From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,5b86cfa15b273e36
X-Google-Attributes: gid103376,public
From: tmoran@bix.com (Tom Moran)
Subject: Re: Protected types made of ADT's, and Passive Iterators
Date: 1998/09/05
Message-ID: <35f1a607.136859@SantaClara01.news.InterNex.Net>#1/1
X-Deja-AN: 388247133
References: <udpvdbl8uf.fsf@tanana.llnl.gov> <m3btou4urs.fsf@mheaney.ni.net>
Organization: InterNex Information Services 1-800-595-3333
Newsgroups: comp.lang.ada
Date: 1998-09-05T00:00:00+00:00
List-Id: <comp.lang.ada>

>procedure Modify_Items (Collection : in out Collection_Type) is
>...
>begin
>   Seize (Collection.Guard);
> do stuff
> Release(Collection.Guard);
>end Modify_Items;
  A way to lessen the chance of missing/excess Seize/Release is to
make a controlled type
  type Ptr_To_Collection_Type is access all Collection_Type;
  type Check_Busy_Type(P : Ptr_To_Collection_Type) is new
Ada.Finalization.Controlled with null record;.
  Inside any routine that needs to have serialized access to a
Collection_Type, put a declaration, eg
procedure Modify_Items (Collection : in out Collection_Type) is
  Grab : Check_Busy_Type(access Collection);
...
begin
  Then the Initialize of Check_Busy_Type will be certainly be called
and can do the Seize, and the Finalize can do the release.  It just
requires one line of code (the "Grab" declaration) added to existing
routines and does not depend on the programmer remembering to Seize
and Release at the right places.  (I simplify, but just slightly.)