[jboss-jira] [JBoss JIRA] Created: (JBREM-1227) Fix deadlock between MicroRemoteClientInvoker and RemotingClassLoader

[Ron Sigal (JIRA)]

Fix deadlock between MicroRemoteClientInvoker and RemotingClassLoader
---------------------------------------------------------------------

                 Key: JBREM-1227
                 URL: https://jira.jboss.org/browse/JBREM-1227
             Project: JBoss Remoting
          Issue Type: Bug
      Security Level: Public (Everyone can see)
    Affects Versions: 2.5.2.SP3 (Flounder)
            Reporter: Ron Sigal
            Assignee: Ron Sigal
             Fix For: 2.5.2.SP4 (Flounder) 


The following deadlock can occur:

1. Thread T1 reads a response with an object whose class is not available locally, so it uses its org.jboss.remoting.loading.RemotingClassLoader to try to download the class

    a. java.lang.ClassLoader.loadClassInternal() acquires a lock on itself (an instance of RemotingClassLoader)
    
    b. RemotingClassLoader uses its copy of an org.jboss.remoting.loading.ClassByteClassLoader to try to download the class
    
    c. ClassByteClassLoader calls org.jboss.remoting.MicroRemoteClientInvoker.invoke(), which tries to synchronize on MicroRemoteClientInvoker.class as it sets up an UnMarshaller with a ClassLoader
    
2. Thread T2 attempts to make an invocation

   a. MicroRemoteClientInvoker.invoke() acquires a lock on MicroRemoteClientInvoker.class
   
   b. MicroRemoteClientInvoker.invoke() calls the synchronized method RemotingClassLoader.setUserClassLoader(), which tries to acquire a lock on the RemotingClassLoader
   
Deadlock.

The only two synchronized methods in RemotingClassLoader are setUserClassLoader() and unsetUserClassLoader(), which are both called from MicroRemoteClientInvoker.invoke().  The call to setUserClassLoader() is already done while the MicroRemoteClientInvoker.class lock is held.  If the call to unsetUserClassLoader() is made with the same lock, then setUserClassLoader() and unsetClassLoader() don't have to be synchronized.  That will eliminate the deadlock because step 2b is removed.

-- 
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators: https://jira.jboss.org/secure/Administrators.jspa
-
For more information on JIRA, see: http://www.atlassian.com/software/jira