Low level keyboard Hook not at UI thread

Question

I want to create a good library for keyboard hook. I use a method SetWindowsHookEx and I have noticed that method hookProc, which should be called at any system KeyDown event, is not executed if the main thread of my app is bussy. I think the hook shold be made so, that the other thread would be responsible for it. Is that possible? How can I do it?

Answer 1

Microsoft help page of LowLevelKeyboardProc mentions that

If the hook procedure times out, the system passes the message to the next hook. However, on Windows 7 and later, the hook is silently removed without being called. There is no way for the application to know whether the hook is removed.

I suspect this is what’s happening to you. Your HookProc function should be extremely fast: what mine does is just pushing the key event in a std::vector. The real code is executed in another thread.