[boost] Re: DLL/SO loading library.

From: Vladimir Prus (ghost_at_[hidden])
Date: 2005-04-27 05:43:29

Vladislav Lazarenko wrote:

> Vladimir Prus wrote:
>> I have some initial work in boost sandbox, directory libs/plugin.
>> However, I'm more interested in higher-level functionality -- given a
>> shared library create an instance of class defined there, given name of
>> the class and a set of constructor arguments.
>> 
>> - Volodya
>> 
> 
> Hm.. it will aplly some dependensies to shared library development. I mean
> it is impossible for example to get a set of constructor argument of the
> class stored in the shared library without shared library development
> agreement. So, if we want to go this way then we need to define some base
> interface for the class and all of the classes in SO/DLL should implement
> it. 

Sure. I doubt there are many use case where you can use a symbol in a DLL
knowing only its name ;-)

> Moreone, for class X we should have some description struct which will 
> have information about that class (at least class type), a pointer to the
> function which will create an instance of the class, information about
> arguments (possible with its description), pointer to the function which
> creates an instance of that class (Class *createInstance(...)). And also a
> list of exported classes (extern "C" struct with a list of description
> structs), init and fini methods (to hide DLLMain/_init/_fini from the
> user).
> 
> Am I right?

Yes. In my design shared library keeps a map<string, any>. When you want to
create a plugin, you specify a name and a base type. That map is accessed
for and the 'any' value, if found, is cast to
'abstract_factory<BasePluginType>' and then a 'create' method of
'abstract_factory' is called. For each base plugin type, you specialize a
template class called 'virtual_constructors', which specifies all
constructor signatures you may use when creating plugins of those types.
So, abstract_factory<BasePluginType> will have one 'create' overload for
each signature.

The information about arguments is not represented at run-time, as I can get
everything to work with static type information.

- Volodya