What can Services do under Windows?

Question

Does anyone have a good guide to capabilities of Windows Services under XP? In particular, I am trying to find out what happens when a program being run as a service tries t

Answer 1

A service in Windows XP can interact with the Desktop if its "Allow Service to Interact with Desktop" property (MMC -> service properties -> Log On tab) is checked. It is also possible to do so by doing the following:

hWinstation = OpenWindowStation("winsta0", FALSE, MAXIMUM_ALLOWED);
SetProcessWindowStation(hWinstation);
hDesktop = OpenDesktop("default", 0, FALSE, MAXIMUM_ALLOWED);
SetThreadDesktop(hDesk);

But be aware that presenting UI from a service process in Windows XP will almost always lead to a security problem (see Shatter attack). You should try to break out the UI part of your application from the service.