Is it possible to dlopen the running executable (for purposes of classloading)

Sage

Posts: 1,199
Joined: 2004.10

Post: #1

Sep 6, 2005 — 04:08 AM

I have a hacky C++ classloader -- which is to say, I have a simplistic mechanism where I've mapped classnames to factory functions. Such that I can call:

Code:

Factory::instance()->create( "SkyDome" );

And that's great. But, for the factory to work, I've got to define a factory function ( just a function which returns a new instance of a certain class ), and I've got to register it with the factory class, as such:

Code:

Factory *f = Factory::instance();

f->registerFactory( "SkyDome", SkyDome_create );

f->registerFactory( "CelestialBody", CelestialBody_create );

f->registerFactory( "Terrain", Terrain_create );

//...

// and so on, and so on. Ad nauseam.

So I was thinking, what if I dlopen'ed my running executable and attempted to dlsym the factory function? I know darwin doesn't have a dlopen, but the dlcompat library has worked for me to "simulate" dlopen quite effectively.

The problem is, I get a dlerror() message that the file ( the running executable ) is not a library. Which I suppose is true. But I *know* I've seen configure scripts output "yes" for "executable can dlopen itself".

Here's the project ( it includes dlcompat )
http://zakariya.net/shamyl/ClassLoader.zip

Can anybody help me figure out how to make this work? Perhaps I need to use something closer to Darwin to open and resolve symbols in an executable ( as opposed to a library)? Perhaps there's some magic gcc param which will suddenly allow my app to be considered "dlopenable"?

Thanks,

TomorrowPlusX

Sage

Posts: 1,199
Joined: 2004.10

Post: #2

Sep 7, 2005 — 07:29 AM

So, thanks to help from the darwin mailing list, I got it working using CFBundle. In fact, the code's *super* simple.

My question now, since I've generally avoided c macros like the plage, is how to make a macro along the lines of the following work:

Code:

#define FACTORY(cname) extern "C" ClassLoadable *cname_create(void){ return new cname; }

Such that in my code I could define a class as such:

Code:

class Foo : public ClassLoadable

{

    public:

        Foo( void );

        virtual ~Foo( void );

        // and so on

};

FACTORY(Foo);

What I want is for this to expand to:

Code:

extern "C" ClassLoadable *Foo_create( void ) { return new Foo; }

But what it actually expands to is:

Code:

extern "C" ClassLoadable cname_create( void ) { return new Foo; }

Can any macro wizards here help me out?

TomorrowPlusX

Sage

Posts: 1,199
Joined: 2004.10

Post: #3

Sep 7, 2005 — 08:02 AM

If this a valid approach? It seems to work, but it leaves me feeling a little iffy.

Code:

#define _create

#define FACTORY(cname) extern "C" ClassLoadable * cname##_create(void){ return new cname; }

#undef _create

Like I said, it works, but I'm a little uncertain. Any thoughts?

NCarter

Moderator

Posts: 365
Joined: 2002.04

Post: #4

Sep 7, 2005 — 08:15 AM

I couldn't say if that works without trying it, but the '##' concatenation operator is definitely what you want. Check out this page, for example.

Neil Carter
Nether - Mac games and comic art

TomorrowPlusX

Sage

Posts: 1,199
Joined: 2004.10

Post: #5

Sep 7, 2005 — 10:43 AM

Excellent! I can now get rid of my spurious #define _create. THanks for the link, I googled quite a bit for C macro info, but didn't stumble across that *very* useful page.

Thanks,

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