Hi Folks,
Currently with Eclipse EASE it's easy :) to script Eclipse with
Python. What's not currently as easy to do is:
1) Allow python code to access/call OSGi services
2) Allow java code to discover and call python-based services
(without an explicitly registered listener)
3) Support the dynamics of OSGi services (services come and go
at runtime, binding by DS or Spring, etc)
I've recently been working on a thing I call a 'service bridge'
[1] that using Py4j it bridges Python with the OSGi service
registry. It does this by creating a Py4j-based distribution
provider for ECF's implementation of OSGi Remote Services [2].
The service bridge enables all three of the above, and does it
in a standards-based (RSA) way. For example, for 2 let's say
we have a python class:
class EvalProvider(object):
def eval(self, _expression_):
'parse _expression_, evaluate (parse function above) and return as float/Double'
return float(parse(_expression_))
class Java:
implements = ['com.acme.prime.eval.api.Eval']
with the Py4jServiceBridge we make the following call:
Py4jServiceBridge.export(new EvalProvider(),rsaProps)
and on the java side a proxy will be created (with all the OSGi
classloading restrictions taken care of) and dynamically
registered in the OSGi service registry...meaning that consumers
of the com.acme.prime.eval.api.Eval service will have this
instance injected and can use it:
@Reference(policy=ReferencePolicy.DYNAMIC)
void bindEval(Eval svc) {
System.out.println("EvalConsumer
returns="+svc.eval("21+21"));
}
Here's the java-side service Eval service interface:
public interface Eval {
double eval(String _expression_) throws Exception;
}
and the Python eval _expression_ will be called...and can execute
arbitrary Python code (any Python impl). This will work
similarly for any service (not just Eval :). There is nothing
on either side that requires service consumers to care that the
implementation is provided by Python (or Java). If necessary
it can be figured out, but consumers are not required to write
any custom code, making it easy to switch between languages for
service impls and even distribution systems (e.g. switching to
xmlrpc, rest, hazelcast, or some other network distribution
provider [3]).
All the dynamics are supported without app-level code...e.g.
services come and go at runtime, are cleaned up on shutdown,
multi-threaded access, etc thanks to RSA.
Conversely, if a service is registered in java/Eclipse (any
method...via DS, registerService, etc), on the python side it
can be configured so that a listener will be dynamically called
to inject the service into python code.
I'm trying to determine how to contribute this...it could be
through ECF, EASE, January, new project, or other. One thing
to mention: it's only dependent on OSGi, and so will of course
work in Eclipse IDE, Che, Orion, any RCP app, as well as OSGi
servers...Karaf, Websphere and others. If you have thoughts
about how you would like to consume please LMK.
Scott
[1] https://github.com/ECF/Py4j-RemoteServicesProvider
[2]
https://wiki.eclipse.org/Eclipse_Communication_Framework_Project#OSGi_Remote_Services
[3] https://wiki.eclipse.org/Distribution_Providers
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