I'm trying to understand the full implication of the intellij
synchronization on non-final fields warning, which has this description:
This inspection reports instances of synchronized statements where the
lock expression is a non-final field. Such statements are unlikely to
have useful semantics, as different threads may be locking on different
objects even when operating on the same object.
An example usage is the following where a multiple operations on the
domainCache variable is done in a synchronized block so that the
remove/insert are atomic:
public class JaasSecurityManager
{
private CachePolicy domainCache;
private Subject updateCache(Principal principal)
{
synchronized( domainCache )
{
if( domainCache.peek(principal) != null )
domainCache.remove(principal);
domainCache.insert(principal, info);
}
}
}
In going over the current memory model docs:
http://www.cs.umd.edu/~pugh/java/memoryModel/
http://gee.cs.oswego.edu/dl/jmm/cookbook.html
http://www.cs.umd.edu/~pugh/java/memoryModel/jsr133.pdf
The only context I can see where this warning applies is if the
domainCache variable is being changed. In that case two threads may
actually be synchronizing/working on different objects, but that is fine
in this case as the atomic block of ops only applies to the domainCache
object. If other state was being referenced I can see a problem, but not
for the illustrated usage.
Am I missing something here?
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Scott Stark
VP Architecture & Technology
JBoss Inc.
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