From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-07-28 01:12:53
Ben Young wrote:
> On Tuesday 27 July 2004 07:21, Vladimir Prus wrote:
> > Do you mean that reference counting should be done by DLL itself? Why
> > not:
> >
> > template<class T>
> > class plugin_ptr
> > {
> > public:
> > // operator-> and friends
> > private:
> > T* m_ptr;
> > shared_ptr<dll_handle> m_dll;
> > }
> >
> > So, 'dll' won't be deleted until all plugins which use it are dead.
>
> The way we do that at my company is that all objects returned by a plugin
> are held my a shared_ptr which has a custom deleter which decrements a ref
> count on the library itself.
Something like
void* h = dlopen(......) ;
boost::shared_ptr<Plugin> p( ...... dlsym(.....),
bind(dlclose, h))
? That's interesting, but is raises two questions:
- What if you get two plugins from the same dll?
- If dll can be reloaded, then, as I mention in another email, we'd need to
notify all 'plugin_map' instances when dll is reloaded, so dll_handle must be
a bit more smart.
What I'm thinking about now is:
class dll_handle : boost::noncopyable {
public:
// Opens the specified library. If it's already opened, returns
// pointer to an existing dll_handle.
shared_ptr<dll_handle> get(const std::string& name);
void* operator[](const std::string& symbol_name);
private:
dll_handle(const std::string& name);
};
class dll {
public:
dll(const std::string& name);
// default copy-ctor is OK
template<.......>
.... call(.......);
template<......>
.... import(.......);
private:
boost::shared_ptr<dll_handle> m_handle;
};
class plugin_ptr {
public:
// Minimum set of smart_ptr methods
private:
// Just to keep the DLL in memory when plugin is in memory
shared_ptr<dll_handle> m_handle;
};
class plugin_map {
public:
... interface to be yet defined ...
};
- Volodya