IF any_task_is_suspended_on(S) THEN
      unsuspend_one_task_suspended_on(S)
    ELSE
      increment(S)
these operations must be INDIVISIBLE, that is, they can not be interrupted

b: buffer(1..N);
t: integer:=0;	-- the number of items in buffer b

process producer
  i:element;
repeat
  produce (i);
  p(free_space_in_buffer);
  p(mutual_exclusion);
  append i to buffer b;			-- modifies t, b
  v(mutual_exclusion);
  v(item_in_buffer);
forever

process consumer
  j:element;
repeat
  p(item_in_buffer);
  p(mutual_exclusion);
  remove item from buffer into j;	-- modifies t, b
  v(mutual_exclusion)
  v(free_space_in_buffer);
  consume(j);
forever

TASK buffer_handler IS
  ENTRY append(item:element);
  ENTRY remove(item:OUT element);
END;

TASK BODY buffer_handler IS
  n: CONSTANT integer := 20;
  contents: ARRAY (1..n) OF element;
  cur_in, cur_out: integer RANGE 1..n:=1;
  tot: integer RANGE 0..n:=0;
BEGIN
  LOOP
    SELECT
      WHEN tot<n =>
      ACCEPT append(item: IN element) DO
        contents(cur_in) := item;
        cur_in := (cur_in MOD n) + 1;
        tot := tot + 1;
      END;
    OR
      WHEN tot > 0 =>
      ACCEPT remove(item: OUT integer) DO
        item := contents(cur_out);
        cur_out := (cur_out MOD N) + 1;
        tot := tot - 1;
      END;
    END SELECT;
  END LOOP;
END buffer_handler;