In the group mutual exclusion problem, each critical section has a type or a group associated with it. Processes requesting critical sections of the same type may execute their critical sections concurrently. However, processes requesting critical sections of different types must execute their critical sections in a mutually exclusive manner. Most algorithms for group mutual exclusion that have been proposed so far implicitly assume that all groups are equally likely to be requested. In this paper, we propose an efficient algorithm for solving the problem when a relatively small number of groups are requested more frequently than others. Our algorithm has a message complexity of 2n − 1 per request for critical section, where n is the number of processes in the system. It has low synchronization delay of t and low waiting time of 2t, where t denotes the maximum message delay. The maximum concurrency of our algorithm is n, which implies that if all processes have requested critical sections of the same type, then all of them may execute their critical sections concurrently. Finally, the amortized message overhead of our algorithm is O(1). Our experimental results indicate that our algorithm outperforms the existing algorithms by as much as 50 % in some cases. KEY WORDS message-passing system, resource management, group mutual exclusion, token-based algorithm, non-uniform group access 1

The group mutual exclusion problem is an extension of the traditional mutual exclusion problem in which every critical section is associated with a type or a group. Processes requesting critical sections of the same type can execute their critical sections concurrently. However, processes requesting critical sections of different types must execute their critical sections in a mutually exclusive manner. We present an efficient distributed algorithm for solving the group mutual exclusion problem when processes are arranged in the form of a tree. Our algorithm is derived from Beauquier et al.’s group mutual exclusion algorithm for a tree network. The message complexity of our algorithm is at most 3hmax, wherehmax is the maximum height of the tree when rooted at any process. Its waiting time and synchronization delay, measured in terms of number of message hops, are at most 2hmax and hmax, respectively. Our algorithm has optimal synchronization delay for the class of tree network based algorithms for group mutual exclusion in which messages are only exchanged over the edges in the tree. Our simulation experiments indicate that our algorithm outperforms Beauquier et al.’s group mutual exclusion algorithm by as much as 70 % in some cases. Key words: distributed system, resource management, group mutual exclusion, tree network, optimal synchronization delay 1

Abstract—The group mutual exclusion (GME) problem is an interesting generalization of the mutual exclusion problem. Several solutions of the GME problem have been proposed for message passing distributed systems. However, none of these solutions is suitable for real time distributed systems. In this paper, we propose a token-based distributed algorithms for the GME problem in soft real time distributed systems. The algorithm uses the concepts of priority queue, dynamic request set and the process state. The algorithm uses first come first serve approach in selecting the next session type between the same priority levels and satisfies the concurrent occupancy property. The algorithm allows all n processors to be inside their CS provided they request for the same session. The performance analysis and correctness proof of the algorithm has also been included in the paper. Keywords—Concurrency, Group mutual exclusion, Priority, Request set, Token.

The group mutual exclusion (GME) problem is a generalization of the mutual exclusion problem. In group mutual exclusion, a process requests a session before entering its critical section (CS). Processes requesting the same session are allowed to be in their CS simultaneously, however, processes requesting different sessions must execute their CS in mutually exclusive way. The paper presents a token-based distributed algorithm for the GME problem in asynchronous message passing systems. The algorithm uses the concept of dynamic request sets. The algorithm does not use any message to be exchanged in the best case and uses n+1 messages in the worst case, where n is the number of processes in the system. The maximum concurrency of the algorithm is n and synchronization delay under heavy load (worst case) is 2T, where T is the maximum message propagation delay. The algorithm uses first come first serve approach in selecting the next session type and satisfies the concurrent occupancy property. The static performance analysis and correctness proof is also included in the present exposition.

Abstract—The group mutual exclusion (GME) problem is a variant of the mutual exclusion problem. In the present paper a token-based group mutual exclusion algorithm, capable of handling transient faults, is proposed. The algorithm uses the concept of dynamic request sets. A time out mechanism is used to detect the token loss; also, a distributed scheme is used to regenerate the token. The worst case message complexity of the algorithm is n+1. The maximum concurrency and forum switch complexity of the algorithm are n and min (n, m) respectively, where n is the number of processes and m is the number of groups. The algorithm also satisfies another desirable property called smooth admission. The scheme can also be adapted to handle the extended group mutual exclusion problem. Keywords—Dynamic request sets, Fault tolerance, Smooth admission, Transient faults.

The group mutual exclusion problem is an extension of the traditional mutual exclusion problem in which every critical section is associated with a type or a group. Processes requesting critical sections of the same type can execute their critical sections concurrently. However, processes requesting critical sections of different types must execute their critical sections in a mutually exclusive manner. We present an efficient distributed algorithm for solving the group mutual exclusion problem when processes are arranged in the form of a tree. Our algorithm is derived from Beauquier et al.’s group mutual exclusion algorithm for a tree network. The message complexity of our algorithm is at most 3hmax, where hmax is the maximum height of the tree when rooted at any process. Its waiting time and synchronization delay, measured in terms of number of message hops, are at most 2hmax and hmax, respectively. Our algorithm has optimal synchronization delay for the class of tree network based algorithms for group mutual exclusion in which messages are only exchanged over the edges in the tree. Our simulation experiments indicate that our algorithm outperforms Beauquier et al.’s group mutual exclusion algorithm by as much as 70 % in some cases.

Abstract—The group mutual exclusion problem extends the traditional mutual exclusion problem by associating a type (or a group) with each critical section. In this problem, processes requesting critical sections of the same type can execute their critical sections concurrently. However, processes requesting critical sections of different types must execute their critical sections in a mutually exclusive manner. We present a distributed algorithm for solving the group mutual exclusion problem based on the notion of surrogatequorum. Intuitively, our algorithm uses the quorum that has been successfully locked by a request as a surrogate to service other compatible requests for the same type of critical section. Unlike the existing quorum-based algorithms for group mutual exclusion, our algorithm achieves a low message complexity of OðqÞ and a low (amortized) bit-message complexity of OðbqrÞ, where q is the maximum size of a quorum, b is the maximum number of processes from which a node can receive critical section requests, and r is the maximum size of a request while maintaining both synchronization delay and waiting time at two message hops. As opposed to some existing quorum-based algorithms, our algorithm can adapt without performance penalties to dynamic changes in the set of groups. Our simulation results indicate that our algorithm outperforms the existing quorum-based algorithms for group mutual exclusion by as much as 45 percent in some cases. We also discuss how our algorithm can be extended to satisfy certain desirable properties such as concurrent entry and unnecessary blocking freedom. Index Terms—Message-passing system, resource management, mutual exclusion, group mutual exclusion, quorum-based algorithm. Ç