The problem of the mutual exclusion of several
independent processes from simultaneous access to a
"critical section" is discussed for the case where there
are two distinct classes of processes known as "readers"
and "writers." The "readers" may share the section
with each other, but the "writers" must have exclusive
access. Two solutions are presented: one for the case
where we wish minimum delay for the readers; the other
for the case where we wish writing to take place as early
as possible.