It would be pretty difficult to write threaded code for Windows in 1989, since it didn't support threads until WinNT 3.1 (1993).
But even in late 90s it was still common for desktop Win9x apps to use the main window message loop for async processing (Win32 API itself heavily encouraged it at the time - e.g. that's how OS timers work) in lieu of threads.
But even in late 90s it was still common for desktop Win9x apps to use the main window message loop for async processing (Win32 API itself heavily encouraged it at the time - e.g. that's how OS timers work) in lieu of threads.