Federico Fariña

A distributed deadlock resolution algorithm for the AND model

Previous proposals for Distributed Deadlock Detection/Resolution algorithms for the AND model have the main disadvantage of resolving false deadlocks, that is, nonexisting or currently being resolved deadlocks. This paper provides an algorithm free of false deadlock resolutions, A simple specification for a safe deadlock resolution algorithm is introduced, and the new distributed solution is developed in a hierarchical fashion from its abstract specification. The algorithm is probe-based, uses node priorities, and coordinates the actions of resolvers so that false deadlocks are not resolved. The solution is formally proven correct by using the input-output Automata Model. Finally, a study about the liveness of the algorithm is provided.

Deformed fuzzy automata for correcting imperfect strings of fuzzy symbols

Presents a fuzzy method for the recognition of strings of fuzzy symbols containing substitution, deletion, and insertion errors. As a preliminary step, we propose a fuzzy automaton to calculate a similarity value between strings. The adequate selection of fuzzy operations for computing the transitions of the fuzzy automaton allows us to obtain different string similarity definitions (including the Levenshtein distance). A deformed fuzzy automaton based on this fuzzy automaton is then introduced in order to handle strings of fuzzy symbols. The deformed fuzzy automaton enables the classification of such strings having an undetermined number of insertion, deletion and substitution errors. The selection of the parameters determining the deformed fuzzy automaton behavior would allow to implement recognizers adapted to different problems. The paper also presents algorithms that implement the deformed fuzzy automaton. Experimental results show good performance in correcting these kinds of errors.

Efficient leader election in complete networks

Leader election is a fundamental problem in distributed computing and it has been studied assuming various computation models and network topologies. This paper analyzes the algorithms for leader election in complete networks using asynchronous communication channels. We present a novel algorithm that reduces the information necessary to select a leader compared with other leader election algorithms for complete networks. In this paper, the algorithm works without sense of direction. And, it does not require to know the number of nodes in the system. Our proposal requires O(n) messages and O(n) time, where n is the number of nodes in the system, to elect a leader.

An O(n) distributed deadlock resolution algorithm

This paper shows a new distributed algorithm for deadlock detection and resolution under the single-resource request model that highly improves the complexity measurements of previous proposals. The algorithm has a communication cost of 2n - 1 messages and a latency of n /spl middot/ T for a deadlock cycle of n processes, where T is the inter-site communication delay. The algorithm achieves this improvement even verifying the strongest correctness criteria considered in previous works: it resolves all deadlocks in finite time and does not resolve false deadlocks.

A safe algorithm for resolving OR deadlocks

Deadlocks in the OR model are usually resolved by aborting a deadlocked process. Prior algorithms for the same model sometimes abort nodes needlessly wasting computing resources. This paper presents a new deadlock resolution algorithm for the OR model that satisfies the following correctness criteria: (Safety) the algorithm does not resolve false deadlocks; (Liveness) the algorithm resolves all deadlocks in finite time. The communication cost of the algorithm is similar to that of previous nonsafe proposals. The theoretical cost has been validated by simulation. In addition, different algorithm initiation alternatives have been analyzed in order to reduce the latency of deadlocks.

AModified O(n) Leader Election Algorithm for Complete Networks

This paper presents a modified leader election algorithm for complete networks without sense of direction. The original algorithm, introduced by Villadangos et al. in (2005), had the aim of reducing the number of exchanged messages in order to select a leader. However, the original O(n) algorithm fails to choose a leader on several occasions. A modified algorithm, which eliminates the problems that cause the wrong behaviour, is proposed. It is formally proved that the new algorithm verifies the correctness criteria that consist of selecting a unique leader in every case. Additionally, the algorithm maintains the O(n) complexity in both messages and time, where n is the number of nodes in the system

A low communication cost algorithm for distributed deadlock detection and resolution

This work introduces a new distributed history-based algorithm for deadlock detection and resolution under the single-unit request model. The algorithm has a communication cost of O(n /spl middot/ log n) messages for a deadlock cycle of n processes. This low cost is achieved by means of two mechanisms. On one hand, to reduce the number of instance initializations, a node compares the priorities between its immediate successor and all its predecessors, starting the algorithm only if an antagonistic conflict is given. On the other hand, each instance of the algorithm runs at a certain detection level and does not retransmit probes created by instances running at a lower detection level. An instance can switch to a higher level depending on the information received in the probes.

Mobility management in cellular communication systems using fuzzy systems

Mobility management in cellular communication systems is needed to guarantee quality of service, and to offer advanced services based on the user location. High mobility of terminals determines a high effort to predict next movement in order to grant a correct transition to the next phone cell. Then a fuzzy method dealing with the problem of determining the propagation path of a mobile terminal is introduced in this paper. Since multi-path fading and attenuation make difficult to determine the position of a terminal, the use of fuzzy symbols to model this situation allows to work better with this imprecise (fuzzy) information. Finally, the use of a fuzzy automaton allows to improve significatively the final recognition rate of the path followed by a mobile terminal.

A Dynamic Deadlock Detection/Resolution Algorithm with Linear Message Complexity

Leader election and deadlock detection/resolution are different problems in distributed computing. However, the problem of selecting a candidate to resolve a detected deadlock is quite similar to the problem of selecting a leader in a virtual ring. In this paper we exploit this similarity and the fact that leader election is a well-known problem with optimal solutions. We have adapted an O(n) leader election algorithm for complete networks, in order to implement a deadlock resolution algorithm with the same cost. The adaptation consists in adding dynamic features to the leader election algorithm, ensuring that it works properly even when the wait-for relations in the system change at the same time as the algorithm runs. The algorithm guarantees that only just up-to-date information remains in the system, thus reducing the communication cost unlike previous linear proposals.

Approximate String Matching Using Deformed Fuzzy Automata: A Learning Experience

Deformed fuzzy automata are complex structures that can be used for solving approximate string matching problems when input strings are composed by fuzzy symbols. Different string similarity definitions are obtained by the appropriate selection of fuzzy operators and parameters involved in the calculus of the automaton transitions. In this paper, we apply a genetic algorithm to adjust the automaton parameters for selecting the ones best fit to a particular application. This genetic approach overcomes the difficulty of using common optimizing techniques like gradient descent, due to the presence of non-derivable functions in the calculus of the automaton transitions. Experimental results, obtained in a text recognition experience, validate the proposed methodology.