Self-stabilizing mutual exclusion on a ring, even if K=N

We show that, contrary to common belief, Dijkstra's self-stabilizing mutual exclusion algorithm on a ring [Dij74,Dij82] also stabilizes when the number of states per node is one less than the number of nodes on the ring.Comment: 2 page

Automated Synthesis of Distributed Self-Stabilizing Protocols

In this paper, we introduce an SMT-based method that automatically synthesizes a distributed self-stabilizing protocol from a given high-level specification and network topology. Unlike existing approaches, where synthesis algorithms require the explicit description of the set of legitimate states, our technique only needs the temporal behavior of the protocol. We extend our approach to synthesize ideal-stabilizing protocols, where every state is legitimate. We also extend our technique to synthesize monotonic-stabilizing protocols, where during recovery, each process can execute an most once one action. Our proposed methods are fully implemented and we report successful synthesis of well-known protocols such as Dijkstra's token ring, a self-stabilizing version of Raymond's mutual exclusion algorithm, ideal-stabilizing leader election and local mutual exclusion, as well as monotonic-stabilizing maximal independent set and distributed Grundy coloring

Self-stabilizing K-out-of-L exclusion on tree network

In this paper, we address the problem of K-out-of-L exclusion, a generalization of the mutual exclusion problem, in which there are $\ell$ units of a shared resource, and any process can request up to $\mathtt k$ units ($1\leq\mathtt k\leq\ell$). We propose the first deterministic self-stabilizing distributed K-out-of-L exclusion protocol in message-passing systems for asynchronous oriented tree networks which assumes bounded local memory for each process.Comment: 15 page

Self-stabilizing tree algorithms

Designers of distributed algorithms have to contend with the problem of making the algorithms tolerant to several forms of coordination loss, primarily faulty initialization. The processes in a distributed system do not share a global memory and can only get a partial view of the global state. Transient failures in one part of the system may go unnoticed in other parts and thus cause the system to go into an illegal state. If the system were self-stabilizing, however, it is guaranteed that it will return to a legal state after a finite number of state transitions. This thesis presents and proves self-stabilizing algorithms for calculating tree metrics and for achieving mutual exclusion on a tree structured distributed system

Leader Election in Anonymous Rings: Franklin Goes Probabilistic

We present a probabilistic leader election algorithm for anonymous, bidirectional, asynchronous rings. It is based on an algorithm from Franklin, augmented with random identity selection, hop counters to detect identity clashes, and round numbers modulo 2. As a result, the algorithm is finite-state, so that various model checking techniques can be employed to verify its correctness, that is, eventually a unique leader is elected with probability one. We also sketch a formal correctness proof of the algorithm for rings with arbitrary size

Self-Stabilizing Wavelets and r-Hops Coordination

We introduce a simple tool called the wavelet (or, r-wavelet) scheme. Wavelets deals with coordination among processes which are at most r hops away of each other. We present a selfstabilizing solution for this scheme. Our solution requires no underlying structure and works in arbritrary anonymous networks, i.e., no process identifier is required. Moreover, our solution works under any (even unfair) daemon. Next, we use the wavelet scheme to design self-stabilizing layer clocks. We show that they provide an efficient device in the design of local coordination problems at distance r, i.e., r-barrier synchronization and r-local resource allocation (LRA) such as r-local mutual exclusion (LME), r-group mutual exclusion (GME), and r-Reader/Writers. Some solutions to the r-LRA problem (e.g., r-LME) also provide transformers to transform algorithms written assuming any r-central daemon into algorithms working with any distributed daemon

Verification of distributed algorithms with the Why3 tool

Dissertação de mestrado integrado em Informatics EngineeringNowadays, there currently exist many working program verification tools however, the developed tools are mostly limited to the verification of sequential code, or else of multi-threaded shared-memory programs. Due to the importance that distributed systems and protocols play in many systems, they have been targeted by the program verification community since the beginning of this area. In this sense, they recently tried to create tools capable of deductive verification in the distributed setting (deductive verification techniques offer the highest degree of assurance) and claim to have achieved impressive results. Thus, this dissertation will explore the use of the Why3 deductive verification tool for the verification of dis tributed algorithms. It will comprise the definition of a dedicated Why3library, together with a representative set of case studies. The goal is to provide evidence that Why3 is a privileged tool for such a task, standing at a sweet spot regarding expressive power and practicality.Nos dias de hoje, possuímos diversas ferramentas de verificação, ferramentas essas limitadas à verificação de código sequencial, ou então de programas multi-thread de memória partilhada. Devido à importância que os sistemas e protocolos distribuídos desempenham em muitos sistemas, estes foram alvos por parte da comunidade de verificação de programas desde o início desta área. Neste sentido, recentemente tentaram criar ferramentas capazes de realizar a verificação dedutiva no ambiente distribuído (técnicas de verificação dedutiva que oferecem o mais elevado grau de segurança) e afirmam ter alcançado resultados impressionantes. Assim, esta dissertação irá explorar o uso da ferramenta de verificação dedutiva Why3 com o propósito de verificar algoritmos distribuídos. Irão ser desenvolvidos modos e modelos da biblioteca Why3do, juntamente com um conjunto representativo de casos de estudos. O objetivo é fornecer evidências de que Why3 é uma ferramenta privilegiada para esta tarefa, estando no ponto ideal na relação poder expressivo e praticabilidade.This work is financed by the ERDF – European Regional Development Fund through the North Portugal Regional Operational Programme - NORTE2020 Programme and by National Funds through the Portuguese funding agency, FCT - Fundação para a Ciência e a Tecnologia within project NORTE-01-0145-FEDER-028550- PTDC/EEI-COM/28550/2017

Self-stabilizing protocol for anonymous oriented bi-directional rings under unfair distributed schedulers with a leader

We propose a self-stabilizing protocol for anonymous oriented bi-directional rings of any size under unfair distributed schedulers with a leader. The protocol is a randomized self-stabilizing, meaning that starting from an arbitrary configuration it converges (with probability 1) in finite time to a legitimate configuration (i.e. global system state) without the need for explicit exception handler of backward recovery. A fault may throw the system into an illegitimate configuration, but the system will autonomously resume a legitimate configuration, by regarding the current illegitimate configuration as an initial configuration, if the fault is transient. A self-stabilizing system thus tolerates any kind and any finite number of transient faults. The protocol can be used to implement an unfair distributed mutual exclusion in any ring topology network; Keywords: self-stabilizing protocol, anonymous oriented bi-directional ring, unfair distributed schedulers. Ring topology network, non-uniform and anonymous network, self-stabilization, fault tolerance, legitimate configuration