Summary: due to the fact that each twoprocess entry and exit sec
tion of Peterson's algorithm requires fewer remote op
erations outside of busywaiting loops than does ours.
This gives rise to the following open question: how many
remote operations outside of busywaiting loops are re
quired in twoprocess read/write algorithms based on
We end the paper with a few observations concerning
the time complexity of concurrent algorithms. A natu
ral approach to measuring the time complexity of such
an algorithm would be to simply count the number of
operations. However, a straightforward application of
such an approach does not provide any insight into the
behavior of mutual exclusion algorithms under heavy
contention. In particular, in any algorithm in which pro
cesses busywait, the number of operations needed for
one process to get to its critical section is unbounded.
In order to serve as a measure of time complexity, a
measure should be both intuitive and easy to compute.
In sequential programming, the usual measure of time