4:55 p.m.
I talked about this with Emmanuel last night, and we were
a) concerned about the pollution of the API that this implies
b) not sure why we need to do this
So I also spoke to Jason to understand his initial motivation, and from this chat I think
it's clear that things have gone off course here.
Jason raised two issues with modularity/classloading in Infinispan:
1) Using the TCCL as the classloader to load Infinispan classes is a bad idea. Instead we
should use org.infinispan.foo.Bar.getClass().getClassLoader().
2) When we need to load application classes we need a different approach to that used
today. Most of the time the TCCL is perfect for this. However *sometimes* Infinispan may
be invoked outside of the application, when the TCCL may not be set in AS7. Jason and I
discussed three options:
a) require (through a platform integration documentation contract) that the TCCL must
always be set when Infinispan is invoked.
b) Have some sort of InvocationContext which knows what the correct classloader to use is
(aka Hibernate/Seam/Weld design where there is a per-application construct based on a
ThreadLocal). Given this hasn't been designed into the core, it seems like a large
retrofit
c) Make users specify the CL (directly or indirectly) via the API (as we discussed).
Personally I think that (a) is the best approach right now, and is not that onerous a
requirement.
We might want to make the TCCL usage pluggable for OSGI envs. Cc'd David to get his
feedback.
On 4 May 2011, at 10:46, Dan Berindei wrote:
On Wed, May 4, 2011 at 5:09 PM, Pete Muir <pmuir(a)redhat.com>
wrote:
>
> On 4 May 2011, at 05:34, Dan Berindei wrote:
>
>> On Wed, May 4, 2011 at 10:14 AM, Galder Zamarreño <galder(a)redhat.com>
wrote:
>>>
>>> On May 3, 2011, at 2:33 PM, Sanne Grinovero wrote:
>>>
>>>> 2011/5/3 "이희승 (Trustin Lee)" <trustin(a)gmail.com>:
>>>>> On 05/03/2011 05:08 AM, Sanne Grinovero wrote:
>>>>>> 2011/5/2 Manik Surtani <manik(a)jboss.org>:
>>>>>>>
>>>>>>> On 1 May 2011, at 13:38, Pete Muir wrote:
>>>>>>>
>>>>>>>>>> As in, user API? That's a little
intrusive... e.g., put(K, V, cl) ?
>>>>>>>>>
>>>>>>>>> Not for put, since you have the class, just get, and
I was thinking
>>>>>>>>> something more like:
>>>>>>>>>
>>>>>>>>> Foo foo = getUsing(key, Foo.class)
>>>>>>>>
>>>>>>>> This would be a pretty useful addition to the API anyway
to avoid user casts.
>>>>>>>
>>>>>>> Maybe as an "advanced" API, so as not to pollute
the basic API? A bit like:
>>>>>>>
>>>>>>> Foo f =
cache.getAdvancedCache().asClass(Foo.class).get(key);
>>>>>>
>>>>>> doesn't look much better than a cast, but is more cryptical
:)
>>>>>>
>>>>>> getting back to the classloader issue, what about:
>>>>>>
>>>>>> Cache c = cacheManager.getCache( cacheName, classLoader );
>>>>>>
>>>>>> or
>>>>>> Cache c = cacheManager.getCache( cacheName
).usingClassLoader(classLoader );
>>>>>>
>>>>>> BTW if that's an issue on the API, maybe you should propose
it to
>>>>>> JSR-107 as well ?
>>>>>
>>>>> We have a configurable Marshaller, right? Then why don't we just
use
>>>>> the class loader that the current Marshaller uses?
>>>>
>>>> +1
>>>> I like the clean approach, not sure how you configure the "current
>>>> Marshaller" to use the correct CL ?
>>>> Likely hard to do via configuration file :)
>>>
>>> Well, the marshaller is a global component and so it's a cache manager
level. You can't make any assumptions about it's classloader, particularly when
lazy deserialization is configured and you want to make sure that the data of the cache is
deserialized with the correct classloader when the user reads the data from the cache.
This is gonna become even more important when we for example move to having a single cache
for all 2LC entities or all EJB3 SFSBs where we'll definitely need multiple
classloaders to access a single cache.
>>>
>>
>> The current unmarshaller uses the TCCL, which is a great idea for
>> non-modular environments and will still work in AS7 for application
>> classes (so it's still a good default). It probably won't work if
>> Hibernate wants to store its own classes in the cache, because
>> Hibernate's internal classes may not be reachable from the
>> application's classloader.
>>
>> It gets even trickier if Hibernate wants to store a
>> PrivateHibernateCollection class in the cache containing instances of
>> application classes inside. Then I don't think there will be any
>> single classloader that could reach both the Hibernate classes and the
>> application classes so it can properly unmarshal both. Perhaps that's
>> just something for the Hibernate folks to worry about? Or maybe we
>> should allow the users to register more than one classloader with a
>> cache?
>
> You need to use a bridge classloader in this case.
You're right of course, Hibernate must have received/guessed the
application's classloader and so it is able to create a bridge
classloader that "includes" both.
And if the application classes include references to classes from
another module(s), the application has to provide a bridge classloader
to Hibernate anyway.
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