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=-0.3 required=5.0 tests=BAYES_00,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
Path: 
 border1.nntp.dca3.giganews.com!backlog3.nntp.dca3.giganews.com!border2.nntp.dca.giganews.com!nntp.giganews.com!usenet.blueworldhosting.com!feeder01.blueworldhosting.com!feeder.erje.net!eu.feeder.erje.net!news.etla.org!aioe.org!.POSTED!not-for-mail
From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Safety of unprotected concurrent operations on constant objects
Date: Sun, 4 May 2014 21:34:22 +0200
Organization: cbb software GmbH
Message-ID: <6ri4t2dzy5bt.13ew0lqyx8ox2$.dlg@40tude.net>
References: <slrnlm6mkg.i0l.lithiumcat@nat.rebma.instinctive.eu>
 <7403d130-8b42-43cd-a0f1-53ba34b46141@googlegroups.com>
 <slrnlmals8.i0l.lithiumcat@nat.rebma.instinctive.eu>
 <lya9aybkxc.fsf@pushface.org> <lk41jr$1vl$1@dont-email.me>
 <slrnlmbs1n.i0l.lithiumcat@nat.rebma.instinctive.eu>
 <6c2cd5d4-a44c-4c18-81a3-a0e87d25cd9e@googlegroups.com>
 <slrnlmcoqd.i0l.lithiumcat@nat.rebma.instinctive.eu>
 <5e8b7087-5a92-4cd7-957a-c149a381a88b@googlegroups.com>
Reply-To: mailbox@dmitry-kazakov.de
NNTP-Posting-Host: AuYlnUSfTZrfhAkRjyySpQ.user.speranza.aioe.org
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@aioe.org
User-Agent: 40tude_Dialog/2.0.15.1
X-Notice: Filtered by postfilter v. 0.8.2
X-Original-Bytes: 2276
Xref: number.nntp.dca.giganews.com comp.lang.ada:186217
Date: 2014-05-04T21:34:22+02:00
List-Id: <comp.lang.ada>

On Sun, 4 May 2014 11:30:02 -0700 (PDT), sbelmont700@gmail.com wrote:

> On Sunday, May 4, 2014 11:57:02 AM UTC-4, Natasha Kerensikova wrote:
>> 
>> How would you "surround it with a mutex"? Do you mean a procedure in a
>> 
>> procted object, or some other scheme I'm not familiar with?
> 
> begin
>    Semaphore.Lock
>    Map.Find("Something");
>    Semaphore.Unlock;
> end

Not so. Mutex should always be handled by a controlled "holder" object:

   declare
      Lock : Holder (Resource'Access); -- Seize the resource
   begin
      Map.Find("Something");
   end;    -- Release the resource

This guaranties that the resource will be released even upon an exception
propagation.

Regarding containers it is recommended to use reentrant mutexes if
operations will be extended or if you fancy re-dispatching. An
implementation of reentrant mutex can be found here:

http://www.dmitry-kazakov.de/ada/components.htm#Mutexes

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de