Beyond Atomic Registers: Bounded Wait-Free Implementations of Nontrivial Objects

We de ne 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 modi es 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 modi es. We consider a class of shared data objects that can either be read, written, or modi ed 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.