code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.concurrent.ConcurrentHashMap;
  
  /*
   * Copyright 2004 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 4486658
   * @summary thread safety of toArray methods of subCollections
   * @author Martin Buchholz
   */
  
  import java.util.*;
  import java.util.concurrent.*;
  
  public class toArray {
  
      public static void main(String[] args) throws Throwable {
          final Throwable throwable[] = new Throwable[1];
          final int maxSize = 1000;
          final ConcurrentHashMap<Integer, Integer> m
              = new ConcurrentHashMap<Integer, Integer>();
  
          final Thread t1 = new Thread() { public void run() {
              for (int i = 0; i < maxSize; i++)
                  m.put(i,i);}};
  
          final Thread t2 = new Thread() {
              public Throwable exception = null;
              private int prevSize = 0;
  
              private boolean checkProgress(Object[] a) {
                  int size = a.length;
                  if (size < prevSize) throw new RuntimeException("WRONG WAY");
                  if (size > maxSize)  throw new RuntimeException("OVERSHOOT");
                  if (size == maxSize) return true;
                  prevSize = size;
                  return false;
              }
  
              public void run() {
                  try {
                      Integer[] empty = new Integer[0];
                      while (true) {
                          if (checkProgress(m.values().toArray())) return;
                          if (checkProgress(m.keySet().toArray())) return;
                          if (checkProgress(m.values().toArray(empty))) return;
                          if (checkProgress(m.keySet().toArray(empty))) return;
                      }
                  } catch (Throwable t) {
                     throwable[0] = t;
                  }}};
  
          t2.start();
          t1.start();
  
          t1.join();
          t2.join();
  
          if (throwable[0] != null)
              throw throwable[0];
      }
  }
  