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/**************************************************************************/
PERE ET FILS
( Father & Sons )
An example of creating REENTRANT processes
by Jean-Michel Forgeas
June 1987
/**************************************************************************/
IMPORTANT:
----------
This files are placed into Public Domain by the author.
You can freely distribute them for non-commercial purposes
on condition that they all stay together:
proc.h include file (message structure)
Pere.c 'father' source
Fils.c 'child' source
StartProc.asm startup source
Pere executable
Fils executable
StartProc.obj object file to link with
pere-et-fils.doc this file
/* ----------------------------------------------------------------------- */
To try it out:
--------------
Set your current directory to pere-et-fils drawer.
Then type Pere Fils [n] ( n - the number of processes you want,
try 4 first time).
To stop them all:
-----------------
Write 'logoff' into every window.
'Pere' stops itself after the last 'fils'.
HOW IT WORKS:
-------------
Father loads ones the child code into memory and then starts as many
processes as you want over it. The code is as a pure body,
the process is the spirit to bring this body to life.
Father opens 2 MsgPorts. The first one is used for children
initilisation and to recieve their answers ( Ok or error codes).
Then, father changes the ReplyPort in the message structure
to his second port so to dialog with child process through father's
second port.
Father process then can start another child using the first
MsgPort.
Every child detects the initialisation message coming to his port
and creates an additional port so not to use the one in the
Process structure. Before answering 'Ok' to the father, he places
the address of his new port in the message so that father will know
to where send his messages.
As every child has its own message, every message contains the
address of the MsgPort of his child.
Children behave as a terminals and the code that make them work
is in the father.
So you can create as many child processes as you wish all using
the same code that exists only ONES in memory.
Of course, each child's DATA should be different.
Use AllocMem to reserve space for child's static variables. You can
use automatic variables since they are placed onto stack but
static and global variables should be used with great care since
all chilren will read and write to them all at the same time.
StartProc.obj:
--------------
It is modified astartup.obj to allow for reentrant code. It is
possible not to use startup at all and kill processes with RemTask(),
but it's better to use startup for 2 reasons:
- cause exit() function is very handy;
- RemTask doesn't return the memory (AllocMem) and other
resources used by the task it is going to remove;
STATIC & GLOBAL variables:
--------------------------
The easy way to use static and global variables in your reentrant
code is to define one structure that contains all your variables
and then call AllocMem with image of this structure. Then you
would pass an address of this structure through all of your
function calls.
COMPILE INSTRUCTIONS:
---------------------
This example MUST be compiled with Lattice C (3.10 or 3.03).
LC1 -iINCLUDE: Pere
LC2 -v Pere
BLink FROM LIB:AStartup.obj+Pere.o TO Pere
LIBRARY LIB:Amiga.lib+LC.lib VERBOSE NODEBUG
LC1 -iINCLUDE: Fils
LC2 -v Fils
BLink FROM LIB:StartProc.obj+Fils.o TO Fils
LIBRARY LIB:Amiga.lib VERBOSE NODEBUG
CONTACT:
--------
J-M. Forgeas,
21 rue Voltaire,
92300 Levallois Perret,
FRANCE