Verifying a simplification of mutual exclusion by Lycklama---Hadzilacos

A simplification of the mutual exclusion algorithm of Lycklama and Hadzilacos (ACM Trans Program Lang Syst 13:558---576, 1991 ) is presented. It uses only four nonatomic shared bits per thread to guarantee mutual exclusion with the first-come-first-served property. The algorithm is verified by assertional methods, aided by the proof assistant PVS. A variation with five bits per thread is also given. This variation may give better performance when the number of threads is large. The use of the proof assistant made it easy to transfer the proof of the main algorithm to the variation.