Implicit locking in the Ensemble concurrent object-oriented graphics editor

Abstract

Ensemble is an X-Windows based, object-oriented graphics editor based on the tgif graphics editor from UCLA. It relies on Unix 4.3bsd sockets and can be used as a stand-alone program or as an application in the University of Florida's distributed conferencing system (DCS). It uses implicitly placed write locks for concurrency control, with locks placed when an object is selected and removed when it is deselected. Multiple users may read or edit a file concurrently, with all users receiving updates whenever a lock is removed. Pointers are shared by mutual consent, so that users may collaborate to the degree desired. Ensemble is a prototype lock-based approach to object-oriented concurrent graphics editing.