The predominant notion for specifying problems to study distributed computability are tasks. Notable examples of tasks are consensus, set agreement, renaming and commit-adopt. The theory of task solvability is well-developed using topology techniques and distributed simulations. However, concurrent computing problems are usually specified by objects. Tasks and objects differ in at least two ways. While a task is a one-shot problem, an object, such as a queue or a stack, typically can be invoked multiple times by each process. Also, a task, defined in terms of sets, specifies its responses when invoked by each set of processes concurrently, while an object, defined in terms of sequences, specifies the outputs the object may produce when it is accessed sequentially.
In a previous paper we showed how tasks can be used to specify one-shot objects (where each process can invoke only one operation, only once). In this paper we show how the notion of tasks can be extended to model any object. A potential benefit of this result is the use of topology, and other distributed computability techniques to study long-lived objects.
KeywordsDistributed problems Formal specifications Tasks Sequential specifications Linearizability Long-lived objects
Armando Castañeda was supported by UNAM-PAPIIT project IA102417. Sergio Rajsbaum was supported by UNAM-PAPIIT project IN109917. Part of this work was done while Sergio Rajsbaum was at École Polytechnique and Paris 7 University. Michel Raynal was supported the French ANR project DESCARTES (grant 16-CE40-0023-03) devoted to distributed software engineering. This work was also partly supported by the INRIA-UNAM Équipe Associée LiDiCo (at the Limits of Distributed Computing).
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