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From Thomas Gentsch ...@e-tge.de>
Subject Re: Porting Tuscany C++ to C++11 and some code cleanup
Date Mon, 14 Jan 2013 21:03:48 GMT
On Sun, 2013-01-13 at 23:35 -0800, Jean-Sebastien Delfino wrote:
> On Mon, Jan 7, 2013 at 1:28 PM, Thomas Gentsch <tg@e-tge.de> wrote:
>         Hello JS,
> Hi Thomas, Happy New Year!

Many thx! Same back!!

>         now, I did some more reading etc and believe now that I mostly
>         understand what's going on :-)
>         The main missing pieces were these (correct? Possibly my
>         terminology is
>         a bit fuzzy :-):
>         Q: When are SDOs used (in SCA M3) and when not?
>         A: If an interface of a service uses complex types as in/out
>         params or
>         return value, otherwise simple types (like int, bool, string)
>         are used.
>         Complex types (i.e. class instances) an XSD are passed in/out
>         as SDO
> Yes
>         Q: Is there some kind of request routing?
>         A: Local calls are resolved during OS-loader-time. One
>         component calling
>         another is written as regular C++ code which results in
>         compiled code as
>         unresolved reference that must be satisfied during runtime by
>         the target
>         component which in turn must be loaded as shared library
> No, if I remember correctly (as M3 was a long time ago,)


> wires were resolved by Composite::resolveWires, then invocation of a
> component involved CPPServiceWrapper::getServiceWrapper to load the
> component library, lookup a factory function named after the service
> name, create an instance of CPPServiceWrapper, and eventually
> executing generated code in CPPServiceWrapper::invokeService to
> dispatch the call to the target C++ component method.  

But then the wrapper and proxy must exist - either hand-written or
WSDL-generated. The CppCalculator example though has neither. I did not
verify all the others, most have WSDL as it seems.
Maybe as long everything happens within *one* lib ... ?

Actually I was thinking that its even not a bad idea to let the OS
loader (or even the linker) resolve the calls as it is probably the
fastest way possible.

But, OK, will look again :-)

> In trunk, the equivalent of invokeService is the apply function, and
> currently needs to be written by hand as scagen has not been
> maintained (but could be brought back if somebody was interested in
> maintaining it).
>         Q: What is the purpose of composite files with pure C++
>         modules?
>         A: If a composite consists only of local components all calls
>         are
>         resolved by the OS loader. In that case basically the
>         composite
>         definition file mainly states which interfaces are in which
>         shared lib
>         and in which order are the libs to be loaded.
> See above, both M3 and trunk resolve wiring dynamically.
>         Q: How are remote request handled?
>         A: Remote interfaces are described using WSDL, which must be
>         processed
>         using the tool scagen to generate a "ServiceWrapper" and a
>         "ServiceProxy" that act as client (proxy) and server (wrapper)
>         stubs.
> In M3 ServiceWrapper and ServiceProxy were generated from WSDL by
> scagen and were used for both local and remote invocations.
>         However, some things are still unclear:
>         Q: If there is nothing like request routing, how does the
>         "wiring" work
>         if the calls are actually hardcoded?
> See above.
>         Besides of these questions a few non-technical ones:
>         Q: The trunk code stream looks to me like a complete re-write.
>         With even
>         the component interfaces changing and nobody complaining I
>         guess that
>         there is nobody actually really using Tuscany SCA C++?
> I just checked M3 again and it looks that way now when we compare
> trunk in 2013 and M3 from 2006/2007. The code has evolved slowly but
> after 6 years I'm not really surprised.
>         Q: Besides of people using it, is there anybody besides you
>         working on
>         it?
> I'm not really sure. I've been the only one pushing changes to trunk
> recently. I noticed a new lightweight-sca clone branch recently but
> can't remember who created it. When I get tech questions here, in
> email or IRC, and find time, I try to answer without bothering people
> asking what they're doing with the code, so there may be more clone
> branches here or on github for example, as the code is open to anyone
> who wants to hack on it.

>         Q: To which extent are both the M3 and trunk versions
>         "stable"? M3
>         probably in the sense that nobody works on it anymore but is
>         it mostly
>         complete/usable?
> M3 has not changed since 2007. Trunk is moving slowly as I only spend
> a little spare time on it on some weekends or holidays. Complete and
> usable are subjective notions, as IMO an open-source project is not
> 'complete' as long as people are still interested in evolving it, and
> 'usable' depends on the use case.
>         Q: What about interoperability with Tuscany Java? I suppose
>         both M3 and
>         trunk are OK as long as the binding is the same (and on the
>         wire it is
>         XML or whatever anyway). Which common binding types exist?
> With M3, REST. With trunk, REST and SOAP.
>         Generally I have to admit that I liked the old implementation
>         more,
>         though this maybe caused by the new language features in trunk
>         I'm not
>         familiar with yet.
> I've worked on C++ M3, trunk and even the Java project so I can
> imagine why someone would prefer one or the other. The good thing is
> that they're here in the open and you can do what you want with the
> code, use the bits you prefer, mix them, or even contribute to
> maintain or change them to something you like, if you're interested.

True, but the real power of open-source is if the "community" jointly
works on the same thing. Of course I cannot force anybody :-)
Also, I quite like the idea of following a standard (if it is any good,
which I cannot really tell yet).

So, in theory, I could start a project, let's say "sca-oasis", based on
M3 ... originally I'd be the only one working on it, maybe others join,
maybe not. Would that then still be "Apache Tuscany"?
Maybe I'll post something in tuscany-users like "anybody using it?" ...

>         Q: With the new value/list types, if there is no relation with
>         XSD
>         anymore, can you also query information about object types,
>         e.g. which
>         properties a class shall have? This is probably not needed in
>         the SCA
>         code, but maybe in custom extensions ...
> There isn't anything in the runtime to allow you to query the types,
> but if you have an XML (or JSON) schema, and a schema library that
> you'd like to use with your types, there's no reason why you couldn't
> use that library along with SCA.
>         Also, type enforcement is not necessarily a disadvantage
>         (admittedly
>         slower though)
> I'm not sure if you're talking about validating the data exchanged
> with SCA components (which could be done with a validating proxy) or
> about generating static code from schema type definitions, but both
> approaches should work nicely along M3 or trunk (for the latter you'd
> need a generator like scagen on top of the runtime invocation
> mechanism.)

Maybe here I'm in the SDO world again ... :-) All the schema/type stuff
is nicely integrated and I don't need to directly deal with libxml2 or
so ...

Many thx again!!!

>         Many thx again + regards,
>           the
>         On Wed, 2013-01-02 at 23:49 -0800, Jean-Sebastien Delfino
>         wrote:
>         > On Sat, Dec 29, 2012 at 6:20 PM, Jean-Sebastien Delfino
>         > <jsdelfino@apache.org> wrote:
>         >         Hi all,
>         >
>         >
>         >         I had a few more offline Q&A exchanges with Thomas,
>         and
>         >         thought it'd be useful to share a summary here:
>         >
>         >
>         >         Q: In the C++ trunk, is DataObject now replaced by
>         >         tuscany::value and tuscany::list?
>         >
>         >
>         >         A: Yes
>         >
>         >
>         >
>         >
>         > BTW I just committed a number of changes I made over the
>         holidays,
>         > including some improvements to tuscany::value and
>         tuscany::list, in
>         > particular to work with lists, nested lists and trees of
>         key/value
>         > pairs (aka associations) as well as some minor improvements
>         to handle
>         > comparisons of floating point number values.
>         >
>         >
>         > - Jean-Sebastien

 Thomas Gentsch
 Römerstr. 76
 70180 Stuttgart

 Tel : (+49) 0711 - 46915652
 mobil : (+49) 0173 - 6620507
 e-mail: tg@e-tge.de

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