Beyond atomic registers: bounded wait-free implementations of nontrivial objects

Abstract

We define a class of operations called pseudo read-modify-write (PRMW) operations, and show that nontrivial shared data objects with such operations can be implemented in a bounded wait-free manner from atomic registers. A PRMW operation is similar to a “true” read-modify-write (RMW) operation in that it modifies the value of a shared variable based upon the original value of that variable. However, unlike an RMW operation, a PRMW operation does not return the value of the variable that it modifies. We consider a class of shared data objects that can either be read, written, or modified by an associative, commutative PRMW operation, and show that any object in this class can be implemented without waiting from atomic registers. The implementations that we present are polynomial in both space and time and thus are an improvement over previously published ones, all of which have unbounded space complexity.