Accession Number : ADA264351
Title : On the Robustness of Herlihy's Hierarchy
Descriptive Note : Special technical rept.
Corporate Author : CORNELL UNIV ITHACA NY DEPT OF COMPUTER SCIENCE
Personal Author(s) : Jayanti, Prasad
Report Date : Mar 1993
Pagination or Media Count : 35
Abstract : A wait-free hierarchy maps object types to levels in Z(+)(Union) (infinity) and has the following property: if a type T is at level N, and T' is an arbitrary type, then there is a wait-free implementation of an object of type T', for N processes, using only registers and objects of type T. The infinite hierarchy defined by Herlihy is an example of a wait-free hierarchy. A wait-free hierarchy is robust if it has the following property: if T is at level N, and S is a finite set of types belonging to levels N - 1 or lower, then there is no wait-free implementation of an object of type T, for N processes, using any number and any combination of objects belonging to the types in S. Robustness implies that there are no clever ways of combining weak shared objects to obtain stronger ones. Contrary to what many researchers believe, we prove that Herlihy's hierarchy is not robust. We then define some natural variants of Herlihy's hierarchy, which are also infinite wait-free hierarchies. With the exception of one, which is still open, these are not robust either. We conclude with the open question of whether non-trivial robust wait-free hierarchies exist.
Descriptors : *COMPUTER COMMUNICATIONS , *HIERARCHIES , *ASYNCHRONOUS COMPUTERS , COMPUTER ARCHITECTURE , MULTIPROCESSORS , MAPS
Subject Categories : Operations Research
Distribution Statement : APPROVED FOR PUBLIC RELEASE