On 13 June 2015 at 16:00, Gabriel Marcano <gabemarcano@xxxxxxxxx> wrote: > > >> I don't see any way to avoid this, you're taking a pointer to code > >> defined in the shared library, then unloading the shared library, then >> using the code that was just unloaded. > > > > That's what I figured was happening. I do find it a bit strange that the > function needs to be called at destruction. I've been looking through the > source code for libstdc++ trying to figure out what's happening at a lower > level, and I'm actually a bit more confused. > > In particular, I'm confused by the fact that _M_manager itself is causing > the segfault. Looking at the library code, > >> Manager_type _M_manager; >> ... > >> typedef bool (*_Manager_type)(_Any_data&, const _Any_data&, >> _Manager_operation); > > _M_manager seems to be a function pointer to a specific type of management > code. The segfault is happening because whatever _M_manager was, it was > > invalidated. It seems _M_manager is set somewhere deep in the code. From > what I can tell, _M_manager is set to something in shared.cpp, some > internal pointer defined by _Function_base::_M_manager. There is also > some sort of inheritance going on, but at the end of the day the core of > the handler function seems to be the one defined by > > _Function_base::_M_manager. Why is accessing this function causing a > segfault? As far as I can trace with GDB my function is NOT being called > at destruction, so it's not the one to blame for the segfault. Unless I'm > misunderstanding something? Read my answer again, I already explained that. When you do "fun = shared" you instantiate a function template. The instantiation is in your shared library. The address of that instantiation is assigned to fun._M_manager When you unload the shared library that address becomes invalid. In the destructor the manager function is called to free the resources held by the std::function. You can do "f = nullptr;" before unloading the library to force the resources to be freed first, and the manager function set to null before it becomes invalid.
