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.*;
  import java.util.concurrent.*;
  
  public class CollectionLoops {
      static int pinsert     = 100;
      static int premove     = 1;
      static int maxThreads  = 48;
      static int removesPerMaxRandom;
      static int insertsPerMaxRandom;
      static volatile int checkSum = 0;
      static boolean print = false;
  
      static final ExecutorService pool = Executors.newCachedThreadPool();
  
      public static void main(String[] args) throws Exception {
          int nkeys       = 10000;
          int nops        = 100000;
  
          Class collectionClass = null;
          if (args.length > 0) {
              try {
                  collectionClass = Class.forName(args[0]);
              } catch (ClassNotFoundException e) {
                  throw new RuntimeException("Class " + args[0] + " not found.");
              }
          }
  
          if (args.length > 1)
              maxThreads = Integer.parseInt(args[1]);
  
          if (args.length > 2)
              nkeys = Integer.parseInt(args[2]);
  
          if (args.length > 3)
              pinsert = Integer.parseInt(args[3]);
  
          if (args.length > 4)
              premove = Integer.parseInt(args[4]);
  
          if (args.length > 5)
              nops = Integer.parseInt(args[5]);
  
          // normalize probabilities wrt random number generator
          removesPerMaxRandom = (int)(((double)premove/100.0 * 0x7FFFFFFFL));
          insertsPerMaxRandom = (int)(((double)pinsert/100.0 * 0x7FFFFFFFL));
  
          System.out.print("Class: " + collectionClass.getName());
          System.out.print(" threads: " + maxThreads);
          System.out.print(" size: " + nkeys);
          System.out.print(" ins: " + pinsert);
          System.out.print(" rem: " + premove);
          System.out.print(" ops: " + nops);
          System.out.println();
  
          // warmup
          test(1, 100, 100, collectionClass);
          test(2, 100, 100, collectionClass);
          test(4, 100, 100, collectionClass);
          print = true;
  
          int k = 1;
          int warmups = 2;
          for (int i = 1; i <= maxThreads;) {
              Thread.sleep(100);
              test(i, nkeys, nops, collectionClass);
              if (warmups > 0)
                  --warmups;
              else if (i == k) {
                  k = i << 1;
                  i = i + (i >>> 1);
              }
              else if (i == 1 && k == 2) {
                  i = k;
                  warmups = 1;
              }
              else
                  i = k;
          }
          pool.shutdown();
      }
  
      static Integer[] makeKeys(int n) {
          LoopHelpers.SimpleRandom rng = new LoopHelpers.SimpleRandom();
          Integer[] key = new Integer[n];
          for (int i = 0; i < key.length; ++i)
              key[i] = new Integer(rng.next());
          return key;
      }
  
      static void shuffleKeys(Integer[] key) {
          Random rng = new Random();
          for (int i = key.length; i > 1; --i) {
              int j = rng.nextInt(i);
              Integer tmp = key[j];
              key[j] = key[i-1];
              key[i-1] = tmp;
          }
      }
  
      static void test(int i, int nk, int nops, Class collectionClass) throws Exception {
          if (print)
              System.out.print("Threads: " + i + "\t:");
          Collection<Integer> collection = (Collection<Integer>)collectionClass.newInstance();
          Integer[] key = makeKeys(nk);
          // Uncomment to start with a non-empty table
          for (int j = 0; j < nk; j += 2)
              collection.add(key[j]);
          shuffleKeys(key);
          LoopHelpers.BarrierTimer timer = new LoopHelpers.BarrierTimer();
          CyclicBarrier barrier = new CyclicBarrier(i+1, timer);
          for (int t = 0; t < i; ++t)
              pool.execute(new Runner(t, collection, key, barrier, nops));
          barrier.await();
          barrier.await();
          long time = timer.getTime();
          long tpo = time / (i * (long) nops);
          if (print)
              System.out.print(LoopHelpers.rightJustify(tpo) + " ns per op");
          double secs = (double) time / 1000000000.0;
          if (print)
              System.out.print("\t " + secs + "s run time");
          if (checkSum == 0) System.out.print(" ");
          if (print)
              System.out.println();
          collection.clear();
      }
  
      static class Runner implements Runnable {
          final Collection<Integer> collection;
          final Integer[] key;
          final LoopHelpers.SimpleRandom rng;
          final CyclicBarrier barrier;
          int position;
          int total;
          int nops;
  
          Runner(int id, Collection<Integer> collection, Integer[] key,  CyclicBarrier barrier, int nops) {
              this.collection = collection;
              this.key = key;
              this.barrier = barrier;
              this.nops = nops;
              position = key.length / (id + 1);
              rng = new LoopHelpers.SimpleRandom((id + 1) * 8862213513L);
              rng.next();
          }
  
          public void run() {
              try {
                  barrier.await();
                  int p = position;
                  int ops = nops;
                  Collection<Integer> c = collection;
                  while (ops > 0) {
                      int r = rng.next();
                      p += (r & 7) - 3;
                      while (p >= key.length) p -= key.length;
                      while (p < 0) p += key.length;
  
                      Integer k = key[p];
                      if (c.contains(k)) {
                          if (r < removesPerMaxRandom) {
                              if (c.remove(k)) {
                                  p = Math.abs(total % key.length);
                                  ops -= 2;
                                  continue;
                              }
                          }
                      }
                      else if (r < insertsPerMaxRandom) {
                          ++p;
                          ops -= 2;
                          c.add(k);
                          continue;
                      }
  
                      total += LoopHelpers.compute6(k.intValue());
                      --ops;
                  }
                  checkSum += total;
                  barrier.await();
              }
              catch (Exception ex) {
                  throw new RuntimeException(ex);
              }
          }
      }
  }
  