Summary: Fast and Scalable Mutual Exclusion ?
James H.Anderson and YongJik Kim
Department of Computer Science
University of North Carolina at Chapel Hill
Abstract. We present an Nprocess algorithm for mutual exclusion un
der read/write atomicity that has O(1) time complexity in the absence
of contention and \Theta(log N) time complexity under contention, where
``time'' is measured by counting remote memory references. This is the
first such algorithm to achieve these time complexity bounds. Our algo
rithm is obtained by combining a new ``fastpath'' mechanism with an
arbitrationtree algorithm presented previously by Yang and Anderson.
Recent work on mutual exclusion  has focused on the design of ``scalable'' algo
rithms that minimize the impact of the processortomemory bottleneck through
the use of local spinning . A mutual exclusion algorithm is scalable if its perfor
mance degrades only slightly as the number of contending processes increases.
In localspin mutual exclusion algorithms, good scalability is achieved by requir
ing all busywaiting loops to be readonly loops in which only locallyaccessible
shared variables are accessed that do not require a traversal of the processor
tomemory interconnect. A shared variable is locally accessible on a distributed