Synchronizing control flow in a tuplespace-based, distributed workflow management system

Abstract

Decentralized workflow enactment -- the process of evaluating control flow in a distributed manner -- is a key aspect of the implementation of a decentralized workflow management system (WfMS). A major challenge in this field is the support for join operations to synchronize concurrent threads of control flow. The original Linda model however does not provide operations for matching more than one tuple in a single operation -- complex logic needs to be implemented on the client side, having severe impact on performance and breaking the concept of coordination languages by mixing coordination and application logic. In this paper, we stress the need for an extended tuplespace model that natively supports the sync operation realizing WS-BPEL synchronizing joins directly on the tuplespace level. We pay special attention to the description of its semantics and propose an algorithm for efficient implementation on a single tuplespace. For the common case in distributed workflow enactment, where control flow is distributed over multiple tuplespaces, we present an optimization of the aforementioned algorithm in form of the sync pattern.