Private storage, static storage, bound modules and service programs

Okay, I've completely confused myself now.

I have values that I like to keep for an entire job, and values I like
to keep at a program level.  So, Program A calls Program B, and they
share a job level value J_SESSION, but each has its own program level
value, P_CALLLEVEL.

Typically, I have a separately bound program I call that keeps the job
level values, and I bind in a module to keep static variables at the
program level.  So, I have a program that returns J_SESSION, and both
Program A and Program B call it through an EXTPGM call.  However, each
has its own P_CALLLEVEL value, which it gets through an EXTPROC call to
a bound module.

In the world of service programs, can I emulate this?  Barring getting
into activation groups, it seems to me that the only way I can keep data
at the program level is by a module bound to that program.  It seems to
me that all calls to a service program from the same job regardless of
the opposition of the calling program in the call stack will always have
the same global variables.

As I look at this, it SEEMS as though activation groups might allow me
to do something.  If I put each program in the stack in its own
activation group and had one service program with a named activation
group and the other with an activation group of *CALLER, it seems that
the first service program's global storage would be shared among the
programs, while the second service program's variable would be unique
for each program.

That's a pretty elegant concept, although it does mean I have to have an
activation group for every level of my stack.  But in the great scheme
of things, that doesn't seem to be all bad.

Comments?

Joe