[jboss-as7-dev] thread safety and AS Service implementations...

[Scott Marlow]

I would like to get agreement on whether we still need to protect 
Service instance variables.

 From reading the javadoc in the org.jboss.msc.service.Service class, 
mutable instance variables (in Service implementations) need their own 
thread safety protection.

I had a mutable object reference in class PersistenceUnitService that is 
set in the Service start method and cleared in stop().  Someone reported 
a NPE caused by the same mutable object reference, so I think we need to 
guard against this pattern elsewhere most likely (forum post about NPE 
http://community.jboss.org/message/621316).

https://github.com/scottmarlow/jboss-as/commit/c0f05311680cb936fb1abcb7391d2054e16144c5 
changes the variable to be volatile.  The down side is that the object 
reference won't be cached.

I don't know for sure, that the above code change will fix the NPE, just 
seems likely to me.

Scott