Re: [Boost-users] [Serialization] Serializing classes defined in DLLs

From: Robert Ramey (ramey_at_[hidden])
Date: 2005-09-16 17:42:26

I know people have been doing this.  But I also know there have been issues 
with the dynamic loading and unloading of modules which contain 
serialization code.  I really need a good small test program to be added to 
my test suite.

I would expect the following to work;  Your example isn't realy complete 
enough for me to comment on.

Robert Ramey

Topi Mäenpää wrote:
> Hi,
>
> How do I register classes that are defined in a dynamically loaded
> so/dll? Using BOOST_CLASS_EXPORT just causes "terminate called after
> throwing an instance of 'boost::archive::archive_exception'
>   what():  unregistered void cast". My set-up is as follows:
>
> class A {
> public:
>   A();
>   virtual ~A() {}
> private:
>   // polymorphic archive stuff here
> };
>
> class B : public A {}
>
> BOOST_CLASS_EXPORT(B);
>
>
> Serializing instances of B through a A* works fine if B is defined in
> the main executable. Now, I have tried the following (approximately):
>
> // An exported function that returns a void pointer
> typedef void* (*func)();
>
> int main()
> {
>   // Load a dynamic library
>   dll lib = load_dll("mylib.dll");
>   // Get a pointer to the instance creator function
>   func instance_creator = (func)lib.resolve("instance_creator");
>   // An instance of B is created in the dll and returned as a void*.
>   A* a = (A*)instance_creator();
>
>   ...
>
>   archive & a; //throws unregistered void cast
> }
>
> B is both defined and exported in mylib.dll.
>
> So, what is the deal? I don't understand the soul of
> BOOST_CLASS_EXPORT well enough to solve the problem myself. But since
> I'm using the dll version of the serialization library, I'd assume
> that the dynamically loaded dll (mylib.dll) and the main executable
> use the same address space for the archive classes. I would
> understand this if I encountered this problem with static linking
> because I'd need to inlude two copies of the serialization library...
>
> Any advice?
>
> Regards,
> Topi