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A distributed system is an interconnected network of computing elements or nodes, each of which has its own storage. A distributed program is a collection of processes which execute asynchronously, possibly in different nodes of a distributed system, and they communicate with each other in order to realize a common goal. In such an environment, a group of processes may sometimes get involved in a communication deadlock. This is a situation in which each member process of the group is waiting for some member to communicate with it, but no member is attempting communication with it. In this paper, we present an algorithm for detecting such communication deadlocks. The algorithm is distributed, i.e., processes detect deadlocks during the course of their communication, without the aid of a central controller. The detection scheme does not presume any a priori structure among processes, and detection is made "on the fly" without freezing normal activities. The scheme does not require any storage whose size is determined by the size of the network, and hence is suitable also for an environment where processes are created dynamically. [ABSTRACT FROM AUTHOR]

A construct is proposed for parallel programming, called soma (software machine). A so,na is a sequential process that can communicate with other somas by exchanging messages via mailboxes. The soma construct is well suited for implementation on conventional as well as on distributed computer architectures, the main characteristic of the latter being the absence of a common store. In addition to a description of the soma construct, a rationale is given for its communication characteristics and a comparison is made with related proposals. Three illustrative examples are given: updating a sequential file (with concurrent operation of the input, update, and output activities), the general producer/consumer problem, and the computation of a critical path in a PERT graph. [ABSTRACT FROM AUTHOR]