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: 
 eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!news.eternal-september.org!news.eternal-september.org!feeder.eternal-september.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: Tue, 13 May 2014 21:15:23 +0200
Organization: cbb software GmbH
Message-ID: <xn1l15yyiysr$.1hs6ibcqgd1ri$.dlg@40tude.net>
References: <slrnlm6mkg.i0l.lithiumcat@nat.rebma.instinctive.eu>
 <scy9v.1071029$2N5.142769@fx05.iad> <kxy9v.109149$f85.89664@fx19.iad>
 <lyzjiw7h6c.fsf@pushface.org> <fRN9v.204655$Ng5.180587@fx17.iad>
 <t7a0jcl05g1h.11jb75b2jg1l7.dlg@40tude.net> <eT_9v.574$dr.264@fx27.iad>
 <83ha6vuynrzs.1jk08faxb8mnl.dlg@40tude.net> <xtDav.68151$7X2.15124@fx19.iad>
 <1jebi7cf92ak4.1trmstj8qi3wm.dlg@40tude.net> <zv4bv.5236$pa5.5140@fx23.iad>
 <1i6pyg077xlrv.vnwotzzgb0ut$.dlg@40tude.net> <nYobv.8538$116.7932@fx21.iad>
 <10pk27v48vhcb$.1qkf6roq2yzjn$.dlg@40tude.net> <RVObv.4489$TT7.3088@fx02.iad>
 <1qq0ryc8c4l2m.1driqwwiwwl02.dlg@40tude.net>
 <%vhcv.255737$s87.168969@fx11.iad>
 <fw1hrdv0jufx$.fetdmr8mer8o$.dlg@40tude.net> <qtqcv.27961$hv6.6727@fx17.iad>
 <30rcv.17381$Nf2.13630@fx01.iad> <lywqdpmxrx.fsf@pushface.org>
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
Xref: news.eternal-september.org comp.lang.ada:19810
Date: 2014-05-13T21:15:23+02:00
List-Id: <comp.lang.ada>

On Tue, 13 May 2014 17:46:58 +0100, Simon Wright wrote:

> Brad Moore <brad.moore@shaw.ca> writes:
> 
>> That may be why Ada has PO's in the standard, but does not provide any
>> mutex libraries like the one you suggest; They are too error
>> prone. I'd be surprised if mutexes and scope locks like the one in
>> your example wouldn't have been considered for inclusion in the
>> standard at some point during the history of Ada.  Ada does provide
>> the building blocks that programmers can create such abstractions
>> however, which programmers are then free to use as they wish.
> 
> I've several times seen Randy recommend use of the Containers as a way
> of avoiding problems with memory allocation/deallocation, and I'd have
> thought simple mutexes/locks would be just as much candidates to support
> the general user.
> 
> Are they error-prone? If Joe Programmer reinvents locking, what's the
> chance that there's something wrong with it?

Usually to mutex' seize and release there are other procedures and entries
added, e.g. when mutex is used with a container like a queue. So it is not
much advantage having them in the standard library. Then there are mutex
variations like reentrant mutexes, read-write mutexes, arrays of mutexes,
ordered mutexes (in order to prevent deadlock), global (system-wide) named
mutexes etc. This is why I am sceptical that mutexes must be in the
standard library.

Much more useful IMO would be atomic operations like atomic increment,
compare and swap, and a requirement to support pragma Atomic for every
scalar type.

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