Redesigning Tcl-DP

Tcl-DP is a loadable module for Tcl that adds advanced communication features to Tcl/Tk. Tcl-DP supports communication by serial links, IP-multicast, TCP, UDP, and email, contains a remote procedure call (RPC) mechanism, and supports the design of new protocols using modules called filters. Tcl-DP 1.0 [Smi93] was released four years ago and has since been used for numerous commercial and academic projects. With age, however, the code became so brittle that adding new features and porting to new versions of Tcl was nearly impossible. Furthermore, many of Tcl-DP's original features were incorporated in the Tcl core, making them redundant in Tcl-DP. Hence, we decided to write the latest version of Tcl-DP (version 4.0) from scratch. In this paper, we describe the new features of Tcl-DP 4.0, its architecture and implementation, and problems we encountered with Tcl's new I/O system.