[paragui-users] the dll low down

[Keith Swyer]

ok, i'll geive you some nice details.....

- i am using a base class that all the dlls are based from

class Area{
public:
    virtual void FillArea(void *data, void *data2) = 0;
private:
    friend class dll_object_ref<Area>;
    virtual void destroy()=0;
};

- in the dlls i create i use the Area base class, then call a macro
FACTORY_ENTRY(newclass, name)
which then calls this....  allowing us to have a clean way to access the
names without the c++ mangled crap.
(externc is a macro for extern "c" and dllfunc is just the export )
#define FACTORYFUNC( base , the_class , prefix , classid ) \
  EXTERNC DLLFUNC base* DLLCALL prefix##classid( void )    \
    { return new the_class; }

- these are the DLL support classes: dll_sentinel, dll_object_ref, and
dll_object_ptr.
Class dll_sentinel is responsible for ensuring that the DLL is resident
during the sentinel's lifetime. It keeps track of both the DLL name and the
handle to that DLL. The first time a dll_sentinel is created, it asks the OS
to load the DLL, and the OS sets the DLL's reference count to one. Every
time another dll_sentinel loads the same DLL, the OS increments that DLL's
reference count. When each dll_sentinel is destroyed, it asks the OS to
close the DLL. The OS actually just decrements the DLL's reference count,
and unloads the DLL only when that count reaches zero.
dll_object_ref contains a dll_sentinel, a pointer to an object residing in
the DLL, and a reference count. When a dll_object_ref is constructed, it
finds the appropriate function in the DLL and uses it to initialize its
pointer. When the dll_object_ref is destroyed, it deletes the object pointed
to.

dll_object_ptr is similar to std::auto_ptr, except that its ownership
semantics are slightly different. Copying one dll_object_ptr to another does
not cause one of them to become invalidated or to lose ownership of the
underlying object. Because dll_object_ptr takes advantage of
dll_object_ref's reference counting scheme, the underlying object gets
destroyed only when all of its dll_object_ptrs are destroyed.

Now that i hopefully have you all confused  :)  i don't have a way that each
dll instanciates themselves automatically yet, but right now my factory
template allows you to instantiate by referring to the name of the
class.....anyway, this all works fine and i can call _object->FillArea
fine, but inside of that function in the dll i cannot use any of the paragui
functions.



well, i hope this isn't too much to wrap your heads around as i know i'm
getting a litte off paragui specific (but i am planing to add this somehow
to pg) any help would be great. I know this isn't probably the best way to
do what i'm doing, but i've had to figure this all out by looking around the
net, and i'm only new to using and making dlls...   :)



--Keith