Atomic semantics

Atomic semantics is a type of guarantee provided by a data register shared by several processors in a parallel machine or in a network of computers working together.

A read/write register R stores a value and is accessed by two basic operations: read and write(v).

A read returns the value stored in R and write(v) changes the value stored in R to v. A register is called atomic if it satisfies the two following properties: 1) Each invocation op of a read or write operation: •Must appear as if it were executed at a single point τ(op) in time.

Atomic/Linearizable register: Termination: when a node is correct, sooner or later each read and write operation will complete.

An atomic register could be defined for a variable with a single writer but multi- readers (SWMR), single-writer/single-reader (SWSR), or multi-writer/multi-reader (MWMR).