Copyright (C) 1994, Digital Equipment Corp.
by Steve Glassman, Mark Manasse and Greg Nelson
<*PRAGMA LL*>
GENERIC INTERFACE RingBuffer(Elem);
Elem.T must not be an open array type;
Elem.NormalSize must be a constant positive integer.
A RingBuffer.T represents an unmonitored indefinitely expandible
FIFO queue.
TYPE T =
RECORD
lo, hi: CARDINAL := 0;
buff: REF ARRAY OF Elem.T := NIL
END;
(* buff[lo..hi-1] circularly are the active entries;
lo = hi => the queue is empty; lo # hi => buff # NIL. *)
CONST Empty = T{0, 0, NIL};
<*INLINE*> PROCEDURE IsEmpty(READONLY rb: T): BOOLEAN;
Return whether rb is empty.
PROCEDURE Insert(VAR rb: T; READONLY e: Elem.T);
Insert e into rb, extending rb if necessary.
EXCEPTION Exhausted;
PROCEDURE Remove(VAR rb: T): Elem.T RAISES {Exhausted};
Raise the exception if rb is empty, else remove the
oldest element of rb and return it.
PROCEDURE Peek(VAR rb: T): Elem.T RAISES {Exhausted};
Like Remove, but leave the returned element at the head of the queue.
END RingBuffer.