Hi Peter, I think there is a bug in your Interlocked* implementation of shared_ptr (http://www.pdimov.com/cpp/shared_count_x86_exp2.hpp). In atomic_read you have: inline long atomic_read(long volatile const & value) { return value; } I don't believe this is thread-safe. In order to make sure you're receiving the latest value, I assume you could do something like: inline long atomic_read(long volatile & value) { const int IMPOSSIBLE_VALUE = -100; return InterlockedCompareExchange(&value, IMPOSSIBLE_VALUE, IMPOSSIBLE_VALUE); } Am I missing something? Best, John -- John Torjo -- john@torjo.com Contributing editor, C/C++ Users Journal -- "Win32 GUI Generics" -- generics & GUI do mix, after all -- http://www.torjo.com/win32gui/ -- v1.4 - save_dlg - true binding of your data to UI controls! + easily add validation rules (win32gui/examples/smart_dlg)