The Case of Unreliable Base Objects

Abstract

The previous chapter presented universal constructions that allow one to build implementations of any object defined by a sequential specification (on total operations) that are wait-free, i.e., that tolerate any number of process crashes. As we have seen, these constructions rest on two types of objects: atomic read/write registers and consensus objects. These universal constructions assume that these base objects are reliable; namely, they implicitly consider that their behavior always complies with their specification. As an example, given an atomic register \(R\), it is assumed that an invocation of \(R.\mathsf{{read}}()\) always returns the last value that was written into \(R\) (“last” is with respect to the linearization order). Similarly, given a consensus object \( CONS \), an invocation \( CONS .\mathsf{{propose}}()\) is assumed to always return the single value decided by this consensus object.