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Unclassified 2a. SECURITY CLASSIFICATION AUTHORITY 3. DISTRIBUTION /AVAILABILITY OF REPORT Approved for ,.ublic release; distribution 2b. DECLASSIFICATION/ DOWNGRADING SCHEDULE is unlimited. 4. PERFORMING ORGANIZATION REPORT NUMBER(S) S. MONITORING ORGANIZATION REPORT NUMBER(S) MIT/LCS/TM-429 N00014-83-K-0125 6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION MIT Lab for Computer Science (If applicable) Office of Naval Research/Dept. of Navy 6c. ADDRESS (City, State. and ZIPCode) 7b. ADDRESS(Oty, State, and ZIPCode)

No abstract

This paper is concerned with the solvability of the problem of processor renaming in unreliable, completely asynchronous distributed systems. Fischer et al. prove in [S] that "nontrivial consensus" cannot be attained in such systems, even when only a single, benign processor failure is possible. In contrast, this paper shows that problems of processor renaming can be solved even in the presence of up to t c n/2 faulty processors, contradicting the widely held belief that no nontrivial problem can be solved in such a system. The problems deal with renaming processors so as to reduce the size of the initial name space. When only uniqueness of the new names is required, we present a lower bound of n + 1 on the size of the new name space, and a renaming algorithm that establishes an upper bound on n + t. If the new names are required also to preserve the original order, a tight bound of 2'(n -t + 1) -1 is obtained.

An atomic snapshot memory is a shared data structure allowing concurrent processes to store information in a collection of shared registers, all of which may be read in a single atomic scan operation. This paper presents three wait-free implementations of atomic snapshot memory. Two constructions implement wait-free single-writer atomic snapshot memory from wait-free atomic single-writer, n-reader registers. A third construction implements a wait-free n-writer atomic snapshot memory from n-writer, n-reader registers. The first implementation uses unbounded