identity of the caller?

[Bob Horvath]

Is there any way to find out the identity of who called you?  I am
mainly thinking of method calls, but in general if there is a way
for regular function calls, I would be interested in that too.

I suppose I should give some context.   We have a tool that draws
message flow diagrams for communications systems.  These flows are
similar to use case flows, or ITU Z.120 MSC charts if you know
what those are.  The tools takes simple ascii text which has the
sender, the receiver, and the message name, as in...

SENDER RECEIVER MessageName

We tend to have to enumerate a lot of these, and I had the thought
that if I could prototype the functionality of the nodes, they
could generate the text used to generate the drawings.

What I was thinking is that the receivers of the message would
define methods that handle them.  To get the picture right,
I would need to print out method name, the receiver, and who sent
it.  It is the "who sent it" bit that I can't visualize a solution
for.