Parnas' Solution to the Readers/Writers

m1, m2, m3, r, w  : semaphore := 1
nreaders, nwriters : integer := 0

Reader Process {
  P(m3);
    P(r);
      P(m1);
      nreaders++;
      if (nreaders == 1) then P(w) fi;
      V(m1)
    V(r);
  V(m3);
  ... reading ...;
  P(m1);
  nreaders--;
  if (nreaders == 0) then V(w) fi;
  V(m1);
}

Writer Process {
  P(m2);
  nwriters++;
  if (nwriters == 1) then P(r) fi;
  V(m2);
  P(w);
  ... writing ...;
  V(w);
  P(m2);
  nwriters--;
  if (nwriters == 0) then V(r) fi;
  V(m2)
}