RE: More ILE 101

[Joel Cochran <jrc@xxxxxxxxxx>]

On Mon, 2004-04-12 at 22:02, Joe Pluta wrote:
> Reading your article, it seems that while those variables are not shared
> between jobs, they are shared between programs in different activation
> groups in the same if you use ACTGRP(named) on your service program.

Actually, to be specific, they are not shared at all.  What is shared is
the access to the activation group.  Instead of having fifty copys of
the service programs and hence its global variables, then there is just
one copy that gets accessed from fifty different places.  The appearance
is that the global variable is shared, but in reality it is the
activation group that is shared.

> They are not share if you use *CALLER, provided the two calling programs
> are in different activation groups.

Correct, because each CALLER gets its own copy of the service program
and its variable, the access of which it cannot share with any other
activation group.

> Oh boy... this gets interesting quickly.

You bet!  Since you know Java, think of the global variable in a service
program running a named activation group as Public Static variable in a
Java class, just without the object reference.

This is why I said you really need to understand at development time
what effect the activation group choice has on the rest of the
application.  I think the most commonly expected behavior occurs when
you use *CALLER for service programs.  The call to the service program
"belongs" to the activation group of the caller and so is somewhat
self-contained.  It gets interesting when you use a named activation
group intentionally to retain variable states across the entire job
regardless of the calling activation group.

I demonstrated this technique in another article earlier this month:

http://www.midrangeserver.com/fhg/fhg040704-story01.html

By using a named activation group for the security system, I can avoid
repeated calls to the database by pre-loading a service program with the
values and then simply accessing them anywhere I go in my application.

And sorry to everyone for bombarding the list like this, but I'm reading
through all these at once...

Joel
http://www.rpgnext.com