Re: Patch to trunk: merge common code in hourglass impl

[Jason Rumney <jasonr@gnu.org>]

Eli Zaretskii wrote:
> Yes, atimers work by sending SIGALRM, which isn't supported on
> Windows.  While Windows has equivalent functionality, no one stepped
> forward to emulate atimers, probably because their use in Emacs is
> quite limited, and in areas where Windows offers alternate ways of
> doing the same.
>   

What is the equivalent functionality? Threads are not the same as 
signals, as they do not block other threads from executing. This is a 
problem when any Lisp code is run, as a GC can occur in the main Lisp 
thread while the signal emulation thread is running Lisp code, leading 
to memory corruption and crashes. So any system timers need to be 
handled in the Lisp thread, which effectively means they are 
synchronous. Since the hourglass code doesn't actually need to run Lisp, 
I used a Windows system timer running in the UI thread, which is not 
generally busy enough to have delays like the Lisp thread, but I don't 
think a general atimer implementation can be done that way.