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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham
	autolearn_force=no version=3.4.4
X-Google-Thread: 103376,e0e1d3b3f7c994b8
X-Google-Attributes: gid103376,domainid0,public,usenet
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news4.google.com!news.germany.com!news.belwue.de!LF.net!news.enyo.de!not-for-mail
From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: Robert Dewar's great article about the Strengths of Ada over
 other langauges in multiprocessing!
Date: Fri, 28 Mar 2008 00:10:30 +0100
Message-ID: <87prtfzrtl.fsf@mid.deneb.enyo.de>
References: <13t4b2kkjem20f3@corp.supernews.com>
	<89af8399-94fb-42b3-909d-edf3c98d32e5@n75g2000hsh.googlegroups.com>
	<fr4916$vo7$1@jacob-sparre.dk> <87bq56peg1.fsf@mid.deneb.enyo.de>
	<wvbrprthzjbf.fsf@astra06.norway.sun.com>
	<87bq516uri.fsf@mid.deneb.enyo.de>
	<wvbrlk44zf5l.fsf@astra06.norway.sun.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
X-Trace: idssi.enyo.de 1206659430 2928 212.9.189.177 (27 Mar 2008 23:10:30
 GMT)
X-Complaints-To: 
Cancel-Lock: sha1:gboEcviHggblWI5oF8xizuwEqvc=
Xref: g2news1.google.com comp.lang.ada:20608
Date: 2008-03-28T00:10:30+01:00
List-Id: <comp.lang.ada>

* Ole-Hjalmar Kristensen:

> If you mean that it may be difficult to optimize, I agree, but I
> cannot agree that you need *more* than an entryless protected object
> to implement a hash table, since it guarantees that each operation on
> the object is indivisible. 

You need some kind of signaling construct.  Suppose you put some access
value as a value into the hash table.  If there's no signaling (the case
of an entryless protected object, it seems), a task that retrieves the
value from the table cannot make any assumptions regarding the object
the access value refers to, unless there is some other form of
synchronization.

> On the other hand, I cannot see any reason why Annex C just couldn't
> say that intrinsic subprograms for compare-amd-swap and similar
> machine operations shall be provided *if* they are available on a
> platform.

CAS alone is not sufficient, you also need some sort of barrier (both
against compiler optimizations and reordering in the silicon).