Concurrency

In the previous chapters, we described several models of computation that reflect different ways in which the process of computation can be understood. All these different abstract models of computation share one characteristic: The goal is to express sequential algorithms. To describe the meaning of a sequential program, we can use an operational approach in which we see an algorithm as a black box transforming some given input data into the desired output. However, in some contexts, for example when describing the behaviour of an operating system, this input-output abstraction is not well suited. The final result of the algorithm might not be of interest, or the notion of “final” might not even apply. Indeed, an operating system does stop running in some cases, typically when we shut down our computer, but then we are not expecting a “result” from the computation.