CDBottomUp.mesa
Copyright © 1985, 1986 by Xerox Corporation. All rights reserved.
Created by Christian Jacobi, December 13, 1985 5:49:59 pm PST
Last edited by: Christian Jacobi, October 15, 1986 2:12:44 pm PDT
CDBottomUp: CEDAR DEFINITIONS =
BEGIN
A module which allows easy implementation of bottom up calls which cache the results.
Each independent call creates a new invocation key. Results which are created with the same invocation key are allways trusted and taken from the cache. Results with a different invocation key are re-used if all the subcells haven't changed.
Calls for each application (class) - design pair should be monitored by the client, to prevent conflicts on the cached results and which invocation is the latest.
Class: TYPE = REF --READONLY-- ClassRec;
ClassRec:
TYPE =
RECORD [do:
PRIVATE DoProc, reUse:
PRIVATE ReUseProc, key:
PRIVATE
REF, classData:
REF];
--A class represents the application program; what analysis procedure should be called
Handle: TYPE = REF HandleRec;
HandleRec:
TYPE =
RECORD [class: Class, design:
CD.Design, data:
REF, invocation:
REF, r: Rope.
ROPE←
NIL, cnt:
INT𡤀];
--A handle represents one bottom up call sequence
--data, r, cnt are reserved for clients (there are never many HandleRec's arround)
DoProc:
TYPE =
PROC [handle: Handle, ob:
CD.Object]
RETURNS [val:
REF←
NIL];
--A DoProc should not recurse directly but may call DoRecurse to get recursion going
--If ~ob.class.inDirectory then results must NOT depend on design
--val: value which will be cached
ReUseProc:
TYPE =
PROC [handle: Handle, ob:
CD.Object, previousVal:
REF]
RETURNS [shouldDoAain:
BOOL�LSE];
--A ReUseProc should be fast and should not recurse directly nor call DoRecurse
Peek:
PROC [key:
REF, ob:
CD.Object]
RETURNS [val:
REF];
--Returns cached result; independent whether valid or not...
--key: as in Class registration
DoRecurse:
PROC [handle: Handle, ob:
CD.Object]
RETURNS [val:
REF, new:
BOOL];
--Gets value from cache or start recursion if value is not valid
--May be called recursively at clients own will; caches results (not slower then Peek)
--val: the result which was computed or cached
--new: whether a new result was computed this invocation (important for the engine room!)
--The automatic recursion calls only objects in the directory; however, if the client himself
-- calls DoRecurse for objects not in the directory, the procedures are invoked and the
-- results cached.
MakeHandle:
PROC [class: Class, design:
CD.Design←
NIL, data:
REF←
NIL, invocation:
REF←
NIL]
RETURNS [handle: Handle];
--Creates the handle data structure which will be passed through the recursion.
--class: determines application (procedures to be called)
--design: for client's use
--data: reserved for the client (implementor of class)
--invocation: invocation-key; (NIL for a new invocation-key)
StartRecurse:
PROC [class: Class, design:
CD.Design, ob:
CD.Object, data:
REF←
NIL]
RETURNS [val:
REF, new:
BOOL, handle: Handle];
--Short cut for DoRecurse[MakeHandle[...], ...]
Register:
PROC [do: DoProc, reUse: ReUseProc←
NIL, key:
REF←
NIL, reRegistrationKey:
REF←
NIL, classData:
REF←
NIL]
RETURNS [class: Class];
--Registers an application of CDBottomUp
--do: to be called bottom up for all objects in the directory. Do will typically
-- call DoRecurse to get recursion going; but for objects in the
-- directory, recursive calls of DoRecurse might have been precalled and
-- the result cached.
--reUse: is called to figure out whether objects which are already handled should
-- be handled again. It is called only for objects in the directory and
-- if do is not called anyway.
--key: property used to cache previous results; a NIL value creates a new property key.
-- The key property will be registered.
-- Clients must not access properties directly, but may use Peek.
-- Clients may remove cache by putting NIL on the key property.
--reRegistrationKey: property re-registration key; a NIL value ensures a new registration.
--class: identity of application.
END.