Path: utzoo!utgpu!water!watmath!clyde!att!ucbvax!ICAEN.UIOWA.EDU!dbfunk
From: dbfunk@ICAEN.UIOWA.EDU (David B. Funk)
Newsgroups: comp.sys.apollo
Subject: Re: Suspending processes (was questions for the gurus)
Message-ID: <8809151847.AA10608@umaxc.weeg.uiowa.edu>
Date: 15 Sep 88 18:46:05 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 38

There are 2 ways to really suspend a process, a suspend signal and a
(undocumented) suspend system call.

    If a process is given a fault_$suspend_proc signal it will stop
execution until it receives a fault_$continue_proc signal (look
in /sys/ins/fault.ins.{pas,c,ftn} for their definition). To give
one of these signals you will have to use /com/sigp with the "-c"
option. EG: '$ sigp -c 120027 process_151' will cause process_151
to stop execution. In a pst it will be listed as in a Wait state
but a 'tb process_151' will show that it is in a suspend fault
condition.
     WARNING, only a continue signal will take it out of the
suspend. If the process receives some other type of signal first,
such as a stop or quit, the other signal will block the continue
signal and the process is in gridlock and can only be blasted.
So if you have any questions as to what a waiting process is up
to, first do a 'tb' on it. If you see something like:

  $ tb siologin_1
  In System Service "ec2_$wait"
  Called from Diagnostic Frame - process suspend fault (OS/fault handler)
  Called from "GET_IT" line 931
  Called from "SIO_GET" line 964
  Called from "STREAM_$GET_REC" line 150
  Called from "readline" line 67
  Called from "builtin" line 651
  ...

then give that process a "-c 12002b" signal before doing any thing else
to it.
    The DM 'ds' and 'dc' commands use undocumented system calls to suspend
and continue a process. These work in the kernal and actually change the
process manager dispatch status. This will show up in a pst state as 'Susp'.
This is safer as a 'dc' cannot be blocked by another signal but the process
must be continued before it will respond to any signal. IE you will have to
continue it before your stop or kill signals will take effect.

   Dave Funk    dbfunk@icaen.uiowa.edu