On 12/08/2012 05:58 PM, Eli Zaretskii wrote:

> buffer_shared is used only by xdisp.c, with the single exception of
> modify_overlay.  How about changing modify_overlay to compute this
> value by itself?

This is definitely possible (by enhancing window_loop, for example).
But now I'm thinking about maintaining per-buffer window counter,
which value is independent from the redisplay actions.  This opens
the way to a different optimizations (e.g. if we're modifying a buffer
which isn't shown in a window, we can avoid redisplay at all).

(My view of the whole thing is: Emacs global state is huge, and
redisplay is controlled by too much amount of global variables.
This is error-prone and makes some valuable things like threading
too complicated or even impossible. So it's desirable to deduce
redisplay actions from per-buffer/window/frame variables rather
than from the global ones.)

Dmitry