Xtrace: a highlevel extension of Tcl-trace
Florian Murr (Siemens AG, CT IC 7)
Manfred Burger (Siemens AG, CT IC 7)
Tcl has much of the famous "observer pattern" built into the language through
the Tcl-"trace" command.
While the Tcl-trace command is best suited for building new commands
or control contructs, the observer pattern is often used in a distributed
This paper describes the "Xtrace" package which provides functionality
that builds upon "trace add variable" and extends it, to be more high-level
and support the needs of a distributed observer pattern.
In a basic distributed setting, there is a "model" composed of XOTcl
objects that resides at the server. Multiple clients are observers-of /
actors-on this model, residing in different processes or even on different
machines. The clients are able to change the model, through setting of
variables, or through method calls and these changes get propagated back
to the clients, assuring that all clients mirror the current state of the
Xtrace does interprocess communication over sockets using a companion
XOTcl package "xcom" that will also be introduced.