Re: [infinispan-dev] [Pull Request] Modular Classloading Compatibility
On 5/12/11 4:18 AM, Dan Berindei wrote:
On Wed, May 11, 2011 at 11:18 PM, David
Bosschaert<david(a)redhat.com> wrote:
> On 11/05/2011 17:54, Dan Berindei wrote:
>> On Wed, May 11, 2011 at 7:08 PM, Pete Muir<pmuir(a)redhat.com> wrote:
>>> Were we developing for OSGi I would certainly agree with you. However in many
environments today we can reasonably expect the TCCL to be set and to be able to load the
classes we need. So whilst making it part of the API is the safest option, it's also
making complicated an API for the sake of the few at the cost of the many. Further this
also seems kinda nasty to me. We know the class (and hence bundle/module) when we put the
object into Infinispan, therefore why do we require people to respecify this again?
>>>
>>> David, can we not actually do something here akin to what we are discussing
for Weld? Whereby we can serialize out the bundle id and then find the correct CL based on
that when we deserialize.
>> What if the object is a java.util.ArrayList? Each element in the list
>> could belong to a different bundle, so you'd have to write a bundle id
>> for every element in the list.
> Yes, if you know the Bundle-SymbolicName and Version (or the Bundle ID)
> you can find its classloader.
>
> On the other question, if you're passing in a class object then you can
> obtain its classloader and hence the bundle where it came from. But, and
> I think this is what Dan allused to above, is it always true that the
> class your passing in comes from the bundle that you need to have or
> could it also come from one of its parent class loaders?
>
Exactly David, sorry if my message was a little cryptic. I think in
order to handle every case properly you would have to go through the
entire object graph being stored in the cache in order to find all the
classloaders/bundle ids that you will need on get().
This approach just doesn't scale, and it would not work in all
environments (there is no gaurantee you can get the original classloader
if the environment doesn't allow you to look them up by some kind of
unique id).
That seems like a lot of overhead to me, and forcing the user to
provide the classloader doesn't seem that bad in comparison. Perhaps
we should use something other than a thread-local for this though
Yes thread locals are brittle, and tend to leak if they aren't managed
correctly. Using a context specific instance is a much better approach.
so
that users can do a onto the result of a
cacheManager.getCache("A").usingClassLoader(A.class) and never have to
provide the classloader again.
That's similar to what I was proposing with the CacheSession notion. The
basic notion is that you move thread/context specific state to a
separate object that the caller uses (optionaly), and it mirrors the
same Cache API.
In fact I think this is a good idea for the invocation flags we
already have, too. It would involve creating lots of overloads in
CacheDelegate with a PreInvocationContext parameter and a new
CacheDelegateWithContext class to invoke those methods, but the public
API would remain the same.
You dont need to reuse the same impl. Just create a new delegate which
passes an extra invocation state parameter with ever call. The overhead
of that is tiny.
--
Jason T. Greene
JBoss, a division of Red Hat