Extended process registry for erlang

Abstract

The built-in process registry has proven to be an extremely useful feature of the Erlang language. It makes it easy to provide named services, which can be reached without knowing the process identifier of the serving process. However, the current registry also has limitations: names can only be atoms (unstructured), processes can register under at most one name, and it offers no means of efficient search and iteration. In Ericsson's IMS Gateway products, a recurring task was to maintain mapping tables in order to locate call handling processes based on different properties. A common pattern, a form of index table, was identified, and resulted in the development of an extended process registry. It was not immediately obvious that this would be worthwhile, or even efficient enough to be useful. But as implementation progressed, designers found more and more uses for the extended process registry, which resulted in significant reduction of code volume and a more homogeneous implementation. It also provided a powerful means of debugging systems with many tens of thousand processes. This paper describes the extended process registry, critiques it, and proposes a new implementation that offers more symmetry, better performance and support for a global namespace.