C++: Error handling problem across threads

Question

In general I use exceptions to deal with errors, however the problem I have here is that the error applies to a different thread than the one that caused it.

Basicly the window has its own thread, and the direct3d device must be created and reset by the same thread that created the window. However creating the device may fail, so I need to throw an exception in the thread that was trying to create the instance, not the window code

The callback function:

void Callback(HWND hwnd, boost::function<void(HWND,LPARAM)> call, LPARAM lParam)
{
    //Make our stack allocated function object into a heap allocated one
    boost::function<void(HWND,LPARAM)> *callH = new boost::function<void(HWND,LPARAM)>(call);
    //send a message with a pointer to our function object in the WPARAM
    PostMessage(hwnd, WM_CALLBACK, (unsigned)callH, lParam);
}
LRESULT CALLBACK HookProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    //check for our custom message
    if(msg == WM_CALLBACK)
    {
        //retreive the function pointer from the WPARAM
        boost::function<void(HWND,LPARAM)> *callH = (boost::function<void(HWND,LPARAM)>*)wParam;
        //call it
        (*callH)(hwnd,lParam);
        //delete our heap allocated function object
        delete callH;
        return 0;
    }
    else
        //if there was nothing relevant to us, call the old message procedure
        return CallWindowProc(hooked[hwnd], hwnd, msg, wParam, lParam);
}
//std::map<HWND, WNDPROC> hooked;

The code that requests the window thread to create the device

Graphics::Graphics(IWindow *_window, Size2<unsigned> _size)
:lost(false), reset(false), refCnt(0), backCol(0xFF000000),
started(false), exited(false),
window(_window), size(_size)
{
    window->AddRef();
    HWND hwnd = *((HWND*)window->GetHandle());
    CallbackHook(hwnd);
    Callback(hwnd, boost::bind(&Graphics::create, this), 0);

    while(!started)Sleep(100);
}
void Graphics::create()
{
...code that may throw various exceptions
    started = true;
}

So basically I need the exceptions being thrown by the create() method to be caught by the exception handelers where the Graphics object was created which is another thread.

Answer 1

Perhaps you can wrap the call inside another function, using Boost.Exception.

The following code does not work though, but you'll probably get the idea.

class Context
{
public:
    Context(HWND hwnd, const boost::function<void(HWND,LPARAM)>& f, LPARAM lParam)
    {
        // TODO: reroute call through Wrapper function.
    }

    void wait()
    {
        mutex::scoped_lock l(m);
        while (!finished)
        {
            c.wait(l);
        }
        if (ex)
            rethrow_exception(ex);
    }

private:
    void Wrapper()
    {
        try
        {
            f(/*params*/);
        }
        catch (...)
        {
            ex = current_exception();
        }
        mutex::scoped_lock l(m);
        finished = true;
        c.notify_all();
    }

    boost::function<void(HWND,LPARAM)> f;
    exception_ptr ex;
    bool finished;
    mutex m;
    condition c;
};

void Callback(HWND hwnd, const boost::function<void(HWND,LPARAM)>& f, LPARAM lParam)
{
    Context ctx(hwnd, f, lParam);

    ctx.wait();
}