IMPLEMENTATION OF THE CONVERSATION SCHEME IN MESSAGE-BASED DISTRIBUTED COMPUTER-SYSTEMS

This paper discusses several different approaches for implementing conversations in message-based distributed computer systems (DCS's). Important implementation factors to be considered include the control of exits of processes upon completion of their conversation tasks and the approach to execution of the conversation acceptance test. Two different exit control strategies, one in a synchronous manner and the other in an asynchronous manner, and three different approaches to execution of the conversation acceptance test, centralized, decentralized, and semi-centralized, are examined and compared in terms of system performance and implementation cost. A new efficient approach to run-time management of recovery information based on an extension of the recovery cache scheme is also discussed. The effectiveness of these execution approaches also depends on the way conversations are structured initially by program designers. Therefore, the two major types of conversation structures, Name-Linked Recovery Block (NLRB) and Abstract Data Type (ADT) Conversations, are examined to analyze which execution approaches are the most efficient for each conversation structure. These results provide useful guidelines for implementing conversations in message-based DCS's. As a case study, an unmanned vehicle system is used to illustrate how the identified approaches to implementation of the conversation scheme can be used in a realistic real-time application.