FULL PRODUCT VERSION :
java version "1.6.0_12"
Java(TM) SE Runtime Environment (build 1.6.0_12-b04)
Java HotSpot(TM) Server VM (build 11.2-b01, mixed mode)


ADDITIONAL OS VERSION INFORMATION :
Linux Freeman-pc 2.6.9-42.ELsmp #1 SMP Wed Jul 12 23:27:17 EDT 2006 i686 i686 i386 GNU/Linux

A DESCRIPTION OF THE PROBLEM :
java version "1.6.0_12"
Java(TM) SE Runtime Environment (build 1.6.0_12-b04)
Java HotSpot(TM) Server VM (build 11.2-b01, mixed mode)
we cannot get a read lock if the sequence is
 * thread 1: rwlock.readLock().lock(); //should sucess to get the readLock
 * thread 2: rwlock.writeLock().lock();//should fail to get the writeLock since the readLock already hold by another thread
 * thread 3: rwlock.readLock().lock(); //should success to get the readLock since no other thread hold the writeLock but failed only with JDK6, (OK with JDK 5)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
run the code like
import java.util.concurrent.locks.*;
import java.util.concurrent.*;

/**
 * Test ReentrantReadWrite Lock.
 * This code shows how we cannot get a read lock if the sequence is
 * thread 1: rwlock.readLock().lock(); //should sucess to get the readLock
 * thread 2: rwlock.writeLock().lock();//should fail to get the writeLock since the readLock already hold by another thread
 * thread 3: rwlock.readLock().lock(); //should success to get the readLock since no other thread hold the writeLock but failed only with JDK6, (OK with JDK 5)
 */
public class TestReadWriteLock {

    void log(String s) {
        System.out.printf("%s: %s%n", Thread.currentThread().getName(), s);
    }


    public static void main(String[] args) throws Exception {

        new TestReadWriteLock().runTest();
    }

    public void runTest() throws Exception {
        ReentrantReadWriteLock rwlock = new ReentrantReadWriteLock(false);

        // obtain read lock
        rwlock.readLock().lock(); //should sucess to get the readLock

        // start 1 threads
        for (int i = 0; i < 1; i++) {
            new Thread(this.new WriteLockThread(rwlock), "TryWrite" + i).start();
            Thread.sleep(3000);
            new Thread(this.new ReadLockThread(rwlock), "TryRead" + i).start();
        }
    }

    class WriteLockThread implements Runnable {

        private ReentrantReadWriteLock rwlock;

        public WriteLockThread(ReentrantReadWriteLock rwlock) {
            this.rwlock = rwlock;
        }
        public void run() {
            try {
                log("try get writelock");
                rwlock.writeLock().lock(); //should fail to get the writeLock since the readLock already hold by another thread
                log("can get writelock"); // can't print out
            } finally {
            }

        }

    }

    class ReadLockThread implements Runnable {

        private ReentrantReadWriteLock rwlock;

        public ReadLockThread(ReentrantReadWriteLock rwlock) {
            this.rwlock = rwlock;
        }
        public void run() {
            try {
                log("try get readlock");
                rwlock.readLock().lock();//should success to get the readLock since no other thread hold the writeLock but failed only with JDK6, (OK with JDK 5)
                log("can get readlock");//get this print out with JDK5 as expected, but not with JDK6, which means the error in JDK6
            } finally {
                log("unlock readlock");
                rwlock.readLock().unlock();
            }

        }

    }
}


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
TryWrite0: try get writelock
TryRead0: try get readlock
TryRead0: can get readlock
TryRead0: unlock readlock
ACTUAL -
TryWrite0: try get writelock
TryRead0: try get readlock

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.util.concurrent.locks.*;
import java.util.concurrent.*;

/**
 * Test ReentrantReadWrite Lock.
 * This code shows how we cannot get a read lock if the sequence is
 * thread 1: rwlock.readLock().lock(); //should sucess to get the readLock
 * thread 2: rwlock.writeLock().lock();//should fail to get the writeLock since the readLock already hold by another thread
 * thread 3: rwlock.readLock().lock(); //should success to get the readLock since no other thread hold the writeLock but failed only with JDK6, (OK with JDK 5)
 */
public class TestReadWriteLock {

    void log(String s) {
        System.out.printf("%s: %s%n", Thread.currentThread().getName(), s);
    }


    public static void main(String[] args) throws Exception {

        new TestReadWriteLock().runTest();
    }

    public void runTest() throws Exception {
        ReentrantReadWriteLock rwlock = new ReentrantReadWriteLock(false);

        // obtain read lock
        rwlock.readLock().lock(); //should sucess to get the readLock

        // start 1 threads
        for (int i = 0; i < 1; i++) {
            new Thread(this.new WriteLockThread(rwlock), "TryWrite" + i).start();
            Thread.sleep(3000);
            new Thread(this.new ReadLockThread(rwlock), "TryRead" + i).start();
        }
    }

    class WriteLockThread implements Runnable {

        private ReentrantReadWriteLock rwlock;

        public WriteLockThread(ReentrantReadWriteLock rwlock) {
            this.rwlock = rwlock;
        }
        public void run() {
            try {
                log("try get writelock");
                rwlock.writeLock().lock(); //should fail to get the writeLock since the readLock already hold by another thread
                log("can get writelock"); // can't print out
            } finally {
            }

        }

    }

    class ReadLockThread implements Runnable {

        private ReentrantReadWriteLock rwlock;

        public ReadLockThread(ReentrantReadWriteLock rwlock) {
            this.rwlock = rwlock;
        }
        public void run() {
            try {
                log("try get readlock");
                rwlock.readLock().lock();//should success to get the readLock since no other thread hold the writeLock but failed only with JDK6, (OK with JDK 5)
                log("can get readlock");//get this print out with JDK5 as expected, but not with JDK6, which means the error in JDK6
            } finally {
                log("unlock readlock");
                rwlock.readLock().unlock();
            }

        }

    }
}

---------- END SOURCE ----------