Atomic data abstractions in a distributed collaborative editing system

Abstract

This paper describes our experience implementing CES, a distributed Collaborative Editing System written in Argus, a language that includes facilities for managing long-!ived distributed data. Argus provides atomic actions, which simplify the handling of concurrency and faihres, and mechanisms for implementing atomic data ~5'pes, which ensure serializability and recoverability of actions that use them. This paper focuses on the support for atomicity in Argus, espedatly the support for building new atomic types. Overall the mechanisms in Argus made it relatively easy to build CES; however, we encountered interesting problems in several areas° For example, much of the processing of an atomic action in Argus is handled automatically by the run4ime system; several examples are presented that illustrate areas where more explicit control in the implementations of atomic types would be useful.

Groupware: some issues and experiences

“…The editor transparently manages locking and synchronization, and users edit the shared object as they would a private object. Examples include the Collaborative Editing System (CES) [28], Shared Book [58], and Quilt [22,57]. Some multiuser editors provide explicit notification of other users' actions.…”

“…Tickle locks [28] allow the lock to be released to another requester after an idle period; soft locks [17] allow locks to be broken by explicit override commands. Numerous other schemes notify users when locks are obtained or conflicting requests submitted.…”

“…Transaction mechanisms have allowed for successful concurrency control in non-real-time groupware systems, such as CES [28] and Quilt [22,57]. For real-time groupware, these mechanisms present several problems.…”

Locking without requesting a lock: A consistency maintenance mechanism in Internet-based real-time group editors

“…Therefore, the lock should be released such that not only the former lock owner but also other users can edit it. This functionality is similar to Greif, Seliger and Weihl's "tickle lock" that reassigns the lock if the current holder is inactive [7]. Similarly, the "pause detection" mechanism automatically releases a lock after a prescribed period (in terms of the physical clock) of inactivity [5].…”

Fault Tolerant Software Technology for Distributed Computer Systems

“…These primitive atomic data types also define the synchronization properties of the user-constructed types. Experience with programming a distributed, collaborative editing system in Argus has been described by Greif et al [Grei86a]; one criticism arising out of this experience was that they were sometimes forced to use a Guardian where a cluster might have been more appropriate.…”