Hierarchical token based mutual exclusion algorithms

Mutual exclusion is a basic block of distributed synchronization algorithms. One of the challenge in highly distributed environments (like peer-to-peer or Grid configurations) is to provide scalable synchronizations taking into account the hierarchical network topology. This paper proposes hierarchical mutual exclusion algorithms. These algorithms are extensions of the Naimi-Trehel's token algorithm, reducing the cost of latency and the number of messages exchanges between far hosts. We propose three main extensions : (1) hierarchical proxy-based approach, (2) aggregation of requests, and (3) token preemption by closer hosts. We compared the performance of these algorithms on an emulated Grid testbed. We study the impact of each of the extensions, showing that the combination of them can greatly improve performances of the original algorithm

Global synchronization algorithms for the Intel iPSC/860

In a distributed memory multicomputer that has no global clock, global processor synchronization can only be achieved through software. Global synchronization algorithms are used in tridiagonal systems solvers, CFD codes, sequence comparison algorithms, and sorting algorithms. They are also useful for event simulation, debugging, and for solving mutual exclusion problems. For the Intel iPSC/860 in particular, global synchronization can be used to ensure the most effective use of the communication network for operations such as the shift, where each processor in a one-dimensional array or ring concurrently sends a message to its right (or left) neighbor. Three global synchronization algorithms are considered for the iPSC/860: the gysnc() primitive provided by Intel, the PICL primitive sync0(), and a new recursive doubling synchronization (RDS) algorithm. The performance of these algorithms is compared to the performance predicted by communication models of both the long and forced message protocols. Measurements of the cost of shift operations preceded by global synchronization show that the RDS algorithm always synchronizes the nodes more precisely and costs only slightly more than the other two algorithms

Constant RMR Solutions to Reader Writer Synchronization

We study Reader-Writer Exclusion, a well-known variant of the Mutual Exclusion problem where processes are divided into two classes--readers and writers--and multiple readers can be in the Critical Section (CS) at the same time, although no process may be in the CS at the same time as a writer. Since readers don\u27t conflict with each other, they should not obstruct each other. Specifically, the concurrent entering property must be satisfied: if all writers are in the remainder section, each reader should be able to enter the CS in a bounded number of its own steps. Three versions of the Reader-Writer Exclusion problem are commonly studied--one where writers have priority over readers, another where readers have priority, and the last where neither class has priority over the other and no process may starve. To ensure high performance on Cache-Coherent (CC) and Distributed Shared Memory (DSM) multiprocessors, algorithms should be designed to generate as few remote memory references (RMRs) as possible. The ideal would be to achieve constant RMR complexity, i.e., the worst case number of RMRs that a process generates in order to enter and exit the CS once is a constant, independent of the number of processes. Constant RMR complexity algorithms have existed for Mutual Exclusion for two decades, but none exists for Reader-Writer Exclusion. Danek and Hadzilacos\u27 lower bound proof implies that it is impossible to achieve sublinear RMR complexity for DSM machines. For CC machines, the best existing bound, also due to Danek and Hadzilacos , is O(log n), where n is the number of processes. In this work, we present the first constant RMR complexity algorithms for all three versions of the Reader-Writer Exclusion problem (for CC machines)

Algon: a framework for supporting comparison of distributed algorithm performance

Programmers often need to use distributed algorithms to add non-functional behaviour such as mutual exclusion, deadlock detection and termination, to a distributed application. They find the selection and implementation of these algorithms daunting. Consequently, they have no idea which algorithm will be best for their particular application. To address this difficulty the Algon framework provides a set of pre-coded distributed algorithms for programmers to choose from, and provides a special performance display tool to support choice between algorithms. The performance tool is discussed. The developer of a distributed application will be able to observe the performance of each of the available algorithms according to a set of of widely accepted and easily-understandable performance metrics and compare and contrast the behaviour of the algorithms to support an informed choice. The strength of the Algon framework is that it does not require a working knowledge of algorithmic theory or functionality in order for the developer to use the algorithms

An asynchronous message-passing distributed algorithm for the global critical section problem

This paper considers the global $(l,k)$-CS problem which is the problem of controlling the system in such a way that, at least $l$ and at most $k$ processes must be in the CS at a time in the network. In this paper, a distributed solution is proposed in the asynchronous message-passing model. Our solution is a versatile composition method of algorithms for $l$-mutual inclusion and $k$-mutual exclusion. Its message complexity is $O(|Q|)$, where $|Q|$ is the maximum size for the quorum of a coterie used by the algorithm, which is typically $|Q| = \sqrt{n}$.Comment: This is a modified version of the conference paper in PDAA201