E.B.:
> > One thread monitors multiple file handles (event sources), and
> > processes events one at a time. Examples of events are client
> > requests and DNS replies. This is how postscreen is implemented.
>
> OK, so concurrent in that you could start accepting a new
> SMTP session while an earlier one is waiting on a DNS lookup?
The basic idea is that network roundtrips take longer than simple
local operations, thanks to the speed of light.
Of course this works up to a limit, and that limit is high enough
that it does not matter for Postfix. Sites that need to handle a
lots of concurrent requests will be using multiple MTAs long before
postscreen would saturate.
Wietse
