[DGD] 3 golden rules for MP

[Felix A. Croes]

1) Try to modify as few objects as possible in a single execution round,
   other than the object you start in.
2) Try to avoid modifying the object you add a callout for.  If possible,
   delay modification until when the callout actually executes.
3) Avoid starting all execution rounds from the same small set of objects.

About terminology: I decided to call the time slice during which an LPC
event program is running an "execution round".  It's not really a thread,
and talking about them as "threads" confuses the issue when you also have
to deal with actual threads.

Regards,
Dworkin