code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.WeakHashMap;
  
  /*
   * Copyright 2007 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 6499848
   * @ignore until 6842353 is resolved
   * @summary Check that iterators work properly in the presence of
   *          concurrent finalization and removal of elements.
   */
  
  import java.util.*;
  import java.util.concurrent.CountDownLatch;
  
  public class GCDuringIteration {
      static void finalizeTillYouDrop() {
          System.gc();              // Enqueue all finalizables
  
          System.runFinalization(); // Drain finalizer queue
  
          // There may be a straggler finalizable object still being
          // finalized by the dedicated finalizer thread.  Enqueue one
          // more finalizable object, and wait for it to be finalized.
          final CountDownLatch latch = new CountDownLatch(1);
          new Object() { protected void finalize() { latch.countDown(); }};
          System.gc();
          try { latch.await(); }
          catch (InterruptedException ie) { throw new Error(ie); }
      }
  
      // A class with the traditional pessimal hashCode implementation,
      // to ensure that all instances end up in the same bucket.
      static class Foo { public int hashCode() { return 42; }}
  
      <K,V> void put(Map<K,V> map, K k, V v) {
          check(! map.containsKey(k));
          equal(map.get(k), null);
          equal(map.put(k, v), null);
          equal(map.get(k), v);
          check(map.containsKey(k));
          equal(map.put(k, v), v);
          equal(map.get(k), v);
          check(map.containsKey(k));
          check(! map.isEmpty());
          equal(map.keySet().iterator().next(), k);
          equal(map.values().iterator().next(), v);
      }
  
      void checkIterator(final Iterator<Map.Entry<Foo, Integer>> it, int first) {
          final Random rnd = new Random();
          for (int i = first; i >= 0; --i) {
              if (rnd.nextBoolean()) check(it.hasNext());
              equal(it.next().getValue(), i);
          }
          if (rnd.nextBoolean())
              THROWS(NoSuchElementException.class,
                     new F(){void f(){it.next();}});
          if (rnd.nextBoolean())
              check(! it.hasNext());
      }
  
      <K,V> V firstValue(Map<K,V> map) {
          return map.values().iterator().next();
      }
  
      void test(String[] args) throws Throwable {
          final int n = 10;
          // Create array of strong refs
          final Foo[] foos = new Foo[2*n];
          final Map<Foo,Integer> map = new WeakHashMap<Foo,Integer>(foos.length);
          check(map.isEmpty());
          equal(map.size(), 0);
  
          for (int i = 0; i < foos.length; i++) {
              Foo foo = new Foo();
              foos[i] = foo;
              put(map, foo, i);
          }
          equal(map.size(), foos.length);
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              foos[first] = null; finalizeTillYouDrop();
              equal(map.size(), first);
              checkIterator(it, first-1);
              equal(map.size(), first);
              equal(firstValue(map), first-1);
          }
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              it.next();          // protects first entry
              System.out.println(map.values());
              foos[first] = null; finalizeTillYouDrop();
              equal(map.size(), first+1);
              System.out.println(map.values());
              checkIterator(it, first-1);
              finalizeTillYouDrop(); // first entry no longer protected
              equal(map.size(), first);
              equal(firstValue(map), first-1);
          }
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              it.next();          // protects first entry
              System.out.println(map.values());
              foos[first] = foos[first-1] = null; finalizeTillYouDrop();
              equal(map.size(), first);
              equal(firstValue(map), first);
              System.out.println(map.values());
              checkIterator(it, first-2);
              finalizeTillYouDrop(); // first entry no longer protected
              equal(map.size(), first-1);
              equal(firstValue(map), first-2);
          }
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              it.next();          // protects first entry
              it.hasNext();       // protects second entry
              System.out.println(map.values());
              foos[first] = foos[first-1] = null; finalizeTillYouDrop();
              equal(firstValue(map), first);
              equal(map.size(), first+1);
              System.out.println(map.values());
              checkIterator(it, first-1);
              finalizeTillYouDrop(); // first entry no longer protected
              equal(map.size(), first-1);
              equal(firstValue(map), first-2);
          }
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              it.next();          // protects first entry
              System.out.println(map.values());
              foos[first] = foos[first-1] = null; finalizeTillYouDrop();
              it.remove();
              equal(firstValue(map), first-2);
              equal(map.size(), first-1);
              System.out.println(map.values());
              checkIterator(it, first-2);
              finalizeTillYouDrop();
              equal(map.size(), first-1);
              equal(firstValue(map), first-2);
          }
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              it.next();          // protects first entry
              it.remove();
              it.hasNext();       // protects second entry
              System.out.println(map.values());
              foos[first] = foos[first-1] = null; finalizeTillYouDrop();
              equal(firstValue(map), first-1);
              equal(map.size(), first);
              System.out.println(map.values());
              checkIterator(it, first-1);
              finalizeTillYouDrop();
              equal(map.size(), first-1);
              equal(firstValue(map), first-2);
          }
  
          {
              int first = firstValue(map);
              final Iterator<Map.Entry<Foo,Integer>> it = map.entrySet().iterator();
              it.hasNext();       // protects first entry
              Arrays.fill(foos, null);
              finalizeTillYouDrop();
              equal(map.size(), 1);
              System.out.println(map.values());
              equal(it.next().getValue(), first);
              check(! it.hasNext());
              finalizeTillYouDrop();
              equal(map.size(), 0);
              check(map.isEmpty());
          }
      }
  
      //--------------------- 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 + " not equal to " + y);}
      public static void main(String[] args) throws Throwable {
          new GCDuringIteration().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");}
      abstract class F {abstract void f() throws Throwable;}
      void THROWS(Class<? extends Throwable> k, F... fs) {
          for (F f : fs)
              try {f.f(); fail("Expected " + k.getName() + " not thrown");}
              catch (Throwable t) {
                  if (k.isAssignableFrom(t.getClass())) pass();
                  else unexpected(t);}}
  }
  