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From: BOTCHAIR@UOGUELPH.BITNET (Alex Bewley)
Newsgroups: comp.lang.modula2
Subject: Code for thought
Message-ID: <INFO-M2%87110722341208@UCF1VM>
Date: Sat, 7-Nov-87 22:14:37 EST
Article-I.D.: UCF1VM.INFO-M2%87110722341208
Posted: Sat Nov  7 22:14:37 1987
Date-Received: Tue, 10-Nov-87 05:11:23 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: Info-Modula2 Distribution List <INFO-M2%UCF1VM.bitnet@jade.berkeley.edu>
Organization: The ARPA Internet
Lines: 47


   This is just an idea off the top of my head, and haven't really considered
if it would be possible.  So, I'm going to ask all of you.

   As you all know, one can create processes in Modula-2.  Suppose you were to
design a system that was totally process oriented (ie. each procedure was
made into a process).  Could you make a time scheduler process (run with
IOTRANSFER off the system clock) to switch other processes (ie. force them
to switch) giving each one equal cpu time?  Here's some sample (may not work)
code.

...
ProcessList = ARRAY [0..10] OF PROCESS;
...

PROCEDURE TimeScheduler;
BEGIN
  IOTRANSFER(TimeSchedule,ProcessList[i],1Ch); (* pc timer interrupt *)
  IF clockticks = thisamount THEN
    INC(i):
    TRANSFER(ProcessList[i-1],ProcessList[i]);
  END;
END TimeScheduler;

PROCEDURE A; BEGIN SimpleTerm.WriteString("Hi there - A"); END A;

PROCEDURE B; BEGIN SimpleTerm.WriteString("Hi there - B"); END B;

PROCEDURE C; BEGIN SimpleTerm.WriteString("Hi there - C"); END C;

BEGIN
  ...
  NEWPROCESS(Ap,ADR(workspace),SIZE(workspace),A);
  ProcessList[0] := Ap;
  ...
  NEWPROCESS(TimeSchedule, ADR(workspace), SIZE(workspace), TimeScheduler);
  TRANSFER(mainP, TimeSchedule);
  ...
END;

  The code is far from grammitically correct, but hopefully you get the idea.

  Suppose task switching is not possible this way.  How would one go about
doing it in Modula-2.

      Alex Bewley
      BOTCHAIR@UOGUELPH