Hi Kumar,
> Do you think this will work out ?
It can work. It won't be fun.
> One other aspect I am concerned about is that with the above, myprog will eventually make use of both the gcc C++ runtime and the Sun C++ runtime (via the two MODULES A and B which respectively call into libs libA.so and libB.so). Do you see any issues with that ?
The key issue is making sure that symbols are properly bound, such that the Sun C++ only binds to Sun C++ symbols by the loader, and GCC C++ only binds to GCC C++ symbols by the loader.
Another solution is to use separate processes, and then communicate to the Sun C++ "slave" process (assuming that's the one you'd make slave) through RPC or IPC or a listening socket. That makes for a very clean demarcation between the GCC C++ process and the Sun C++ process.
> Also - do you know of any good examples and/or web resources that demonstrate how the "thunking" libs. should be created and provide more info. on the details ?
No, I'm not sure.
I learned it by working with Netwise RPC technology, before Microsoft acquired them.
Another good example of providing an opaque C interface to an object-oriented implementation is Apple's Carbon. X11 is also a good example of object-oriented design, implemented in C (which could have been written in C++ -- maybe it is in some implementations).
If you only have one top level class to expose, say SunFoo...
class SunFoo
{
public:
SunFoo();
~SunFoo();
void DoSomething();
void OtherSomething(std::string const&);
};
...you're thunking C interface will have to provide...
Initialize();
Terminate();
int ExceptionOccurred();
typedef struct OpaqueSunFoo* SunFoo_t;
SunFoo_t SunFooConstruct();
void SunFooDestruct(SunFoo_t);
void SunFooDoSomething(SunFoo_t);
void SunFooOtherSomething(SunFoo_t, char const*);
You'll need to have a "cookie" that represents a SunFoo on the GCC side. Something like "typedef struct OpaqueSunFoo* SunFoo_t" can work well.
You'll need to "revive" all C-style parms into the SunFoo's C++ object parms.
You'll need to carefully manage memory allocation so the right side of the fence has ownership & responsibility to delete/free things.
You'll need to catch all exceptions and have some facility to query if an exception occurred.
If your Sun C++ has lots and lots of objects and methods that you want to expose... then that can be a considerable (and very unpleasant) challenge.
HTH,
--Eljay
