Abstract. Sequential consistency is the most widely used correctness condition for multiprocessor memory systems. This paper studies the problem of testing shared-memory multiprocessors to determine if they are indeed providing a sequentially consistent memory. It presents the first formal study of this problem, which has applications to testing new memory system designs and realizations, providing run-time fault tolerance, and detecting bugs in parallel programs.A series of results are presented for testing an execution of a shared memory under various scenarios, comparing sequential consistency with linearizability, another well-known correctness condition. Linearizability imposes additional restrictions on the shared memory, beyond that of sequential consistency; these restrictions are shown to be useful in testing such memories.

A general, modular technique for designing efficient leader finding algorithms in distributed, asynchronous networks is developed. This technique reduces the relatively complex problem of efficient leader finding to a simpler problem of efficient serial traversing of the corresponding network. The message complexity of the resulting leader finding algorithms is bounded by (where n is the number of nodes in the network [m is the number of edges in the network], k is the number of nodes that start the algorithm, and f (n) [ f (m)] is the message complexity of traversing the nodes [edges] of the network. This technique does not require that the FIFO discipline is obeyed by the links. The local memory needed for each node, besides the memory needed for the traversal algorithm, is logarithmic in the maximal identity of a node in the network. This result achieves in a unified way the best known upper bounds on the message complexity of leader finding algorithms for circular, complete and general networks. It is also shown to be applicable to other classes of networks, and in some cases the message complexity of the resulted algorithms is better by a constant factor than that of previously known algorithms.

Distributed algorithms for complete asynchronous networks of processors (i.e., networks where each pair of processors is connected by a communication line) are discussed. The main result is O(nlogn)lower and upper bounds on the number of messages required by any algorithm in a given class of distributed algorithms for such networks. This class includes algorithms for problems like finding a leader or constructing a sparming tree (as far as we know, all known algorithms for those problems may require

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