Results about fast mutual exclusion

We present 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. In the presence of contention, the winning process may need to delay itself for 3 • A time units, where A is an upper bound on the time taken by the slowest process to execute a statement involving an access to the shared memory. We also prove that there is no 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 presence of contention. However, under the assumption that busy-waiting counts as just one step, we 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, we use the ideas from the mutual exclusion algorithm to implement a fast and simple consensus algorithm.