ui/src/split/SelectQueue.i3

 Copyright (C) 1992, Digital Equipment Corporation                         
 All rights reserved.                                                      
 See the file COPYRIGHT for a full description.                            
                                                                           
 by Steve Glassman, Mark Manasse and Greg Nelson           
 Last modified on Mon Feb 24 13:54:25 PST 1992 by muller   
      modified on Wed Sep 11 15:33:44 PDT 1991 by msm      

<*PRAGMA LL*>

INTERFACE SelectQueue;

IMPORT VBT;

TYPE Elem = RECORD v: VBT.T; cd: VBT.MiscRec END;

TYPE T =
  RECORD
    lo, hi: CARDINAL := 0;
    buff: REF ARRAY OF Elem := 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);

 Insert e into rb, extending rb if necessary. 

EXCEPTION Exhausted;

PROCEDURE Remove(VAR rb: T): Elem RAISES {Exhausted};

 Raise the exception if br is empty, else remove the
   oldest element of rb and return it. 

END SelectQueue.