A Model of Actors and Grey Failures

Abstract

Existing models for the analysis of concurrent processes tend to focus on fail-stop failures, where processes are either working or permanently stopped, and their state (working/stopped) is known. In fact, systems are often affected by grey failures: failures that are latent, possibly transient, and may affect the system in subtle ways that later lead to major issues (such as crashes, limited availability, overload). We introduce a model of actor-based systems with grey failures, based on two interlinked layers: an actor model, given as an asynchronous process calculus with discrete time, and a failure model that represents failure patterns to inject in the system. Our failure model captures not only fail-stop node and link failures, but also grey failures (e.g., partial, transient). We give a behavioural equivalence relation based on weak barbed bisimulation to compare systems on the basis of their ability to recover from failures, and on this basis we define some desirable properties of reliable systems. By doing so, we reduce the problem of checking reliability properties of systems to the problem of checking bisimulation.

A model of actors and grey failures

“…Extensions with respect to the conference paper. This work is an extended version of the conference paper appeared in COORDINATION 2022 [BLTV22] with the following additional contributions:…”

“…• The syntax and semantics of systems have been extended to model checkpoints. We have added Section 4.2 to show that the extension can still express the systems in [BLTV22] (Proposition 4.11). In a new section, Section 5.3, we show that the notion of n-recoverability…”

“…given in [BLTV22] is not suitable for systems with checkpoints. We have therefore added, in Section 5.3, a more relaxed notion of n-recoverability for checkpointing systems.…”

“…We have therefore added, in Section 5.3, a more relaxed notion of n-recoverability for checkpointing systems. • We found a flaw in the definition of n-recoverability given in [BLTV22]. We have fixed in this extended version.…”

“…We have fixed in this extended version. In Section 5.1 we give an amended definition of n-recoverability alongside the one given in [BLTV22], and discuss the differences by examples.…”