args.length > 0)
              maxStages = Integer.parseInt(args[0]);
  
          print = false;
          System.out.println("Warmup...");
          oneRun(2, 100000);
          print = true;
  
          for (int i = 2; i <= maxStages; i += (i+1) >>> 1) {
              System.out.print("Threads: " + i + "\t: ");
              oneRun(i, iters);
          }
          pool.shutdown();
          if (! pool.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS))
              throw new Error();
     }
  
      static class Stage implements Runnable {
          final int iters;
          final Exchanger<Int> left;
          final Exchanger<Int> right;
          final CyclicBarrier barrier;
          volatile int result;
          Stage (Exchanger<Int> left,
                 Exchanger<Int> right,
                 CyclicBarrier b, int iters) {
              this.left = left;
              this.right = right;
              barrier = b;
              this.iters = iters;
          }
  
          public void run() {
              try {
                  barrier.await();
                  Int item = new Int(hashCode());
                  for (int i = 0; i < iters; ++i) {
                      if (left != null) {
                          item.value = LoopHelpers.compute1(item.value);
                          Int other = left.exchange(item);
                          if (other == item || other == null)
                              throw new Error("Failed Exchange");
                          item = other;
  
                      }
                      if (right != null) {
                          item.value = LoopHelpers.compute2(item.value);
                          Int other = right.exchange(item);
                          if (other == item || other == null)
                              throw new Error("Failed Exchange");
                          item = other;
                      }
                  }
                  barrier.await();
  
              }
              catch (Exception ie) {
                  ie.printStackTrace();
                  return;
              }
          }
      }
  
      static void oneRun(int nthreads, int iters) throws Exception {
          LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
          CyclicBarrier barrier = new CyclicBarrier(nthreads + 1, timer);
          Exchanger<Int> l = null;
          Exchanger<Int> r = new Exchanger<Int>();
          for (int i = 0; i < nthreads; ++i) {
              pool.execute(new Stage(l, r, barrier, iters));
              l = r;
              r = (i+2 < nthreads) ? new Exchanger<Int>() : null;
          }
          barrier.await();
          barrier.await();
          long time = timer.getTime();
          if (print)
              System.out.println(LoopHelpers.rightJustify(time / (iters * nthreads + iters * (nthreads-2))) + " ns per transfer");
      }
  
  }
  