Path: news.daimi.aau.dk!news.uni-c.dk!nntp-oslo.UNINETT.no!nntp-trd.UNINETT.no!nntp.uib.no!torget.bgnett.no!aage.priv.no!Norway.EU.net!EU.net!main.Germany.EU.net!fu-berlin.de!zrz.TU-Berlin.DE!news
From: Kai Petzke <wpp@marie.physik.tu-berlin.de>
Newsgroups: comp.lang.beta
Subject: Re: [Q] Unique names
Date: Fri, 06 Sep 1996 23:10:57 +0200
Organization: Technical University Berlin, Germany
Lines: 47
Message-ID: <32309361.6E8349A4@marie.physik.tu-berlin.de>
References: <yyeg24xkvzl.fsf@viola.daimi.aau.dk>
NNTP-Posting-Host: dial1-89.zrz.tu-berlin.de
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Mailer: Mozilla 2.02 (X11; I; Linux 2.0.0 i586)

Chris Ranzau Hansen wrote:
> 
> Hello,
> 
> I'm building a prototype of a persistent store. I need some way to
> create unique names for the objects to be saved. At the moment I'm
> using the pattern time. The problem is that the result only changes
> once every second. I'm thinking of adding a counter so that I can
> create more than one unique name per sec.

When you have a persistent store, why not put a single object there,
that represents a counter, that yields a different serial number each
time, it is accessed, eg:

	counter:
	  (# state: @integer
	     get: IntegerValue (# do state+1->state->value #);
	     init: (# do 0->state #);
	  #);

When you first create the persistent store, you do something like:

	ps: ^persistentstore;
	count: ^counter;
     do
	&persistentstore[]->ps[];
	'store'->ps.create;
	&counter[]->count[];
	count.init;
	(count[], 'counter')->ps.put;

When you later access the persistent store, use:

	ps: ^persistentstore;
	count: ^counter;
     do
	&persistentstore[]->ps[];
	'store'->ps.openWrite;
	('counter',counter##)->ps.get->count[];


The `checkpoint' and `close' routine of the persistentstore will
automatically ensure, that the updated counter value is written back
into the persistentstore, if required.
-- 
Kai
wpp@marie.physik.tu-berlin.de