TCCL memory leak in RMI registry creation

Stuart Marks stuart.marks at
Thu Apr 21 22:32:05 UTC 2016

Hi Mark,

Is it possible to save the reference to the registry that was created by the 
call to LocateRegistry.createRegistry()? If so, then it's possible to shut down 
that registry by exporting it:

     UnicastRemoteObject.unexportObject(registry, true);

Adding this to the "RegistryLeak" test program you posted changes its behavior 
to print "no leak". (I haven't looked at this too closely, though, so I may be 
misinterpreting what's going on.)

It's probably necessary to unexport and maybe also unbind everything from this 
registry as well, as Roger had suggested previously.


On 4/21/16 6:53 AM, Mark Thomas wrote:
> Continuing the previous thread but with a more precise subject.
> Calling
> LocateRegistry.createRegistry(Registry.REGISTRY_PORT);
> is sufficient to pin the Thread Context Class Loader (TCCL) in memory
> with no public API available (that I can find) to remove the reference.
> This is a problem for modular environments like Java EE containers that
> can frequently load and unload modules since it will trigger a memory
> leak. I have made a simple Java class that demonstrates this issue
> available on GitHub. [1]
> Up to and including Java 8, it is possible to use reflection tricks [2]
> to a) identify these leaks and b) fix them. As of Java 9, these
> reflection tricks will be blocked.
> Being able to identify and fix these memory leaks has been extremely
> useful in resolving issues with memory leaks with multiple deployments
> in Java EE environments.
> I believe that equivalent functionality needs to be available in Java 9
> onwards. I have no strong views on what that functionality should look
> like as long as it enables the leaks to be identified and, ideally,
> resolved.
> Looking at the source code for sun.rmi.transport.Target, the ccl field
> was added for good reason and needs to be retained. That suggests that
> the solution is likely to involve destroying a currently existing
> registry. While Registry.destroy() (or similar) would be sufficient for
> application developers to do the 'right thing' it would not be
> sufficient for container developers to identify that an application
> running on the container had done the 'wrong thing' and needed to be
> fixed. For that something along these lines would be required:
> LocateRegsitry.listRegistries()
> Registry.getThreadContextClassLoader()
> Registry.destroy()
> Assuming my analysis is correct, thoughts on the above solution or any
> alternative solution welcome. For example, a way to hack around the Java
> 9 restrictions would be sufficient.
> Thanks,
> Mark
> [1]
> [2]

More information about the core-libs-dev mailing list