Path: utzoo!mnetor!uunet!husc6!necntc!dandelion!ulowell!apollo!rees
From: rees@apollo.uucp (Jim Rees)
Newsgroups: comp.sys.apollo
Subject: Re: Suspending processes
Message-ID: <393d7157.b8ab@apollo.uucp>
Date: 23 Dec 87 16:58:00 GMT
References: <179@idacom.UUCP>
Organization: Apollo Computer, Chelmsford, Mass.
Lines: 14
Keywords: DC DS suspend

You can use proc_$suspend and resume, which is what the DM uses, but
they are less than ideal.  They do an unconditional suspend at the
proc2 level, which is below all the user space locking.  So if you
manage to suspend some process while it is holding some critical
lock, say the sfcb lock, you're in for trouble.  If you've ever had
the DM say "unable to lock needed resources," this is what's going
on.

A much better way, that uses released interfaces, is to use the
unix SIGSTOP (unfortunate name, not related to fault_$stop) and
SIGCONT signals.  These interact correctly with user space locks.
The proc2 versions should only be necessary if you have some process
that's totally wedged in an inhibited loop, and if you do, you're
going to have to blast it anyway.