Formal Analysis of the Bakery Protocol with Consideration of Nonatomic Reads and Writes

The bakery protocol is the first real solution of the mutual exclusion problem. It does not assume any lower mutual exclusion protocols. The bakery protocol has been often used as a benchmark to demonstrate that proposed verification methods and/or tools are powerful enough. But, the true bakery protocol has been rarely used. We have formally proved that the protocol satisfies the mutual exclusion property. The proof is mechanized with CafeOBJ, an algebraic specification language, in which state machines as well as data types can be specified. Nonatomic reads and writes to shared variables are formalized by representing an assignment to a shared variable with multiple atomic transitions. Our formal model of the protocol has states in which a shared variable is being modified. A read to the variable in such states obtains an arbitrary value, which is represented as a CafeOBJ term.