>    Date: Sat, 13 Jul 1996 23:29:08 -0600
>    From: Warner Losh <imp@village.org>
> 
>    Sun, when they were writing Solaris, is rumored to have produced
>    "warlock."  This program would go through all your sources and warn
>    of potential deadlock situations in them.  They never released it
>    as they considered it a competitive advantage to them...
> 
> Solaris kernel also has a debugging feature, it's called "deadman".
> Every so often a timer based callout runs which runs down all the
> mutex/semaphore/spinlock holder lists in the kernel and panics if any
> circular and/or deadlock cases are found.

The IBM database design manual indicates several methods of fast
computation of transitive closure over acyclic directed  graphs
which make this kind of kludge unnecessary.  IMO, deadlock
avoidance beats deadlock detection any day of the week.  Consider
the issue of a two context deadly embrace for a resource: how do
you unwind state so you don't lose already processed context?  In
the deadlock detection case, the anser is "you probably don't".  Or
you go to some overly complicated cruft, like the system call
interrupt code in the trap, using a longjmp to unwind the stack.


					Regards,
					Terry Lambert
					terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.