Re: About issue SM-343 - Infinite wait prevents clean shutdown

[Jean-Baptiste Onofré]

Thanks Grzesiek for your update.

We will review the issue using your information and update it.

Regards
JB

Grzegorz Kokosiński wrote:

Hi.

Issue: http://issues.apache.org/activemq/browse/SM-343?page=com.atlassian.jira.plugin.ext.subversion%3Asubversion-commits-tabpanel

Lastly I encountered on problem described in this issue. I have looked inside the code and I found what had happened. I hope that it will help someone of You to resolve this isssue.

So this how it looks.

First thread is trying to suspend flow and invokes suspend method on AbstractFlow, so it takes monitor of this object because this method is synchronized. But it does not lock writeLock for this moment.

The second thread is trying to execute send method. So it locks readLock, then invokes doSend method of class SedaFlow, then inside this method it invokes enqueuePacket method and tries to create queue by method createQueue. But this method is synchronized, and monitor of this object is taken by first thread, so it cannot execute it till the first thread will leave suspend method. But first thread is trying to lock writeLock, but it cannot do that, because second thread lock readLock... and we have deadlock.

I have copied some of code, maybe it will be helpful.

AbstractFlow.java (servicemix-3.3.1)
116     public void send(MessageExchange me) throws JBIException {
117         if (log.isDebugEnabled()) {
118             log.debug("Called Flow send");
119         }
120         // do send
121         try {
122             lock.readLock().lock();
123             doSend((MessageExchangeImpl) me);
124         } finally {
125             lock.readLock().unlock();
126         }
127     }
AbstractFlow.java (servicemix-3.3.1)

132     public synchronized void suspend() {
133         if (log.isDebugEnabled()) {
134             log.debug("Called Flow suspend");
135         }
136         lock.writeLock().lock();
137         suspendThread = Thread.currentThread();
138     }

SedaFlow.java (servicemix-3.3.1)

176 protected void enqueuePacket(MessageExchangeImpl me) throws JBIException {

177         ComponentNameSpace cns = me.getDestinationId();
178         SedaQueue queue = queueMap.get(cns);
179         if (queue == null) {
180             queue = createQueue(cns);
181         }
182         try {
183             queue.enqueue(me);
184         } catch (InterruptedException e) {

185 throw new MessagingException(queue + " Failed to enqueue exchange: " + me, e);

186         }
187     }
188

189 protected synchronized SedaQueue createQueue(ComponentNameSpace cns) throws JBIException {

Grzesiek