Universal Declarative Services

Motivation
Implementation
Going Universal
Summary

Universal Declarative Services
A component framework for C++ and a model-driven solution to
polyglot components

Simon Chemouil
1

1 Global Vision Systems

OSGi Community Event, 2012

Simon Chemouil Universal Declarative Services

Motivation
Implementation
Going Universal
Summary

Who am I?

Free Software enthusiast, functional programmer, interested in
model-driven development, modularity, re-usability,
maintainability. . .

How to never have to write that piece of software again?

Technical Architect at Global Vision Systems, Toulouse

We create data visualization software for large industries (2D,
3D, tables, etc).
We do both Java and C++

Java using OSGi (Felix, iPojo) for server and client side
(Eclipse RCP and Android)
C++ to keep a fast 3D engine-agnostic manipulation layer


Motivation
Implementation
Going Universal
Summary

Outline

1 Motivation
The case for modularity
Service Components and C++

2 Implementing Declarative Services for C++
Challenges in C++
Dening components

3 Going Universal
Simpler Component Denitions
What's next?

4 Summary
Conclusion


Motivation
Implementation Why modularity?
Going Universal Service Components
Summary

Native OSGi

Did you miss Native-OSGi, Modular Software Development in
a Native world by Alexander Broekhuis and Sascha Zelzer?

Universal OSGi

an RFP and a blog post by Peter Kriens in 2007.

Apply OSGi techniques to native (C/C++) development.


Motivation
Summary

An OSGi Architect Walks in a C++ Bar...

Our C++ project going through re-architecture / refactoring

Custom-made plugin system, limited.

Plugins can't use each other

C/C++ OSGi ports:

Celix (Alexander), CppMicroServices (Sascha), SOF, CTK,
nOSGi, . . .

Yet no service component framework such as Declarative
Services


Motivation
Summary

Why a Service Component Framework?

Services: powerful primitives, unpractical programming:

Lack of structure
Dynamic

Service Components:

Structure the services
A nice semantic model to reason about dynamism

Why is there no such framework for an OSGi C++ port:

1 Technical challenges
2 It was just not done yet!


Motivation
Summary

Why Declarative Services?

Many existing component frameworks for C++

Just as there were some for Java before DS
No modularity

Simple and matured component model

A few years of personal experience

Works with POJOs (or POCOs!)

Components do not depend on the framework
Makes them testable and easily reusable!


Motivation
Summary

Does it make sense for C++?

We use C++ for performance:

Performance hit with component frameworks?

We need extensibility and customization...

Do we need modularity?

Why use dierent architecture between Java and C++?

What if we could talk about components, whatever the
implementation language?


Motivation
Implementation Challenges in C++
Going Universal Dening components
Summary

Getting started

Native OSGi implementation:

CppMicroServices is light, works with any shared library
Inspired by PojoSR
For C++!

Bundles are called Modules:

Native shared libraries: not archives.

Moving to NativeOSGi later?

Easy! Components are framework-agnostic!


Motivation
Summary

Ingredients in Declarative Services

Components are described in XML les in the bundle

Service callbacks

Dened in description
Service arrival/departure
Policy, Cardinality, Target

Component callbacks

Activation, modication, deactivation


Motivation
Summary

Component Descriptions in C++

XML descriptions. . .

We have native shared libraries, not JARs!

Instead, we register a ComponentDescriptor instance to the
ComponentManager service.

The ComponentManager service is provided by the core
Ds4Cpp framework.


Motivation
Summary


Denition

class ComponentDescriptor {
public :
const s t r i n g c o m p o n e n t I d ;
const s t r i n g i m p l S h a r e d O b j e c t ;
const v e c t o r s t r i n g ∗ p r o v i d e d S e r v i c e s ;
v e c t o r C o m p o n e n t R e f e r e n c e ∗ references ;
const bool immediate ;
const bool autoEnable ;
} ;


Motivation
Summary


Let's see how it looks like in practice. . .


Motivation
Summary

Extensible Hello World!


Motivation
Summary

Denition

s t d : : v e c t o r ComponentReference ∗ r e f e r e n c e s = . . . ;
r e f e r e n c e s −push_back (
ComponentReference ( greetdemo : : G r e e t P r o v i d e r ,
greetdemo : : G r e e t P r o v i d e r ,
s t d : : s t r i n g ( ) , ComponentReference : : DYNAMIC,
ComponentReference : : MULTIPLE ,
ComponentReference : : OPTIONAL_REF) ) ;

s t d : : v e c t o r s t d : : s t r i n g s e r v i c e s ;
s e r v i c e s . push_back ( greetdemo : : GreetManager ) ;

C o m p o n e n t D e s c r i p t o r ∗ componentDesc =
new ds4cpp : : C o m p o n e n t D e s c r i p t o r (
greetdemo : : G r e e t M a n a g e r I m p l , ,
s e r v i c e s , ∗ r e f e r e n c e s , true , true ) ;


Motivation
Summary

A Component in C++

Denition

c l a s s G r e e t M a n a g e r I m p l : p u b l i c GreetManager {
public :
G r e e t M a n a g e r I m p l ( ) ; v i r t u a l ~G r e e t M a n a g e r I m p l ( ) ;
void activate () ;
void a d d G r e e t P r o v i d e r ( G r e e t P r o v i d e r ∗) ;
void removeGreetProvider ( G r e e t P r o v i d e r ∗) ;

// Service methods .

s t r i n g g e t D e f a u l t T a r g e t ( c o n s t s t r i n g ) c o n s t ;
s t r i n g g e t G r e e t i n g ( c o n s t s t r i n g , c o n s t s t r i n g )
const ;
l i s t s t r i n g g e t A l l G r e e t i n g s ( c o n s t s t r i n g ) c o n s t ;
l i s t s t r i n g g e t A v a i l a b l e L a n g u a g e s ( ) c o n s t ;
};


Motivation
Summary

Service Callbacks in C++ (1/2)

No reection/introspection!

There are some limited libraries (e.g Reex).

C++ name mangling

We can't guess the binary name

Instead, we force a convention in the C++ component:

setRefName, unsetRefName for single dependencies
addRefName, removeRefName for multiple
dependencies


Motivation
Summary

Service Callbacks in C++ (2/2)

Our tools: dlopen/dlsym/dlclose (and Windows equivalents)

Against us: C++ name mangling

Solutions?

Reection libraries: too limited, not dynamic.
C++11 attributes (≈ Java annotations): still largely
unsupported
Qt meta-objects? Not bad!

Yet need a custom preprocessor
Still not modular (work in progress)

How about C wrappers?

Dicult to write manually, but provide universal ABI!


Motivation
Summary

C Wrapper
Denition

e x t e r n C {
DS_ABI_EXPORT GreetManagerImplWrapper ∗
__greetdemo__GreetManagerImpl__create ( ) {
r e t u r n new GreetManagerImplWrapper ;
}
DS_ABI_EXPORT void __greetdemo__GreetManagerImpl__activate (
GreetManagerImplWrapper ∗ o b j e c t ) {
o b j e c t − a c t i v a t e ( ) ;
}
DS_ABI_EXPORT void
__greetdemo__GreetManagerImpl__add_greetdemo__GreetProvider (
GreetManagerImplWrapper ∗ o b j e c t , : : us : : Base ∗ s e r v i c e ) {
greetdemo : : G r e e t P r o v i d e r ∗ l s e r v i c e = dynamic_cast greetdemo : :
G r e e t P r o v i d e r ∗ ( s e r v i c e ) ;
o b j e c t −a d d G r e e t P r o v i d e r ( l s e r v i c e ) ;
}
DS_ABI_EXPORT void
__greetdemo__GreetManagerImpl__remove_greetdemo__GreetProvider (
GreetManagerImplWrapper ∗ o b j e c t , : : us : : Base ∗ s e r v i c e ) {
greetdemo : : G r e e t P r o v i d e r ∗ l s e r v i c e = dynamic_cast greetdemo : :
G r e e t P r o v i d e r ∗ ( s e r v i c e ) ;
o b j e c t −r e m o v e G r e e t P r o v i d e r ( l s e r v i c e ) ;
} } // e x t e r n C


Motivation
Summary

It works! But. . .

The proof-of-concept is successful:

We have components wired dynamically

OSGi's patterns work nicely (yet a bit more tricky)
We support the use cases we need

Dynamic arrival, thread-safety planned but unnished, service
removal to do.

But no one would write that wrapper code!

Are there solutions to help us here?


Motivation
Implementation Simpler Component Denitions
Going Universal What's next?
Summary

C++ is too complex!

Automatically generating the wrappers?

Where to get the description?

Macros?
Parsing C++?!

Xtext

Java tooling to dene DSLs and compilers
Generates an Eclipse editor!
Uses EMF as backend, so more can be built upon.


Motivation
Summary

Back to GreetManagerImpl!

Denition

component g r e e t d e m o . G r e e t M a n a g e r I m p l {
provides {
greetdemo . GreetManager
}
references {
dynamic s e r v i c e greetdemo . G r e e t P r o v i d e r [0..n]
}
}


Motivation
Summary

Dening multiple components

Denition

module DSDemo {
name = DS G r e e t Demo
version = 1.0.0
includes {
greetdemo . E n g l i s h G r e e t P r o v i d e r
greetdemo . F r e n c h G r e e t P r o v i d e r
greetdemo . GreetManagerImpl
greetdemo . C o n s o l e G r e e t e r
}
}


Motivation
Summary

Improving our ADL

The ADL we designed maps to Declarative Services'
capabilities

What about richer component models?

Creating new target language back-ends

Java/DS, Java/iPojo
Making it extensible


Motivation
Summary

Bridging Java and C++

Using Remote OSGi Services:

An idea discussed in NativeOSGi.
We expose C++ services where we can generate a Java
interface

Use JNI/JNA bindings or network.

Basically, we bridge the two service registries!

It does sound like CORBA


Motivation
Summary

Creating UI Tools

Textual DSLs are nice...

But component diagrams are nicer!

Up-to-date component metadata is extremely useful:

Forces high-level design (round-trips between architects and
developers)
Allows code generation/rapid project bootstrapping
Static analysis (code conformance)
Can be used for SDK documentation.

Long term project!


Motivation
Implementation Conclusion
Going Universal
Summary

Declarative Services for C++

We have been using Ds4Cpp for a few months!

If you want to try it. . . you can! We just open sourced it
(Apache Software License 2.0)

https://github.com/Global-Vision-Systems/Ds4Cpp
(the demo is packaged with it)!

We need testers and eyes to x my bad C++ :-)

And remove the limitations (talk to me!)


Motivation
Going Universal
Summary

Universal Components Tooling

The tooling has still some rough edges

Enough for our current needs. . .

Some clean-up required.

We have a roadmap for the improvements.


Motivation
Going Universal
Summary

Universal Declarative Services

Questions?

Twitter:

@simach

simon.chemouil@global-vision-systems.com


Universal Declarative Services

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