[jboss-dev] Classloading and partial deployments

[Mladen Turk]

Adrian Brock wrote:
> On Fri, 2008-10-17 at 11:06 +0200, Mladen Turk wrote:
>> Next thing are partial deployments, where pre-loader
>> would need to figure out if the previous package is already
>> installed (redeployment without reboot) in which case
>> the versioning of the components would either allow
>> to continue doing nothing or refuse to load until
>> reboot is done. The second is common behavior now if a
>> package contains native library references cause they
>> are all referenced in system classloader regardless of
>> actual classloader used (and that is what I wish to
>> resolve basically; packing java and native code inside
>> archive and make everything plug-and-play). 
> 
> That's not true. The native libraries belong to
> the classloader whose class did System.loadLibrary().
> 

I'll double check this, but IIUC the library itself
is listed in some higher classloader and never purged
from there.

> There are issues on some operating systems thta don't
> support loading native code twice.

Or unloading. Think that's why JVM plays safe
and makes that 'run once' on all systems.

> Hotdeploying native code becomes a lottery because
> the native code is unloaded "at random" by the GC
> at some point after the classloader becomes unreferenced.
> 

That's why I'm trying to resolve this.
I cannot actually use the provided classloader for
those kind of modules. They need the interceptor
that will actually decide how to deploy each sub component.


>> There is
>> Java Module API JSR-227 (for Java7 thought)
>> and it defines the native libraries as resource concept,
>> but since (according to the spec) it'll forward the
>> System.loadLibrary() to the defining class loader of
>> the calling class the issue will still remain.
>>
> 
> That's just a change packaging convention similar
> to what OSGi does where the jar contains
> the native code instead of having to put the dll(s) on the
> library path.
> 

Right, and I'd like to create something that
will be usable actually. If the library has
dependencies with that you still need library
path. Even now with jboss-native I created
library dependency list, so I load libraries
in reverse dependency order.

Thanks for giving me some clues. I'll poke in
the existing source, and see how to implement
some thin interceptor.

Regards
-- 
^(TM)