I hereby extend a public THANK YOU to Gregg for this excellent patch,
and to recommend that it be accepted into River. With this patch
(actually, a slightly trimmed down version of it), I am successfully
running a River service from inside an OSGi container (Equinox) for the
first time with my custom RMIClassLoaderSpi implementation.
Chris
-----Original Message-----
From: Gregg Wonderly [mailto:[email protected]]
Sent: Friday, April 02, 2010 12:31 AM
To: [email protected]
Subject: Re: [jira] Updated: (RIVER-336) Jini should support platforms
other than those with RMIClassLoader as the classloading control point.
IDEs inparticular need help.
There are two primary issues that I needed to deal with for netbeans.
First, because netbeans is an application with a native launcher, and
all kinds
of things about it, as a platform, are private, I had problems getting
the
RMIClassLoaderSPI in River, PerferredClassProvider, to even activate.
There was
an issue of having to copy the jars into a private directory. That
wasn't
something that felt like a production step, and it would not make it
possible to
install and use a plugin supporting river without restarting the IDE.
This
seemed a bit fragile if not just ugly.
Second, the simple implementation of PreferredClassLoader creation in
net.jini.loader just uses the system classloader as the "parent" for the
created
class loader. In netbeans, the class loader hierachy that a module
sees, is
just the module and its dependents, with the parent of that loader being
the
system class loader. The netbeans system class loader is nearly empty.
It just
has the bootstrap of netbeans visible, and then netbeans creates
compartmentalized views of various modules as it loads things. So, when
I
finally got PreferredClassProvider activated, downloaded jars could not
find
stuff that was "platform" in the since that the module had this stuff in
its
classloader. That module classloader was not visible because the
PreferredClassLoader's parent was just the netbeans startup jars and the
JRE.
Thus, I really had a hard time making net.jini.loader work as it
existed. I
looked around and saw that there are actually very few places that
RMIClassLoaderSPI et.al. is used, and that all of those places where of
interest
to me in how I could make Jini work inside of netbeans (at least I
hoped).
So, I decided to just put a layer of indirection (what programmers do to
solve
most problems :-) between net.jini.loader and RMIClassLoaderSPI that
would allow
the mechanism itself to be supplanted.
So, these patches allow one to override how all of the RMIClassLoaderSPI
mechanisms are implemented, plus adding some twists specifically about
how the
"parent" classloader is chosen for PreferredClassLoader instances.
And, to top it off, some of you may recall that I modified preferred
class
loading to actually have the facility to "never prefer" some classes.
What this
meant was that jar files in the codebase would never be downloaded and
thus in
large, distributed systems, with lots of jars visible across slow
networks, a
ServiceUI client application could startup, and show all visible
services,
without downloading anything.
Additionally, I also make changes to Reggie to return marshalled data
values so
that unmarshalling would not occur, which would trigger downloads.
By making these changes, I was able to move the "never prefer"
implementation
into my CodebaseClassAccess implementation so that it becomes a feature
for me,
not a platform implementation detail.
Please ask questions if I've not provided enough details somewhere.
Gregg Wonderly
Christopher Dolan wrote:
Gregg,
This patch is interesting to me.
The implementation is clear: create a new plugin point to override the
default RMIClassLoader. Could you explain the motivation a little
more?
It seems like the intention is to make River play nice in a large
process by not insisting that the global RMIClassLoader be configured
to
suit River. And it looks like it is fully backward compatible for
River
deployments that are already overriding RMIClassLoader by defaulting
to
RMIClassLoaderCodebaseAccess.
If nothing else, I would love to use something like this just to
reduce
the huge number of places where I have to include
"-Djava.rmi.server.RMIClassLoaderSpi=...". That alone would be a win.
Or am I reading too much into this?
Chris
-----Original Message-----
From: Peter Firmstone [mailto:[email protected]]
Sent: Thursday, April 01, 2010 4:16 AM
To: [email protected]
Subject: Re: [jira] Updated: (RIVER-336) Jini should support platforms
other than those with RMIClassLoader as the classloading control
point.
IDEs inparticular need help.
Should I create a branch on svn for this?
Regards,
Peter.
Gregg Wonderly (JIRA) wrote:
[
https://issues.apache.org/jira/browse/RIVER-336?page=com.atlassian.jira.
plugin.system.issuetabpanels:all-tabpanel ]
Gregg Wonderly updated RIVER-336:
---------------------------------
Attachment: rmicl.diff.txt
This is a diff out of my perforce node for the affected classes that
I've been using for some time. The changes shown here are
preliminary
and should be considered experimental.
Jini should support platforms other than those with RMIClassLoader
as
the classloading control point. IDEs inparticular need help.
------------------------------------------------------------------------
-----------------------------------------------------------
Key: RIVER-336
URL: https://issues.apache.org/jira/browse/RIVER-336
Project: River
Issue Type: New Feature
Components: net_jini_loader
Affects Versions: AR3
Reporter: Gregg Wonderly
Attachments: rmicl.diff.txt
The RMIClassLoader class and RMIClassLoaderSPI is currently the
control point for managing the "platform" view of how classes are
loaded. In IDEs and other different environments, the "parent"
classloader view, is not always the "system class loader". There are
some other variations on class loading that seem to indicate that
while
RMIClassLoaderSPI can be plugged into, it doesn't always provide quite
the right facilities because even plugging into the system class
loader
to override it might not be possible.
The diffs included here show some preliminary work that I did
investigating this issue to try and make it possible to discover and
load Jini servers within the netbeans IDE.
Refinement and some rework will be needed, and some other
investigation into other platforms such as JEE and other IDEs would be
helpful in making sure we understand what is really needed. Even OSGi
would be something to look at.
