On Fri, Feb 8, 2013 at 3:41 PM, Galder Zamarreño <galder@redhat.com> wrote:

Hi all,

We've got a small class loading puzzle to solve in our JSR-107 implementation.

JSR-107 has a class called Caching which keeps a singleton enum reference (AFAIK, has same semantics as static) to the systemt's CacheManagerFactory, which in our case it would be InfinispanCacheManagerFactory:
https://github.com/jsr107/jsr107spec/blob/master/src/main/java/javax/cache/Caching.java

A naive user of JSR-107 could decide to use this Caching class in an app server environment and get a reference to the CMF through it, which could cause major classloading issues if we don't protect ourselves.

Within out CMF implementation, we need to keep some kind of mapping which given a name *and* a classloader, which can find the CacheManager instance associated to it.

This poses a potential risk of a static strong reference being held indirectly on the classloader associated with the Infinispan Cache Manager (amongst other sensible components...).

One way to break this strong reference is for CMF implementation to hold a weak reference on the CM as done here:
https://github.com/galderz/infinispan/blob/t_2639/jsr107/src/main/java/org/infinispan/jsr107/cache/InfinispanCacheManagerFactory.java#L56

This poses a problem though in that the Infinispan Cache Manager can be evicted from memory without it's stop/shutdown method being called, leading to resources being left open (i.e. jgroups, jmx…etc).

The only safe way to deal with this that I've thought so far is to have a finalyze() method in InfinispanCacheManager (JSR-107 impl of CacheManager) that makes sure this cache manager is shut down. I'm fully aware this is an expensive operation, but so far is the only way I can see in which we can avoid leaking stuff, while not affecting the actual Infinispan core module.

I've found a good example of this in https://github.com/jbossas/jboss-as/blob/master/controller-client/src/main/java/org/jboss/as/controller/client/impl/RemotingModelControllerClient.java - It even tracks creation time so that if all references to InfinispanCacheManager are lost but the ICM instance is not closed, it will print a warm message.

If anyone has any other thoughts, it'd be interesting to hear about them.

The Caching javadoc seems to prohibit stopping the CacheManagers without user intervention (https://github.com/jsr107/jsr107spec/blob/master/src/main/java/javax/cache/Caching.java#L35):

 * Also keeps track of all CacheManagers created by the factory. Subsequent calls
 * to {@link #getCacheManager()} return the same CacheManager.

And in the javadoc of Caching.close() (https://github.com/jsr107/jsr107spec/blob/master/src/main/java/javax/cache/Caching.java#L153):

     * All cache managers obtained from the factory are shutdown.
     * <p/>
     * Subsequent requests from this factory will return different cache managers than would have been obtained before

     * shutdown. So for example

     * <pre>
     *  CacheManager cacheManager = CacheFactory.getCacheManager();

     *  assertSame(cacheManager, CacheFactory.getCacheManager());
     *  CacheFactory.close();


     *  assertNotSame(cacheManager, CacheFactory.getCacheManager());
     * </pre>

We can't guarantee that getCacheManager() will return the same instance unless we keep a hard reference to it in our CacheManagerFactory. So I think the only option is to add a finalize() method to CacheManagerFactory that will stop all the CacheManagers if the user didn't explicitly call Caching.close().

Cheers

Dan

Cheers,
--
Galder Zamarreño
galder@redhat.com
twitter.com/galderz

Project Lead, Escalante
http://escalante.io

Engineer, Infinispan
http://infinispan.org

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