Abstract
Distributed systems, such as the Internet of Things (IoT) and cloud computing, are becoming popular. This requires modeling that reflects the natural characteristics of such systems: the locality of independent components, the autonomy of their decisions, and asynchronous communication. Automated verification of deadlocks and distributed termination supports rapid development. Existing techniques do not reflect some features of distribution. Most formalisms are synchronous and/or use some kind of global state, both of which are unrealistic. No model supports the communication duality that allows the integration of a remote procedure call and client-server paradigm into a single, uniform model. The majority of model checkers refer to total deadlocks. Usually, they do not distinguish between communication deadlocks from resource deadlocks and deadlocks from distributed termination. Some verification mechanisms check partial deadlocks at the expense of restricting the structure of the system being verified. The paper presents an original formalism for the modeling and verification of distributed systems. The Integrated Model of Distributed Systems (IMDS) defines a distributed system as two sets: states and messages, and the relationship of the “actions” between these sets. Communication duality provides projections on servers and on traveling agents, but the uniform specification of the verified system is preserved. General temporal formulas over IMDS, independent of the structure of the verified system, allow automated verification. These formulas distinguish between deadlocks and distributed termination, and between communication deadlocks and resource deadlocks. Partial deadlocks and partial termination can be checked. The Dedan tool was developed using IMDS formalism.
Highlights
Overview of the FormalismThe author’s experience with building industrial- and research-distributed systems showed that proper modeling and verification of such systems is crucial for their quality [1]
In the Institute of Computer Science, Warsaw University of Technology, a verification methodology based of original synchronous CSM formalism (Concurrent State Machines [2]) was developed and implemented in COSMA design tool [3,4]
Modern systems add a new dimension of difficulty to parallelism: independent nodes cooperating in a distributed environment
Summary
The author’s experience with building industrial- and research-distributed systems showed that proper modeling and verification of such systems is crucial for their quality [1]. The proposed IMDS formalism (Integrated Model of Distributed Systems [10,11]), combined with model checking using general temporal formulas, supports all the listed requirements It is based on a simple observation that the server in a distributed system, being in a given state, accepts the message and executes the action. The contributions of this paper are twofold: first, IMDS specification formalism supporting communication duality, locality, autonomy, and asynchrony of modeling; second, an automated verification technique for checking communication deadlocks, resource deadlocks, and distributed termination (both partial and total). The combination of these two techniques allowed for the development of the Dedan specification and verification environment.
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