ui/src/picture/FreeList.mg

 Copyright (C) 1992, Digital Equipment Corporation 
 All rights reserved. 
 See the file COPYRIGHT for a full description. 
 Last modified on Wed Oct 13 17:36:52 PDT 1993 by sfreeman 


GENERIC MODULE FreeList(Elem);

 where Elem is an Image.T and so has a field



      next: Elem.T := NIL;


   and a method.



       destroy();



      New (): Elem.T;


   returns an Elem.T object, possibly from the free list.  Elem.Ts from
   this procedure will be put onto the free list and destroy() will be
   called.



      Free(t: Elem.T)


   explicitly calls t.destroy() and puts it on the free list 


IMPORT WeakRef, PictureRep;

VAR
  freeMu         := NEW(MUTEX);
  free  : Elem.T := NIL;

PROCEDURE New (): Elem.T =
  VAR res: Elem.T := NIL;
  BEGIN
    LOCK freeMu DO
      IF free # NIL THEN res := free; free := res.next; END;
    END;
    IF res = NIL THEN res := NEW(T); END;
    EVAL WeakRef.FromRef(res, CleanUp);
    RETURN res;
  END New;

PROCEDURE CleanUp (<*UNUSED*> READONLY w: WeakRef.T; r: REFANY) =
  BEGIN
    Free(NARROW(r, Elem.T));
  END CleanUp;

PROCEDURE Free (t: Elem.T) =
  BEGIN
    t.destroy();
    LOCK freeMu DO t.next := free; free := t; END;
  END Free;

BEGIN
END FreeList.