Lock Using Peterson’s Algorithm

Abstract

Chapter 2 defined a simple lock service for user threads 0, …, N − 1 and a program that implements the service. That implementation assumed only read-write atomicity and weak fairness, but it had an “arbiter” thread that continuously scanned for user requests. This chapter presents a program that implements the simple lock service for two threads without resorting to an arbiter thread. The program uses Peterson’s algorithm, the simplest known solution to the classical mutual exclusion problem for two threads. (The classical mutual exclusion problem is as follows. Given a program that has “critical sections” and is executed concurrently by N threads, to obtain “entry” and “exit” procedures to surround each critical section such that (1) at most one thread is inside a critical section at any time, and (2) any thread that starts the entry procedure eventually enters its critical section provided no thread stays indefinitely inside a critical section.)