Coordinated Atomic Actions: from Concept to Implementation

The Coordinated Atomic Action (or CA action) concept is a unified scheme for coordinating complex concurrent activities and supporting error recovery between multiple interacting objects in a distributed object-oriented system. It provides a conceptual framework for dealing with different kinds of concurrency and achieving fault tolerance by extending and integrating two complementary concepts — conversations and transactions. Conversations (enhanced with concurrent exception handling) are used to control cooperative concurrency and to implement coordinated error recovery whilst transactions are used to maintain the consistency of shared resources in the presence of failures and competitive concurrency. This paper explains the CA action concept in detail and then addresses related design issues such as multi-thread coordination, exception handling and resolution, coordinated access to shared objects and provision of software fault tolerance. Finally, brief details are given of a number of experimental prototype implementations and case studies.