lynx-dev Using the WM_THREAD message for threadbare Windows NSL_FORK

[vtailor]

One way to implement a thread in more recent versions of Windows
is to use SendMessage to initiate that thread.  You define a
WM_USER message called WM_THREAD, then subclass the main window
to include a WM_THREAD case.  The LPARAM of SendMessage then carries
a two-element structure containing the entry point of the thread
function and its parameter list.

Waiting for the thread to complete then involves testing for some
completion criterion while performing a PeekMessage loop.  This, of
course relies on the alleged pre-emptive multitasking of recent
Windows releases.