There are no error returns from an APC? The return type is void and the system expects the routine (whatever it is) to return: https://learn.microsoft.com/en-us

There are no error returns from an APC? The return type is void and the system expects the routine (whatever it is) to return: https://learn.microsoft.com/en-us/windows/win32/api/winnt/nc-winnt-papcfunc https://learn.microsoft.com/en-us/windows/win32/api/winnt/nc... - whichever call put the process in the alertable wait state then ends up returning early. This is a little bit like the Win32 analogue of POSIX signal handlers and EINTR, I suppose.