For the sake of simplicity it's probably best if OSGi and non interact only using reflection proxy's and have their own djinn groups so code downloading is unnecessary between them.
At least that's how I'd consider introducing it into an existing djinn.
A jvm that doesn't have version management of some sort may have a lot of
difficulty interacting with services from a framework that can use incompatible
library versions (and that includes service api) side by side.
My concern is interacting with non versioned env's will probably cause the
developer to have to continue dealing with the problems the modular framework
they selected intended solving
Maven and OSGi can probably interact using mvn: codebase annotations, provided
all modules have bundle manifests.
I still support what your doing and find it interesting and don't wish to
discourage you, I think you're likely to admit it will be a difficult
undertaking, but that's probably an attraction right? Maybe River could
provide some interfaces for extensibility where you could plug in?
Regards,
Peter.
Sent from my Samsung device.
Include original message
---- Original message ----
From: "Michał Kłeczek (XPro Sp. z o. o.)"<michal.klec...@xpro.biz>
Sent: 06/02/2017 03:34:54 pm
To:dev@river.apache.org
Subject: Re: OSGi
Once you realize you need some codebase metadata different than mere
list of URLs
the next conclusion is that annotations should be something different
than... a String :)
The next thing to ask is: "what about mixed OSGI and non-OSGI environments"
Then you start to realize you need to abstract over the class loading
environment itself.
Then you start to realize that to support all the scenarios you need to
provide a class loading environment that is "pluggable"
- ie allows using it with other class loading environments and allow the
user to decide which classes should be loaded
by which environment.
This is what I am working on right now :)
Thanks,
Michal
Peter wrote:
My phone sent the previous email before I completed editing.
...If api classes are already loaded locally by client code, then a smart
proxy codebase bundle will resolve imports to those packages (if they're within
the imported version range), when the proxy bundle is downloaded, resolved and
loaded.
The strategy should be, deserialize using the callers context until a class
is not found, then switch to the object containing the current field being
deserialized (which may be a package private implementation class in the
service api bundle) and if that fails use the codebase annotation (the smart
proxy). This is similar in some ways to never preferred, where locally visible
classes will be selected first.
The strategy is to let OSGi do all the dependency wiring from bundle
manifests. Classes not visible will be visible from a common package import
class, except for poorly designed services, which is outside of scope.
Only match api version compatible services.
No allowances made for split packages or other complexities.
If deserialization doesn't succeed, look up another service.
Cheers,
Peter.
Sent from my Samsung device.
Include original message
---- Original message ----
From: Peter<j...@zeus.net.au>
Sent: 06/02/2017 02:59:09 pm
To:dev@river.apache.org<dev@river.apache.org>
Subject: Re: OSGi
Thanks Nic,
If annot
You've identified the reason we need an OSGi specific RMIClassLoaderSpi
implementation; so we can capture and provide Bundle specific annotation
information.
Rmiclassloaderspi's loadClass method expects a ClassLoader to be passed in,
the context ClassLoader is used by PreferredClassProvider when the ClassLoader
argument is null.
Standard Java serialization's OIS walks the call stack and selects the first
non system classloader (it's looking for the application class loader), it
deserializes into the application ClassLoader's context. This doesn't work in
OSGi because the application classes are loaded by a multitude of ClassLoaders.
It also looks like we'll need an OSGi specific InvocationLayerFactory to
capture ClassLoader information to pass to our MarshalInputStream then to our
RMIClassLoaderSpi during deserialization at both endpoints.
We also need to know the bundle (ClassLoader) of the class that calls a
java.lang.reflect.Proxy on the client side, this is actually quite easy to
find, walk the stack, find the Proxy class and obtain the BundleReference /
ClassLoader of the caller.
Currently the java.lang.reflectProxy dynamically generated subclass instance
proxy's ClassLoader is used, this is acceptable when the proxy bytecode is
loaded by the the Client's ClassLoader or smart proxy ClassLoader in the case
where a smart proxy is utilised
If the caller changes, so does the calling context.
Each bundle provides access to all classes within that bundle, including any
public classes from imported packages.
Sent from my Samsung device.
Include original message
---- Original message ----
From: Niclas Hedhman<nic...@hedhman.org>
Sent: 04/02/2017 12:43:28 pm
To:dev@river.apache.org
Subject: Re: OSGi
<snip>
Further, I think the only "sane" approach in a OSGi environment is to
create a new bundle for the Remote environment, all codebases not part of
the API goes into that bundle and that the API is required to be present in
the OSGi environment a priori. I.e. treat the Remote objects in OSGi as it
is treated in plain Java; one classloader, one chunk, sort out its own
serialization woes. Likewise for the server; treat it as ordinary RMI,
without any mumbo-jambo OSGi stuff to be figured out at a non-OSGi-running
JVM. An important difference is that in OSGi, the BundleClassLoader is not
(required to be) a URLClassLoader, so the Java serialization's auto
annotation of globally reachable URLs won't work, and one need to rely on
java.rmi.server.codebase property, but a bundle could watch for loaded
bundles and build that up for URLs that can be resolved globally.
Cheers
--
Niclas Hedhman, Software Developer
http://polygeneapache.org<http://zest.apache.org> - New Energy for Java
