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1

Causal-Consistent Replay Reversible Semantics for Message Passing Concurrent Programs

Lanese Ivan, Palacios Adrián, Vidal Germán

Fundamenta Informaticae

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2021

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Vol. 178, nr 3

229--266

EN

Causal-consistent reversible debugging is an innovative technique for debugging concurrent systems. It allows one to go back in the execution focusing on the actions that most likely caused a visible misbehavior. When such an action is selected, the debugger undoes it, including all and only its consequences. This operation is called a causal-consistent rollback. In this way, the user can avoid being distracted by the actions of other, unrelated processes. In this work, we introduce its dual notion: causal-consistent replay. We allow the user to record an execution of a running program and, in contrast to traditional replay debuggers, to reproduce a visible misbehavior inside the debugger including all and only its causes. Furthermore, we present a unified framework that combines both causal-consistent replay and causal-consistent rollback. Although most of the ideas that we present are rather general, we focus on a popular functional and concurrent programming language based on message passing: Erlang.

2

Reversible Limited Automata

Kutrib M., Wendlandt M.

Fundamenta Informaticae

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2017

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Vol. 155, nr 1/2

31--58

EN

A k-limited automaton is a linear bounded automaton that may rewrite each tape square only in the first k visits, where k≥ 0 is a fixed constant. It is known that these automata accept context-free languages only. We investigate deterministic k-limited automata towards their ability to perform reversible computations, that is, computations in which every configuration has at most one predecessor. A first result is that, for all k≥ 0, sweeping k-limited automata accept regular languages only. In contrast to reversible finite automata, all regular languages are accepted by sweeping 0-limited automata. Then we study the computational power gained in the number k of possible rewrite operations. It is shown that the reversible 2-limited automata accept regular languages only and, thus, are strictly weaker than general 2-limited automata. Furthermore, a proper inclusion between reversible 3-limited and 4-limited automata languages is obtained. The next levels of the hierarchy are separated between every k and k + 3 rewrite operations. We investigate closure properties of the family of languages accepted by reversible k-limited automata. It turns out that these families are not closed under intersection, but are closed under complementation. They are closed under intersection with regular languages, which leads to the non-closure under concatenation, iteration, and homomorphisms. Finally, it turns out that all k-limited automata accept Church-Rosser languages only, that is, the intersection between context-free and Church-Rosser languages contains an infinite hierarchy of language families beyond the deterministic context-free languages.

3

Universal Reversible Turing Machines with a Small Number of Tape Symbols

Morita K.

Fundamenta Informaticae

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2015

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Vol. 138, nr 1/2

17--29

EN

We study the problem of finding small universal reversible Turing machines (URTMs) with four symbols or less. Here, we present two models of URTMs: a 24-state 4-symbol URTM, and a 32-state 3-symbol URTM. Both of them are designed so that they can simulate cyclic tag systems, a kind of string rewriting systems that are universal. By converting the 24-state 4-symbol URTM into a 2-symbol machine, we also obtain a 138-state 2-symbol URTM.

4

Two-Way Reversible Multi-Head Finite Automata

Morita K.

Fundamenta Informaticae

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2011

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Vol. 110, nr 1-4

241-254

EN

A two-way reversible multi-head finite automaton (RMFA) is introduced as a simple model of reversible computing, and its language accepting capability is studied. We show that various non-regular context-free languages, and non-context-free context-sensitive languages are accepted by RMFAs with a few heads. For example, we give an RMFA with three heads that accepts the language consisting of all words whose length is a prime number. A construction method of a garbage-less RMFA from a given RFMA is also shown.