BUG in JDK6 ReentrantReadWriteLock can cause SMX hang when redeploy SA
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Key: SM-1824
URL: https://issues.apache.org/activemq/browse/SM-1824
Project: ServiceMix
Issue Type: Bug
Affects Versions: 3.3, 3.2.3
Environment: Java version: 1.6.0_06
OS name: "linux" version: "2.6.9-42.elsmp" arch: "i386" Family: "unix"
Reporter: Freeman Fang
Look at this test code
{code}
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 TestTryWriteInRead {
void log(String s) {
System.out.printf("%s: %s%n", Thread.currentThread().getName(), s);
}
public static void main(String[] args) throws Exception {
new TestTryWriteInRead().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();
}
}
}
}
{code}
Run this code with JDK 5 we get the expected behavior , the console output is
TryWrite0: try get writelock
TryRead0: try get readlock
TryRead0: can get readlock
TryRead0: unlock readlock,
rwLock.readLock() can get readLock in trhead with name TryRead0
But run this code with JDK 6 we get console output like
TryWrite0: try get writelock
TryRead0: try get readlock
which means can't get readLock even there is no other thread hold the
writeLock, that's conflict with the JDK API DOC.
Actually this test code is the abstraction of the behavior when we redeploy
SAs, especially at the same time externel client still send message to the
endpoint.
We can find the ReentrantReadWrite used in AbstractFlow, and in some case if
the ReentrantReadWrite read and write lock accquire seqence is same as the test
code, then the SMX bus hang.
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