Ellogon and the challenge of threads

This paper is about the Ellogon language engineering platform, and the challenges faced in modernising it, in order to better exploit contemporary hardware. Ellogon is an open-source infrastructure, specialised in natural language processing. Following a data model that closely resembles TIPSTER, Ellogon can be used either as an autonomous application, offering a graphical user interface, or it can be embedded in a C/C++ application as a library. Ellogon has been implemented in C/C++ and Tcl/Tk: in fact Ellogon is a vanilla Tcl interpreter, with the Ellogon core loaded as a Tcl extension, and a set of Tcl/Tk scripts that implement the GUI. The core component of Ellogon, being a Tcl extension, heavily relies on Tcl objects to implement its data model, a decision made more than a decade ago, which poses difficulties into making Ellogon a multi-threaded application.