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!feeder.eternal-september.org!nntp-feed.chiark.greenend.org.uk!ewrotcd!newsfeed.xs3.de!io.xs3.de!news.jacob-sparre.dk!franka.jacob-sparre.dk!pnx.dk!.POSTED.rrsoftware.com!not-for-mail
From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Allocators design flaw
Date: Fri, 20 Oct 2017 20:42:45 -0500
Organization: JSA Research & Innovation
Message-ID: <ose8ml$qqi$1@franka.jacob-sparre.dk>
References: <orru6n$1hak$1@gioia.aioe.org> <orse8j$d7d$1@gioia.aioe.org>
 <ort609$1i31$2@gioia.aioe.org>
Injection-Date: Sat, 21 Oct 2017 01:42:45 -0000 (UTC)
Injection-Info: franka.jacob-sparre.dk;
 posting-host="rrsoftware.com:24.196.82.226";
	logging-data="27474"; mail-complaints-to="news@jacob-sparre.dk"
X-Priority: 3
X-MSMail-Priority: Normal
X-Newsreader: Microsoft Outlook Express 6.00.2900.5931
X-RFC2646: Format=Flowed; Original
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.7246
Xref: news.eternal-september.org comp.lang.ada:48538
Date: 2017-10-20T20:42:45-05:00
List-Id: <comp.lang.ada>

"Victor Porton" <porton@narod.ru> wrote in message 
news:ort609$1i31$2@gioia.aioe.org...
> Dmitry A. Kazakov wrote:
>
>> On 2017-10-14 04:53, Victor Porton wrote:
>>> It is impossible to properly implement an allocator through a C function
>>> (such as raptor_alloc_memory() from Raptor C library) which allocates a
>>> struct and returns the pointer to the allocated struct.
>>>
>>> It is because RM13.11(21.5/3) "The Alignment parameter is a nonzero
>>> integral multiple of D'Alignment..."
>>>
>>> (If it were "The Alignment parameter is equal to D'Alignment", then we
>>> would be able just to check (in Allocate procedure implementation) that
>>>
>>> pragma Assert(Dummy_Record'Alignment mod Alignment = 0);
>>> -- where Dummy_Record is an arbitrary C-convention record
>>> -- (as all C records have the same alignment reqs)
>>>
>>> So Alignment parameter may be arbitrarily big and the C function
>>> alignment may not conform to it.
>>
>> Usually allocators return addresses already rounded and there is nothing
>> to worry about.
>>
>>> Let us think how to work around (in Ada 202x) of this design flaw.
>>
>> If any it is _alloc_memory() flaw, not Ada's.
>
> It is an Ada flaw, because Ada must be able to interact with legacy C
> libraries.

Ada can interact just fine with C libraries. But there was never any 
intention that allocators and storage pools would be part of that 
interaction. It seems to be the case here that you are trying to fit a 
square peg into a round hole.

Keep in mind that all C interfacing is by definition implementation-defined, 
since it depends heavily on the C compiler. There's only so much portability 
that can be achieved in such interfacing; it can never be 100%.

                                Randy.