code: // from gee.cs.oswego.edu/home/jsr166/jsr166
  
  package jsr166tests.jtreg.util.concurrent.locks.ReentrantReadWriteLock;
  
  /*
   * Copyright 2005-2008 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 6207928 6328220 6378321 6625723
   * @summary Recursive lock invariant sanity checks
   * @author Martin Buchholz
   */
  
  import java.io.*;
  import java.util.*;
  import java.util.concurrent.*;
  import java.util.concurrent.locks.*;
  
  // I am the Cownt, and I lahve to cownt.
  public class Count {
      final Random rnd = new Random();
  
      void lock(Lock lock) {
          try {
              switch (rnd.nextInt(4)) {
              case 0: lock.lock(); break;
              case 1: lock.lockInterruptibly(); break;
              case 2: check(lock.tryLock()); break;
              case 3: check(lock.tryLock(45, TimeUnit.MINUTES)); break;
              }
          } catch (Throwable t) { unexpected(t); }
      }
  
      void test(String[] args) throws Throwable {
          for (boolean fair : new boolean[] { true, false })
              for (boolean serialClone : new boolean[] { true, false }) {
                  testReentrantLocks(fair, serialClone);
                  testConcurrentReadLocks(fair, serialClone);
              }
      }
  
      void testConcurrentReadLocks(final boolean fair,
                                   final boolean serialClone) throws Throwable {
          final int nThreads = 10;
          final CyclicBarrier barrier = new CyclicBarrier(nThreads);
          final ExecutorService es = Executors.newFixedThreadPool(nThreads);
          final ReentrantReadWriteLock rwl = serialClone ?
              serialClone(new ReentrantReadWriteLock(fair)) :
              new ReentrantReadWriteLock(fair);
          for (int i = 0; i < nThreads; i++) {
              es.submit(new Runnable() { public void run() {
                  try {
                      int n = 5;
                      for (int i = 0; i < n; i++) {
                          barrier.await();
                          equal(rwl.getReadHoldCount(), i);
                          equal(rwl.getWriteHoldCount(), 0);
                          check(! rwl.isWriteLocked());
                          equal(rwl.getReadLockCount(), nThreads * i);
                          barrier.await();
                          lock(rwl.readLock());
                      }
                      for (int i = 0; i < n; i++) {
                          rwl.readLock().unlock();
                          barrier.await();
                          equal(rwl.getReadHoldCount(), n-i-1);
                          equal(rwl.getReadLockCount(), nThreads*(n-i-1));
                          equal(rwl.getWriteHoldCount(), 0);
                          check(! rwl.isWriteLocked());
                          barrier.await();
                      }
                      THROWS(IllegalMonitorStateException.class,
                             new F(){void f(){rwl.readLock().unlock();}},
                             new F(){void f(){rwl.writeLock().unlock();}});
                      barrier.await();
                  } catch (Throwable t) { unexpected(t); }}});}
          es.shutdown();
          check(es.awaitTermination(10, TimeUnit.SECONDS));
      }
  
      void testReentrantLocks(final boolean fair,
                              final boolean serialClone) throws Throwable {
          final ReentrantLock rl = serialClone ?
              serialClone(new ReentrantLock(fair)) :
              new ReentrantLock(fair);
          final ReentrantReadWriteLock rwl = serialClone ?
              serialClone(new ReentrantReadWriteLock(fair)) :
              new ReentrantReadWriteLock(fair);
          final int depth = 10;
          equal(rl.isFair(), fair);
          equal(rwl.isFair(), fair);
          check(! rl.isLocked());
          check(! rwl.isWriteLocked());
          check(! rl.isHeldByCurrentThread());
          check(! rwl.isWriteLockedByCurrentThread());
          check(! rwl.writeLock().isHeldByCurrentThread());
  
          for (int i = 0; i < depth; i++) {
              equal(rl.getHoldCount(), i);
              equal(rwl.getReadLockCount(), i);
              equal(rwl.getReadHoldCount(), i);
              equal(rwl.getWriteHoldCount(), i);
              equal(rwl.writeLock().getHoldCount(), i);
              equal(rl.isLocked(), i > 0);
              equal(rwl.isWriteLocked(), i > 0);
              lock(rl);
              lock(rwl.writeLock());
              lock(rwl.readLock());
          }
  
          for (int i = depth; i > 0; i--) {
              check(! rl.hasQueuedThreads());
              check(! rwl.hasQueuedThreads());
              check(! rl.hasQueuedThread(Thread.currentThread()));
              check(! rwl.hasQueuedThread(Thread.currentThread()));
              check(rl.isLocked());
              check(rwl.isWriteLocked());
              check(rl.isHeldByCurrentThread());
              check(rwl.isWriteLockedByCurrentThread());
              check(rwl.writeLock().isHeldByCurrentThread());
              equal(rl.getQueueLength(), 0);
              equal(rwl.getQueueLength(), 0);
              equal(rwl.getReadLockCount(), i);
              equal(rl.getHoldCount(), i);
              equal(rwl.getReadHoldCount(), i);
              equal(rwl.getWriteHoldCount(), i);
              equal(rwl.writeLock().getHoldCount(), i);
              rwl.readLock().unlock();
              rwl.writeLock().unlock();
              rl.unlock();
          }
          THROWS(IllegalMonitorStateException.class,
                 new F(){void f(){rl.unlock();}},
                 new F(){void f(){rwl.readLock().unlock();}},
                 new F(){void f(){rwl.writeLock().unlock();}});
      }
  
      //--------------------- 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 Count().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);}}
  
      static byte[] serializedForm(Object obj) {
          try {
              ByteArrayOutputStream baos = new ByteArrayOutputStream();
              new ObjectOutputStream(baos).writeObject(obj);
              return baos.toByteArray();
          } catch (IOException e) { throw new RuntimeException(e); }}
      static Object readObject(byte[] bytes)
          throws IOException, ClassNotFoundException {
          InputStream is = new ByteArrayInputStream(bytes);
          return new ObjectInputStream(is).readObject();}
      @SuppressWarnings("unchecked")
      static <T> T serialClone(T obj) {
          try { return (T) readObject(serializedForm(obj)); }
          catch (Exception e) { throw new RuntimeException(e); }}
  }
  