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 SimpleFairReentrantLockLoops {
      static final ExecutorService pool = Executors.newCachedThreadPool();
      static final LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom();
      static boolean print = false;
      static int iters = 2000000;
  
      public static void main(String[] args) throws Exception {
          int maxThreads = 100;
          if (args.length > 0)
              maxThreads = Integer.parseInt(args[0]);
  
          new ReentrantLockLoop(1).test();
          new ReentrantLockLoop(1).test();
          print = true;
  
          int k = 1;
          for (int i = 1; i <= maxThreads;) {
              System.out.print("Threads: " + i);
              new ReentrantLockLoop(i).test();
              Thread.sleep(100);
              if (i == k) {
                  k = i << 1;
                  i = i + (i >>> 1);
              }
              else
                  i = k;
          }
          pool.shutdown();
      }
  
      static final class ReentrantLockLoop implements Runnable {
          private int v = rng.next();
          private volatile int result = 17;
          private final ReentrantLock lock = new ReentrantLock(true);
          private final LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
          private final CyclicBarrier barrier;
          private final int nthreads;
          private volatile int readBarrier;
          ReentrantLockLoop(int nthreads) {
              this.nthreads = nthreads;
              barrier = new CyclicBarrier(nthreads+1, timer);
          }
  
          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();
                  long tpi = time / ((long) iters * nthreads);
                  System.out.print("\t" + LoopHelpers.rightJustify(tpi) + " ns per lock");
                  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() {
              final ReentrantLock lock = this.lock;
              try {
                  barrier.await();
                  int sum = v + 1;
                  int x = 0;
                  int n = iters;
                  while (n-- > 0) {
                      lock.lock();
                      int k = (sum & 3);
                      if (k > 0) {
                          x = v;
                          while (k-- > 0)
                              x = LoopHelpers.compute6(x);
                          v = x;
                      }
                      else x = sum + 1;
                      lock.unlock();
                      if ((x += readBarrier) == 0)
                          ++readBarrier;
                      for (int l = x & 7; l > 0; --l)
                          sum += LoopHelpers.compute6(sum);
                  }
                  barrier.await();
                  result += sum;
              }
              catch (Exception ie) {
                  return;
              }
          }
      }
  
  }
  