Critical Section Entry Research Articles

A Hybrid Algorithm to Solve Group Mutual Exclusion Problem in Message passing Distributed Systems

In the present paper, we propose a hierarchical algorithm to solve the group mutual exclusion (GME) problem in clusterbased systems. We consider a two-level hierarchy in which the nodes are divided in to clusters and a node in each cluster is designated as coordinator which is essentially the cluster head. The number of global messages per critical section entry in our algorithm depends upon the number of clusters in the system unlike most of the existing GME algorithms where it depends upon the total number of nodes in the system. Performance of the algorithm directly depends on the coherent behavior of nodes inside clusters. The results have been substantiated with extensive simulation. A fault tolerant extension of the algorithm has also been proposed in the present exposition.

An algorithm for k-mutual exclusion in decentralized systems

The distributed k-mutual exclusion problem or, simply the k-mutex problem, is the problem of allowing at most k processes to access their critical sections simultaneously. This might be the consequence where k identical copies of a resource are made available in the distributed system or that the resource by its nature can be accessed by at most k processes simultaneously. When a process enters it critical section such that there are l < k processes in their critical sections, there is no interference of the mutual exclusion condition. In this paper, we present an algorithm for the k-mutex problem. The algorithm is token based and k tokens are used. A node may enter the critical section only if it possesses a token. The algorithm has a worst case message complexity of O ( n ) . Under heavy load the message requirement approaches 2 per critical section entry. The algorithm has been modified to enable fault tolerant capabilities. We have discussed node failure, message loss and link failure.

UN NUEVO ALGORITMO DISTRIBUIDO DE EXCLUSIÓN MUTUA QUE MINIMIZA EL INTERCAMBIO DE MENSAJES

In this paper we present a new token-based distributed mutual exclusion algorithm. The algorithm relies on two distributed dynamic structures in order to provide mutual exclusion: the “Naimi Forest” to route token requests, and the “Raymond Virtual Tree” to serve token requests. Our strategy combines the best characteristics of two algorithms cited as the most efficient in the literature concerning message traffic. We present a performance simulation study. Results show that our algorithm has better performance considering the number of message exchanged per critical section entry.

Empirical Evaluation of Mutual Exclusion Algorithms for Distributed Systems

Mutual exclusion in distributed memory systems is realized by passing messages among sites to establish a sequence for the waiting sites to enter the critical section. We have evaluated various distributed mutual exclusion algorithms on the IBM SP2 machine and the Intel iPSC/860 system, with their empirical results compared in terms of such criteria as the number of message exchanges and response time. The results take into account the effects of critical section request rate, critical section duration, and system size. Our results indicate that the Star algorithm (1991, M. L. Neilsen and M. Mizuno, in “Proc. 11th Int. Conf. Distributed Computing Systems,” pp. 354–360) achieves the shortest response time in most cases among all the algorithms on a small to medium-sized system, when sites request the critical section many times before involving any barrier synchronization. This is because (1) it requires the exchange of no more than three messages per critical section entry, and (2) contention can quickly be alleviated after several entries into the critical section, if no barrier synchronization is involved in the meantime. On the other hand, if every site enters the critical section only once before encountering a barrier, the improved Ring algorithm (1995, S. S. Fu and N.-F. Tzeng, “Efficient Token-Based Approach to Mutual Exclusion in Distributed Memory Systems,” Tech. Rep. TR-95-8-1, CACS, Univ. Southwestern Louisiana, Lafayette) is found to outperform others under a heavy load; but the Star algorithm and the CSL algorithm (1990, Y. I. Chang, M. Singhal, and M. T. Liu, in “Proc. 1990 Int. Conf. Parallel Processing,” Vol. III, pp. 295–302) prevail when the request rate becomes light. The best solution to mutual exclusion in distributed memory systems is determined by how participating sites generate their mutual exclusion requests.

A Comparison of Fast and Low Overhead Distributed Priority Locks

Distributed synchronization is necessary to coordinate the diverse activities of a distributed system. Priority synchronization is needed for real-time systems or to improve the performance of critical tasks. Practical synchronization techniques require fast response and low overhead. In this paper, we present three priority synchronization algorithms that sendO(logn) messages per critical section request on average and useO(logn) bits of storage per processor. Previous algorithms required 2(n− 1) messages per critical section entry andO(n) bits of storage per processor. Two of the algorithms are based on Li and Hudak's path compression techniques, and the third algorithm uses Raymond's fixed-tree structure. Since each of the algorithms have the same theoretical complexity, we make a performance comparison to determine which of the algorithms is best under different loads and different request priority distributions. We find that when the request priority distribution is stationary, the path-compression algorithm that uses a singly linked list is best overall, but the fixed-tree algorithm requires fewer messages when the number of processors is small and the load is high (100% or greater). When the request priority distribution is nonstationary, the fixed-tree algorithm requires the fewest messages when the load is 100% or greater.

On mutual exclusion in faulty distributed systems

In this paper, we present an extension of the fault-tolerant mutual exclusion algorithm of [1] to make it deadlock-free when a node requesting critical section or when a node executing its critical section fails. The proposed algorithm requires O (&amp;radic; tn ) messages per critical section entry (in a network of n nodes) and O ( t &amp;radic; tn ) messages when a node fails ( t &amp;minus; 1 is the upper bound of the node failures).

A logical-time-based approach to decentralised resource allocation in distributed systems

The Time Frame Resource Request (TFRR) scheme is presented as a method for achieving temporal agreement in distributed systems. The scheme is based on prior agreement between sender and receiver processes on the exchange of a data message. The implications of this agreement for the advancement of virtual time are examined in detail. A global synchronisation based on TFRR can be used to solve the distributed mutual exclusion problem. In a group of n potential contenders, the solution necessitates the sending of at most n + 1 messages per contending process and n − 1 messages per non-contending process for each critical section entry.

Achieving mutual exclusion in a distributed computing environment

A distributed control algorithm, called MEAL, is presented for achieving mutual exclusion in a distributed computing environment. It requires only ( N + 2) messages per critical section entry, in the no failures case; N being the number of nodes in the distributed system. Few assertions are proved to verify the correct functioning of MEAL. Possible modification to make it resilient, in case of node failures, are also suggested.