code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.Map;
  
  /*
   * Copyright 2008 Sun Microsystems, Inc.  All Rights Reserved.
   * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   *
   * This code is free software; you can redistribute it and/or modify it
   * under the terms of the GNU General Public License version 2 only, as
   * published by the Free Software Foundation.
   *
   * This code is distributed in the hope that it will be useful, but WITHOUT
   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   * version 2 for more details (a copy is included in the LICENSE file that
   * accompanied this code).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
   * CA 95054 USA or visit www.sun.com if you need additional information or
   * have any questions.
   */
  
  /*
   * @test
   * @bug 6612102
   * @summary Test Map implementations for mutual compatibility
   */
  
  import edu.stanford.ppl.concurrent.SnapTreeMap;
  
  import java.util.*;
  import java.util.concurrent.*;
  
  /**
   * Based on the strange scenario required to reproduce
   * (coll) IdentityHashMap.iterator().remove() might decrement size twice
   *
   * It would be good to add more "Lockstep-style" tests to this file.
   */
  public class LockStep {
      void mapsEqual(Map m1, Map m2) {
          equal(m1, m2);
          equal(m2, m1);
          equal(m1.size(), m2.size());
          equal(m1.isEmpty(), m2.isEmpty());
          equal(m1.keySet(), m2.keySet());
          equal(m2.keySet(), m1.keySet());
      }
  
      void mapsEqual(List<Map> maps) {
          Map first = maps.get(0);
          for (Map map : maps)
              mapsEqual(first, map);
      }
  
      void put(List<Map> maps, Object key, Object val) {
          for (Map map : maps)
              map.put(key, val);
          mapsEqual(maps);
      }
  
      void removeLastTwo(List<Map> maps) {
          Map first = maps.get(0);
          int size = first.size();
          Iterator fit = first.keySet().iterator();
          for (int j = 0; j < size - 2; j++)
              fit.next();
          Object x1 = fit.next();
          Object x2 = fit.next();
  
          for (Map map : maps) {
              Iterator it = map.keySet().iterator();
              while (it.hasNext()) {
                  Object x = it.next();
                  if (x == x1 || x == x2)
                      it.remove();
              }
          }
          mapsEqual(maps);
      }
  
      void remove(Map m, Iterator it) {
          int size = m.size();
          it.remove();
          if (m.size() != size-1)
              throw new Error(String.format("Incorrect size!%nmap=%s, size=%d%n",
                                            m.toString(), m.size()));
      }
  
      void test(String[] args) throws Throwable {
          final int iterations = 100;
          final Random r = new Random();
  
          for (int i = 0; i < iterations; i++) {
              List<Map> maps = Arrays.asList(
                  new Map[] {
                      new IdentityHashMap(11),
                      new HashMap(16),
                      new LinkedHashMap(16),
                      new WeakHashMap(16),
                      new Hashtable(16),
                      new TreeMap(),
                      new ConcurrentHashMap(16),
                      new ConcurrentSkipListMap(),
                      new SnapTreeMap() });
  
              for (int j = 0; j < 10; j++)
                  put(maps, r.nextInt(100), r.nextInt(100));
              removeLastTwo(maps);
          }
      }
  
      //--------------------- Infrastructure ---------------------------
      volatile int passed = 0, failed = 0;
      void pass() {passed++;}
      void fail() {failed++; Thread.dumpStack();}
      void fail(String msg) {System.err.println(msg); fail();}
      void unexpected(Throwable t) {failed++; t.printStackTrace();}
      void check(boolean cond) {if (cond) pass(); else fail();}
      void equal(Object x, Object y) {
          if (x == null ? y == null : x.equals(y)) pass();
          else fail((x == null ? null : x.getClass().getName()) + " " + x
                  + " not equal to " + (y == null ? null : y.getClass().getName()) + " " + y);}
      public static void main(String[] args) throws Throwable {
          new LockStep().instanceMain(args);}
      void instanceMain(String[] args) throws Throwable {
          try {test(args);} catch (Throwable t) {unexpected(t);}
          System.out.printf("%nPassed = %d, failed = %d%n%n", passed, failed);
          if (failed > 0) throw new AssertionError("Some tests failed");}
  }
  