OSGi Community Event 2012

1. Motivation
Implementation
Going Universal
Summary
Universal Declarative Services
A component framework for C++ and a model-driven solution to
polyglot components
Simon Chemouil
1
1Global Vision Systems
OSGi Community Event, 2012
Simon Chemouil Universal Declarative Services

2. 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
Simon Chemouil Universal Declarative Services

3. 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
Simon Chemouil Universal Declarative Services

4. Motivation
Implementation
Going Universal
Summary
Why modularity?
Service Components
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.
Simon Chemouil Universal Declarative Services

5. Motivation
Implementation
Going Universal
Summary
Why modularity?
Service Components
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
Simon Chemouil Universal Declarative Services

6. Motivation
Implementation
Going Universal
Summary
Why modularity?
Service Components
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!
Simon Chemouil Universal Declarative Services

7. Motivation
Implementation
Going Universal
Summary
Why modularity?
Service Components
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!
Simon Chemouil Universal Declarative Services

8. Motivation
Implementation
Going Universal
Summary
Why modularity?
Service Components
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?
Simon Chemouil Universal Declarative Services

9. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
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!
Simon Chemouil Universal Declarative Services

10. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
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
Simon Chemouil Universal Declarative Services

11. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
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.
Simon Chemouil Universal Declarative Services

12. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
Component Descriptions in C++
Denition
class C o m p o n e n t D e s c r i p t o r {
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 omponent Reference ∗ r e f e r e n c e s ;
const bool i m m e d i a t e ;
const bool a u t o E n a b l e ;
} ;
Simon Chemouil Universal Declarative Services

13. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
Component Descriptions in C++
Let's see how it looks like in practice. . .
Simon Chemouil Universal Declarative Services

14. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
Extensible Hello World!
Simon Chemouil Universal Declarative Services

15. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
Component Descriptions in C++
Denition
std : : vector ComponentReference ∗ r e f e r e n c e s = . . . ;
references −push_back (
ComponentReference (greetdemo : : GreetProvider ,
greetdemo : : GreetProvider ,
std : : s t r i n g () , ComponentReference : : DYNAMIC,
ComponentReference : : MULTIPLE,
ComponentReference : : OPTIONAL_REF) ) ;
std : : vector std : : string s e r v i c e s ;
s e r v i c e s . push_back (greetdemo : : GreetManager) ;
ComponentDescriptor ∗ componentDesc =
new ds4cpp : : ComponentDescriptor (
greetdemo : : GreetManagerImpl , ,
s e r v i c e s , ∗ references , true , true ) ;
Simon Chemouil Universal Declarative Services

16. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
A Component in C++
Denition
c l a s s GreetManagerImpl : p u b l i c GreetManager {
p u b l i c :
GreetManagerImpl () ; v i r t u a l ~GreetManagerImpl () ;
void a c t i v a t e () ;
void addGreetProvider ( GreetProvider ∗) ;
void removeGreetProvider ( GreetProvider ∗) ;
// S e r v i c e m e t h o d s .
s t r i n g getDefaultTarget ( const s t r i n g ) const ;
s t r i n g getGreeting ( const s t r i n g , const s t r i n g )
const ;
l i s t string g e t A l l G r e e t i n g s ( const s t r i n g ) const ;
l i s t string getAvailableLanguages () const ;
};
Simon Chemouil Universal Declarative Services

17. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
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
Simon Chemouil Universal Declarative Services

18. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
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!
Simon Chemouil Universal Declarative Services

19. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
C Wrapper
Denition
extern C {
DS_ABI_EXPORT GreetManagerImplWrapper∗
__greetdemo__GreetManagerImpl__create () {
return new GreetManagerImplWrapper ;
}
DS_ABI_EXPORT void __greetdemo__GreetManagerImpl__activate (
GreetManagerImplWrapper∗ object ) {
object −a c t i v a t e () ;
}
DS_ABI_EXPORT void
__greetdemo__GreetManagerImpl__add_greetdemo__GreetProvider (
GreetManagerImplWrapper∗ object , : : us : : Base ∗ s e r v i c e ) {
greetdemo : : GreetProvider ∗ l s e r v i c e = dynamic_castgreetdemo : :
GreetProvider ∗( s e r v i c e ) ;
object −addGreetProvider ( l s e r v i c e ) ;
}
DS_ABI_EXPORT void
__greetdemo__GreetManagerImpl__remove_greetdemo__GreetProvider (
GreetManagerImplWrapper∗ object , : : us : : Base ∗ s e r v i c e ) {
greetdemo : : GreetProvider ∗ l s e r v i c e = dynamic_castgreetdemo : :
GreetProvider ∗( s e r v i c e ) ;
object −removeGreetProvider ( l s e r v i c e ) ;
} } // extern C
Simon Chemouil Universal Declarative Services

20. Motivation
Implementation
Going Universal
Summary
Challenges in C++
Dening components
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?
Simon Chemouil Universal Declarative Services

21. Demo Time!

22. Motivation
Implementation
Going Universal
Summary
Simpler Component Denitions
What's next?
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.
Simon Chemouil Universal Declarative Services

23. Motivation
Implementation
Going Universal
Summary
Simpler Component Denitions
What's next?
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 {
g r e e t d e m o . G r e e t M a n a g e r
}
references {
dynamic service g r e e t d e m o . G r e e t P r o v i d e r [ 0 . . n ]
}
}
Simon Chemouil Universal Declarative Services

24. Motivation
Implementation
Going Universal
Summary
Simpler Component Denitions
What's next?
Dening multiple components
Denition
module DSDemo {
name = DS G r e e t Demo
version = 1 . 0 . 0
includes {
g r e e t d e m o . E n g l i s h G r e e t P r o v i d e r
g r e e t d e m o . F r e n c h G r e e t P r o v i d e r
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
g r e e t d e m o . C o n s o l e G r e e t e r
}
}
Simon Chemouil Universal Declarative Services

25. Generating C++ code

26. Demo Time!

27. Motivation
Implementation
Going Universal
Summary
Simpler Component Denitions
What's next?
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
Simon Chemouil Universal Declarative Services

28. Motivation
Implementation
Going Universal
Summary
Simpler Component Denitions
What's next?
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
Simon Chemouil Universal Declarative Services

29. Motivation
Implementation
Going Universal
Summary
Simpler Component Denitions
What's next?
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!
Simon Chemouil Universal Declarative Services

30. Motivation
Implementation
Going Universal
Summary
Conclusion
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!)
Simon Chemouil Universal Declarative Services

31. Motivation
Implementation
Going Universal
Summary
Conclusion
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.
Simon Chemouil Universal Declarative Services

32. Motivation
Implementation
Going Universal
Summary
Conclusion
Universal Declarative Services
Questions?
Twitter:
@simach
simon.chemouil@global-vision-systems.com
Simon Chemouil Universal Declarative Services