code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.loops;
  
  /*
   * 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
   */
  
  import java.util.concurrent.*;
  import java.util.concurrent.locks.*;
  import java.util.*;
  
  public final class LockOncePerThreadLoops {
      static final ExecutorService pool = Executors.newCachedThreadPool();
      static final LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom();
      static boolean print = false;
      static int nlocks = 500000;
      static int nthreads = 100;
      static int replications = 20;
  
      public static void main(String[] args) throws Exception {
          if (args.length > 0)
              replications = Integer.parseInt(args[0]);
  
          if (args.length > 1)
              nlocks = Integer.parseInt(args[1]);
  
          print = true;
  
          for (int i = 0; i < replications; ++i) {
              System.out.print("Iteration: " + i);
              new ReentrantLockLoop().test();
              Thread.sleep(100);
          }
          pool.shutdown();
      }
  
      static final class ReentrantLockLoop implements Runnable {
          private int v = rng.next();
          private volatile int result = 17;
          final ReentrantLock[]locks = new ReentrantLock[nlocks];
  
          private final ReentrantLock lock = new ReentrantLock();
          private final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
          private final CyclicBarrier barrier;
          ReentrantLockLoop() {
              barrier = new CyclicBarrier(nthreads+1, timer);
              for (int i = 0; i < nlocks; ++i)
                  locks[i] = new ReentrantLock();
          }
  
          final void test() throws Exception {
              for (int i = 0; i < nthreads; ++i)
                  pool.execute(this);
              barrier.await();
              barrier.await();
              if (print) {
                  long time = timer.getTime();
                  double secs = (double) time / 1000000000.0;
                  System.out.println("\t " + secs + "s run time");
              }
  
              int r = result;
              if (r == 0) // avoid overoptimization
                  System.out.println("useless result: " + r);
          }
  
          public final void run() {
              try {
                  barrier.await();
                  int sum = v;
                  int x = 0;
                  for (int i = 0; i < locks.length; ++i) {
                      locks[i].lock();
                      try {
                              v = x += ~(v - i);
                      }
                      finally {
                          locks[i].unlock();
                      }
                      // Once in a while, do something more expensive
                      if ((~i & 255) == 0) {
                          sum += LoopHelpers.compute1(LoopHelpers.compute2(x));
                      }
                      else
                          sum += sum ^ x;
                  }
                  barrier.await();
                  result += sum;
              }
              catch (Exception ie) {
                  return;
              }
          }
      }
  
  }
  