[vtkusers] Modified() on PolyData if PolyDataReader started in a different thread

[Sophonet]

Hi list,

in an application, I am reading vtkPolyData from file (using 
vtkPolyDataReader), but I am doing this in a separate thread (started 
with C++11 std::async()) such that loading the data does not block the 
UI. The rest of the rendering pipeline is set up in the main thread, 
only reading takes place in a worker thread.

Strangely, when I modify Points in that mesh (in the main thread) via 
SetPoint() later and call Modify(), the changes are not mapped to the 
renderwindow after calling Render().

If I read the data in the main thread, the problem does not occur, i.e. 
the Modify() call indeed leads to mapping the changes to the window.

What do I need to call in the main thread, after retrieving the data 
from the future<> with get() such that the Modify() mechanism works?

Thanks,

Sophonet