A Starvation-Free Solution to the Mutual Exclusion Problem

With three or more cyclic processes competing for the critical section, however, there is a danger of individual starvation when the Pand V-operations are so-called ‘weakly implemented’. When the semaphore operations are weakly implemented and a V(m) is executed, which process is allowed to proceed is left undefined when two or more processes are blocked by P(m). .As a result, there is a danger of individual starvation on account of ‘infinite overtaking’. To preclude this danger, it is not unusual to postulate for the P and V-operations a so-called ‘strong implementation’ in which infinite overtaking is impossible. CLe form of strong implementation is to admit the processes to the critical section in the order of first-come-first-served. A starvation-free solution to the mutual exclusion problem for an unknown number of processes and under the constrain! of employing only a fixed number of weak semaphores has been conjectured not to exist [ 2 1. This paper refutes the conjecture by presenting an algorithm that solves the problem. The solution makes use of three binary semaphores that are assumed to enjoy the following weak property.