The Read/Write Register Abstraction

Abstract

The read/write register is the most basic object of sequential computing. This chapter introduces it in a concurrency context, and considers three associated consistency conditions: regularity, atomicity (also called linearizability), and sequential consistency. Atomicity and sequential consistency define the family of strong consistency conditions, namely, they require all processes to agree on the same total order in which they see the read and write operations applied to the registers. After a formalization of these notions, the chapter shows that atomic read/write registers compose for free while sequentially consistent registers do not.