[jboss-jira] [JBoss JIRA] Created: (JBAS-5364) UnifiedInvokerHAProxy can throw NullPointerException under load

[Galder Zamarreno (JIRA)]

UnifiedInvokerHAProxy can throw NullPointerException under load
---------------------------------------------------------------

                 Key: JBAS-5364
                 URL: http://jira.jboss.com/jira/browse/JBAS-5364
             Project: JBoss Application Server
          Issue Type: Bug
      Security Level: Public (Everyone can see)
          Components: Clustering
    Affects Versions: JBossAS-5.0.0.Beta4, JBossAS-4.2.2.GA
            Reporter: Galder Zamarreno
         Assigned To: Galder Zamarreno


Under heavy load and sharing an EJB proxy between different threads, there's a 
chance of NullPointerException like the one below being reported, specially when 
using proxies configured with RoundRobin as load balance policy, such as SLSBs 
or EJB2 home proxies:

java.lang.NullPointerException

	at org.jboss.invocation.unified.interfaces.UnifiedInvokerHAProxy.invoke(UnifiedInvokerHAProxy.java:186)

	at org.jboss.invocation.InvokerInterceptor.invokeInvoker(InvokerInterceptor.java:365)

	at org.jboss.invocation.MarshallingInvokerInterceptor.invoke(MarshallingInvokerInterceptor.java:63)

	at org.jboss.proxy.ejb.RetryInterceptor.invoke(RetryInterceptor.java:176)

	at org.jboss.proxy.TransactionInterceptor.invoke(TransactionInterceptor.java:61)

	at org.jboss.proxy.SecurityInterceptor.invoke(SecurityInterceptor.java:70)

	at org.jboss.proxy.ejb.HomeInterceptor.invoke(HomeInterceptor.java:184)

	at org.jboss.proxy.ClientContainer.invoke(ClientContainer.java:100)

	at $Proxy1.create(Unknown Source)


Whenever a new target for an invocation is chosen, init(InvokerLocator locator) 
method in UnifiedInvokerProxy is executed:

   protected void init(InvokerLocator locator)
   {
      this.locator = locator;

      try
      {
         client = createClient(locator, getSubSystem());
         client.connect();
      }
      catch(Exception e)
      {
         log.fatal("Could not initialize UnifiedInvokerProxy.", e);
      }

   }

This method could be executed in paralell to the following in 
UnifiedInvokerHAProxy.invoke(Invocation invocation):

Client clientInstance = getClient(invocation);
log.debug("Making invocation on " + clientInstance.getInvoker().getLocator());

When the new client instance is created, the invoker is null until client.connect() is 
called, so something like this can happen:

1.- T1 (Thread 1) executes getClient(invocation); and returns client#1
2.- T2 (Thread 2) selects a new target for the invocation and calls init(InvokerLocator locator)
3.- T2 calls createClient() and the instance variable client becomes client#2
4.- T1 now calls clientInstance.getInvoker().getLocator() which is now client#2 but 
connect() has not been called on this instance, so results on NPE.

The simplest of all solutions would be to make assignment of client instance thread safe, 
something I already did for JBAS-4815 to get around another thread safety issue.

I'm gonna take the tests I created for JBAS-4815 and use them to replicate something like 
this and check whether the fix for that fixes this as well.

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