[infinispan-dev] [Pull Request] Modular Classloading Compatibility

Thu May 19 06:04:49 EDT 2011

On May 19, 2011, at 10:04 AM, Sanne Grinovero wrote:

> 2011/5/19 Dan Berindei <dan.berindei at gmail.com>:
>> On Wed, May 18, 2011 at 7:06 PM, Manik Surtani <manik at jboss.org> wrote:
>>> Hi guys
>>> 
>>> Sorry I've been absent from this thread for a while now (it's been growing faster than I've been able to deal with email backlog!)
>>> 
>>> Anyway, this is a very interesting discussion.  To summarise - as Pete did at some point - there are 2 goals here:
>>> 
>>> 1.  Safe and intuitive use of an appropriate classloader
>>> 2.  Safe type system for return values.
>>> 
>>> I think the far more pressing concern is (1) so I'd like to focus on that.  If we think (2) is pressing enough a concern, we should spawn a separate thread and discuss there.
>>> 
>>> So, onto the issue of safe classloading.
>>> 
>>> 1) Class loader per session/cache.
>>> 
>>> I like Jason/Sanne/Trustin's suggestions of a session-like contract, and specifically I think this is best achieved as a delegate to a cache, again as suggested elsewhere by Pete, etc.  E.g.,
>>> 
>>>        Cache<?, ?> myCache = cacheManager.getCache("myCache", myClassLoader);
>>> 
>>> and what is returned is something that delegates to the actual cache, making sure the TCCL is set and re-set appropriately.  The handle to the cache is effectively your "session" and each webapp, etc in an EE environment will have its own handle.  I propose using the TCCL as an internal implementation detail within this delegate, helps with making sure it is carefully managed and cleaned up while not re-engineering loads of internals.
>>> 
>> 
>> I like the API but I would not recommend using the TCCL for this. I
>> was able to get a nice perf jump in the HotRod client by skipping 2
>> Thread.setContextClassLoader() calls on each cache operation (1 to set
>> the TCCL we wanted and 1 to restore the original TCCL). Setting the
>> TCCL is a privileged operation, so it has to go through a
>> SecurityManager and that is very slow.
>> 
>> 
>>> I think EmbeddedCacheManager.getCache(String name, ClassLoader cl) is enough ... it is clear enough, and I don't see the need for overloaded getCache(name, classOfWhichClassLoaderIWishToUse).
>>> 
>> 
>> I agree, a Cache.usingClassloader(classOfWhichClassLoaderIWishToUse)
>> overload would have made sense because the method name already
>> communicates the intention, but a getCache(name, clazz) overload is
>> too obscure.
>> 
>> 
>>> 2) Class loader per invocation.
>>> 
>>> I've been less than happy with this, not just because it pollutes the API but that it adds a layer of confusion.  If all use cases discussed can be solved with (1) above, then I'd prefer to just do that.
>>> 
>>> The way I see it, most user apps directly using Infinispan would only be exposed to a single class loader per cache reference (even if multiple references talk to the same cache).
>>> 
>>> Frameworks, OTOH, are a bit tougher, Hibernate being a good example on this thread.  So this is a question for Galder - is it feasible to maintain several references to a cache, one for each app/persistence unit?
>>> 
>>> 3) Can all OSGi requirements be handled by (1)? I would guess so, from what I have read here, since the class loader is explicitly passed in when getting a handle on a cache.
>>> 
>> 
>> Yes, the only difference is that OSGi goesn't make any guarantees
>> about the TCCL, so passing the classloader explicitly will work in all
>> environments. However,
>> 
>> 4) What about storeAsBinary="false"? Threads processing requests from
>> other nodes are not associated with any CacheManager.getCache(name,
>> classloader) call, and they also have to unmarshall values with this
>> setting.
>> 
>> Since Hibernate already mandates storeAsBinary="true" for its 2LC, we
>> can probably get away with only supporting one classloader per cache
>> in the storeAsBinary="false" case.
>> 
>> Still, we can't rely on the TCCL of the background threads because
>> those threads are shared between all the caches in a CacheManager. In
>> fact we should probably set the TCCL to null for all background
>> threads created by Infinispan, or we risk keeping the classes of the
>> first application/bundle that called us alive as long as those threads
>> are still running.
>> 
>> Dan
> 
> Totally agree with all you said, great analysis!
> 
> So it looks like that all Caches being shared across different
> classloaders (deployed applications)
> should be used only with storeAsBinary="false", still I'm having some
> doubts about how even that is safe.
> How can we prevent two applications both using hibernate from mixing
> the cache keys and values?

How do you do that? Apps don't have any direct access to the Hibernate Cache.

> I assume the keys being used in the 2LC use entity names or class
> names combined with the primary keys;
> it's totally possible to have multiple applications using the same
> entity names, which is quite common in my experience.

That's what region name comes in. Multiple apps shouldn't have the same region name. That's what discriminates entities in different apps.

> 
> The configurations defined in the app server could be used as
> templates to start/stop specific caches for each deployment,
> generating a unique name depending on the ear/war/.. in such a way to
> be consistent with names on other nodes.
> Was this all designed as a workaround for the fact that we're still
> having trouble in forming a cluster of cachemanagers having different
> caches?
> 
> Sanne
> 
>> 
>> 
>>> Cheers
>>> Manik
>>> 
>>> 
>>> On 27 Apr 2011, at 17:39, Jason T. Greene wrote:
>>> 
>>>> Available here:
>>>> https://github.com/infinispan/infinispan/pull/278
>>>> 
>>>> The problem is basically that infinispan currently is using TCCL for all
>>>> class loading and resource loading. This has a lot of problems in
>>>> modular containers (OSGi, AS7, etc), where you dont have framework
>>>> implementation classes on the same classloader as user classes (that is
>>>> how they achieve true isolation)
>>>> 
>>>> You can read about this in more detail here:
>>>> http://community.jboss.org/wiki/ModuleCompatibleClassloadingGuide
>>>> 
>>>> The patch in the pull request is a first step, and should fix many
>>>> issues, but it does not address all (there is still a lot of TCCL usage
>>>> spread out among cacheloaders and so on), and ultimately it's just a
>>>> work around. It should, however, be compatible in any other non-modular
>>>> environment.
>>>> 
>>>> Really the ultimate solution is to setup a proper demarcation between
>>>> what the user is supposed to provide, and what is expected to be bundled
>>>> with infinispan. Whenever there is something the user can provide a
>>>> class, then the API should accept a classloader to load that class from.
>>>> If it's a class that is just internal wiring of infinispan, then
>>>> Infinispan's defining classloader should always be used.
>>>> 
>>>> The one case I can think of in infnispan where TCCL really makes sense
>>>> is in the case of lazy deserialization from an EE application. However
>>>> that is only guaranteed to work when you are executing in a context that
>>>> has that style of contract (like in an EE component). There are many
>>>> other cases though where someone would expect it to work from a non-EE
>>>> context (e.g. from a thread pool). What you really want is the caller's
>>>> classloader, but that is not cheap to get at, so it's something that
>>>> should be supplied as part of the API interaction (in the case where
>>>> there is no EE context). Alternatively you can just just require that
>>>> folks push/pop TCCL, but users often get this wrong.
>>>> 
>>>> Thanks!
>>>> 
>>>> --
>>>> Jason T. Greene
>>>> JBoss, a division of Red Hat
>>>> _______________________________________________
>>>> infinispan-dev mailing list
>>>> infinispan-dev at lists.jboss.org
>>>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>>> 
>>> --
>>> Manik Surtani
>>> manik at jboss.org
>>> twitter.com/maniksurtani
>>> 
>>> Lead, Infinispan
>>> http://www.infinispan.org
>>> 
>>> 
>>> 
>>> 
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>> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache