Results about fast mutual exclusion

A fast mutual exclusion algorithm where only five accesses to the shared memory are needed in order to enter a critical section in the absence of contention is presented. In the presence of contention, the winning process may need to delay itself for 3×Δ time units, where Δ is an upper bound on the time taken by the slowest process to execute a statement involving an access to the shared memory. It is also proven that there is not two (or more) process mutual exclusion algorithm with an upper bound on the number of times a winning process needs to access the shared memory in order to enter its critical section in the presence of contention. However, under the assumption that busy-waiting counts as just one step, the authors present, for every fixed parameter k, an algorithm with the property that from a state where no process tries to enter its critical section, as long as the number of contenders does not exceed k, the time complexity of the winning process is a linear function of k. Finally, the ideas from the mutual exclusion algorithm are used to implement a fast and simple consensus algorithm