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=unavailable autolearn_force=no version=3.4.4
Path: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Safety of unprotected concurrent operations on constant objects
Date: Sat, 03 May 2014 22:40:31 +0100
Organization: A noiseless patient Spider
Message-ID: <lya9aybkxc.fsf@pushface.org>
References: <slrnlm6mkg.i0l.lithiumcat@nat.rebma.instinctive.eu>
	<7403d130-8b42-43cd-a0f1-53ba34b46141@googlegroups.com>
	<slrnlmals8.i0l.lithiumcat@nat.rebma.instinctive.eu>
Mime-Version: 1.0
Content-Type: text/plain
Injection-Info: mx05.eternal-september.org;
 posting-host="6c8e46900abaabd1a3b7c03d9ac850ff";
	logging-data="8820"; mail-complaints-to="abuse@eternal-september.org";
	posting-account="U2FsdGVkX19vqeYuqQfiSwxbzdKY7NDUTvAQPBehtII="
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (darwin)
Cancel-Lock: sha1:Pz02NHiqdQOp2Zxj77oifHny/3w=
	sha1:bwRIMqXzRcA0Cu1ekd0ch8lLLxw=
Xref: news.eternal-september.org comp.lang.ada:19651
Date: 2014-05-03T22:40:31+01:00
List-Id: <comp.lang.ada>

Natasha Kerensikova <lithiumcat@instinctive.eu> writes:

> So if I happened to need concurrent read operations (e.g. because
> sequencing them through a protected procedure is too inefficient), I
> can't use the standard containers. Is that right?

That would certainly be true for some of the Booch Components' Unbounded
forms, which cache the last-referenced element for a performance
improvement if it's re-referenced (I have no idea what evidence Grady
Booch had that that would actually help anyone!). And the way that
implementations of Ada.Containers protect against tampering might cause
problems; the GCC 4.9.0 Vectors has

   type Vector is new Controlled with record
      Elements : Elements_Access;
      Last     : Extended_Index := No_Index;
      Busy     : Natural := 0;
      Lock     : Natural := 0;
   end record;

and Busy and Lock aren't task-safe.

Of course those considerations have nothing to do with whether your
supposedly constant elements are in fact so.