On Thu, Feb 14, 2013 at 4:43 PM, Galder Zamarreño gal...@redhat.com wrote:
On Feb 8, 2013, at 3:35 PM, Dan Berindei dan.berin...@gmail.com wrote:
On Fri, Feb 8, 2013 at 3:41 PM, Galder Zamarreño gal...@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().
A finalize() in CacheManagerFactory does not solve the problem since
there's still a hard reference to the CacheManagerFactory impl from
Caching, and as long as that's not cleared, finalize() won't be executed,
so you're still exposed to a potential leak.
Yeah, that's true.
But note that the opposite is also possible: the user can call
Caching.close() from one web app and it will close all the cache managers
opened from any other web app. I doubt we can protect ourselves against
that...
My initial solution in [1] didn't pass the TCK because the tests don't
keep any hard reference to the cache manager, so they could literally
dissapear from the collection cos there was no other hard cache manager
reference.
An alternative way to solve this is to have a weak hash map with
classloader as weak key:
private final MapClassLoader, MapString, InfinispanCacheManager
cacheManagers =
new WeakHashMapClassLoader, MapString,
InfinispanCacheManager();
However, for this to work, all other references that we keep within
Infinispan of cache managers have to also be weak. I've made this change
and it all works fine now
