Thanks Gregg,
Thoughts inline below.
Cheers,
Peter.
On 27/01/2017 12:35 AM, Gregg Wonderly wrote:
Is there any thought here about how a single client might use both an
OSGi deployed service and a conventionally deployed service?
Not yet, I'm currently considering how to support OSGi by
implementing an
RMIClassLoaderSPI, similar to how Dennis has for Maven in Rio.
I think once a good understanding of OSGi has developed, we can
consider
how an implementation could support that, possibly by exploiting
something
like Pax URL built into PreferredClassProvider.
The ContextClassLoader is a good abstraction mechanism for
finding “the”
approriate class loader. It allows applications to deploy a composite
class loader in some form that would be able to resolve classes
from many
sources and even provide things like preferred classes.
Yes, it works well for conventional frameworks and is utilised by
PreferredClassProvider, but it's use in OSGi is discouraged, I'd
like to
consider how it's use can be avoided in an OSGi env.
In a Java desktop application, would a transition from a background
thread, interacting with a service to get an object from a service
which is
not completely resolved to applicable loaders still resolve
correctly in an
EventDispatch Thread? That event dispatch thread can have the context
class loader set on it by the thread which got the object, to be
the class
loader of the service object, to make sure that the resolution of
classes
happens with the correct class loader such that there will not be a
problem
with the service object having one set of definitions and another
service
or the application classpath having a conflicting class definition
by the
same name.
I’ve had to spend quite a bit of time to make sure that these
scenarios
work correctly in my Swing applications.
Have you got more information? I'm guessing this relates to delayed
unmarshalling into the EventDispatch thread.
It's early days yet, I'm still working it out what information is
required
to resolve the correct ClassLoaders& bundles, but this is an important
question, Bharath mentioned Entry's can be utilised for versioning
and this
seems like a good idea.
What follows are thoughts and observations.
A bundle can be created from a URL, provided the codebase the URL
refers
to has an OSGi bundle manifest, so this could allow any of the
existing URL
formats to deliver a proxy codebase for an OSGi framework. When
OSGi loads
the bundle, the package dependencies will be wired up by the local
env. If
the URL doesn't reference a bundle, then we could use Bharath's
approach
and subclass the client's ClassLoader, this does make all the clients
classes visible to the proxy however, but that would happen anyway in a
standard Jini / River environment.
OSGi gives preference to already loaded bundles when resolving package
dependencies, so the client should be careful not to unmarshall any
proxy's
that might require a higher version than the bundle already
installed when
the client bundle resolved its dependencies.
One of the proxy bundle dependencies will be the service api
bundle. The
proxy bundle can limit the service api package / packages to a specific
version or version range, which it could advertise in an Entry.
Boolean
logic comparison of Entry's would have to be performed locally, after
matching on the service type (this requires delayed unmarshalling to
prevent the resolution of unwanted versions).
So, the OSGi bundles installed in remote JVM's communicating with each
other, may not be exactly the same version, but should be compatible.
Multiple versions of a package or bundle may be available in a JVM,
so we
need to ensure we've selected one imported by the proxy.
We could define a simple rule, that the first URL in an annotation,
must
be the proxy bundle, with all dependencies to be provisioned by the
OSGi
Framework, which would allow the same codebase annotation to be
utilised in
a non OSGi environment, but this will probably mean the loss of any
trailing URL annotations if the proxy's remarshalled.
Once the proxy bundle has been loaded, its ClassLoader needs to be the
default for the remaining stream classes (smart proxy fields), since it
knows the most about what dependencies are required, these will be
visible
to the proxy's ClassLoader.
If a class doesn't have an existing ClassLoader referenced by
annotatation
and cannot be resolved from the proxy's Bundle, it probably requres
a new
bundle to be resolved.
What's next? Determine what annotations to retrieve from OSGi Bundles.
How PreferredClassProvider currently obtains codebase annotations
(Trivia:
the application/system ClassLoader is a URLClassLoader up to Java 8,
but is
no longer an instance of URLClassLoader in Java 9):
Summary, If ClassLoader:
1. Is local loader? return java.rmi.server.codebase property or null
if not defined.
2. Is instance of ClassAnnoation, get annotation and return.
3. Is instance of URLClassLoader, get URL's as string and return.
4. else return java.rmi.server.codebase property or null if not
defined.
/**
* Returns the annotation string for the specified class loader
* (possibly null). If check is true and the annotation would be
* determined from an invocation of URLClassLoader.getURLs() on
* the loader, only return the true annotation if the current
* security context has permission to connect to all of the URLs.
**/
private String getLoaderAnnotation(ClassLoader loader, boolean
check)
{
if (isLocalLoader(loader)) {
return getClassAnnotation(loader);
}
/*
* Get the codebase URL path for the class loader, if it supports
* such a notion (i.e., if it is a URLClassLoader or subclass).
*/
String annotation = null;
if (loader instanceof ClassAnnotation) {
/*
* If the class loader is one of our RMI class loaders, we
have
* already computed the class annotation string, and no
* permissions are required to know the URLs.
*/
annotation = ((ClassAnnotation) loader).getClassAnnotation();
} else if (loader instanceof java.net.URLClassLoader) {
try {
URL[] urls = ((java.net.URLClassLoader) loader).getURLs();
if (urls != null) {
if (check) {
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
Permissions perms = new Permissions();
for (int i = 0; i< urls.length; i++) {
Permission p =
urls[i].openConnection().getPermission();
if (p != null) {
if (!perms.implies(p)) {
sm.checkPermission(p);
perms.add(p);
}
}
}
}
}
annotation = PreferredClassLoader.urlsToPath(urls);
}
} catch (SecurityException e) {
/*
* If access was denied to the knowledge of the class
* loader's URLs, fall back to the default behavior.
*/
} catch (IOException e) {
/*
* This shouldn't happen, although it is declared to be
* thrown by openConnection() and getPermission(). If it
* does happen, forget about this class loader's URLs and
* fall back to the default behavior.
*/
}
}
if (annotation != null) {
return annotation;
} else {
return getClassAnnotation(loader);
}
}
/**
* Returns the annotation string for the specified class loader.
*
*<p>This method is invoked in order to determine the annotation
* string for the system class loader, an ancestor of the system
* class loader, any class loader that is not an instance of
* {@link ClassAnnotation} or {@link URLClassLoader}, or (for an
* invocation of {@link #getClassAnnotation(Class)
* getClassAnnotation(Class)}) a<code>URLClassLoader</code> for
* which the current security context does not have the
* permissions necessary to connect to all of its URLs.
*
*<p><code>PreferredClassProvider</code> implements this method
* as follows:
*
*<p>This method returns the value of the system property
*<code>"java.rmi.server.codebase"</code> (or possibly an earlier
* cached value).
*
* @param loader the class loader to obtain the annotation string
* for
*
* @return the annotation string for the class loader, or
*<code>null</code>
**/
protected String getClassAnnotation(ClassLoader loader) {
checkInitialized();
return codebaseProperty;
}
Gregg
On Jan 20, 2017, at 6:08 PM, Peter<j...@zeus.net.au> wrote:
Looking at your modifications to ServiceDiscoveryManager, I noticed
you've made changes to set the context ClassLoader prior to
calling the
lookup service.
This is eventually utilised by PreferredClassProvider to lookup the
necessary loader to utilise for deserialization of the lookup
results.
I think if we develop a RMIClassLoader provider for OSGi, we can
avoid
utilising the context ClassLoader.
Since all OSGi ClassLoader's are instances of BundleReference,
it's easy
to utilise OSGi bundle url anotations (I think this needs to
incorporate
bundle versions). I'd also like to utilise Java 9 jrt style URL's.
Cheers,
Peter.
On 20/01/2017 11:09 PM, Bharath Kumar wrote:
Thanks Peter for the review.
While creating this POC, I tried to make RIO framework as set of
OSGI.
bundles. Rio project extends LookupDiscoveryManager class in one
of the
class .org.rioproject.impl.client.DiscoveryManagementPool.SharedDi
scoveryManager.
That's why I removed the final modifier.
Regarding groovy files,
I have made the org.apache.river as system fragment bundle. So we
can't
import any packages from other bundles. But we can use system
bundle's
packages,. That's why i removed groovy files. If we use these groovy
files,
we need to import packages from groovy bundle which is not possible
here. I
will check JGDMS to see how it is used.
Thanks& Regards,
Bharath
On Fri, Jan 20, 2017 at 6:09 PM, Peter<j...@zeus.net.au> wrote:
Hi Bharath,
Re your changes (I've found so far):
LookupDiscoveryManager is non final, I'm interested why?
BasicInvocationDispatcher, you've set the context class loader
around a
block of code, to use the ClassLoader passed in during
construction.
I'm
currently investigating addong methods where ClassLoader can be
passed
in
for OSGi.
Regarding bundle structure, I've restructured the layout here
(so you
don't need to delete Groovy config):
https://github.com/pfirmstone/JGDMS/tree/Maven_build/modularize/JGDMS
The full commit history has been retained, so u can see all
changes.
Cheers,
Peter.
Sent from my Samsung device.
Include original message
---- Original message ----
From: Bharath Kumar<bharathkuma...@gmail.com>
Sent: 20/01/2017 09:42:38 pm
To: dev@river.apache.org
Subject: Re: OSGi
Hello all,
I have also added a package in org.apache.river bundle to create
the
river
service in osgi environment ( Here RIver
uses NonActivatableServiceDescriptor).
package name is org.apache.river.start.ext
As river bundle is system fragment, i have to remove
the groovy dependency.
So i removed groovy files.
net.jini.config.Component.groovy
net.jini.config.GroovyConfig.groovy
Thanks& Regards,
Bharath
