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: 103376,703c4f68db81387d
X-Google-Thread: 109fba,703c4f68db81387d
X-Google-Thread: 115aec,703c4f68db81387d
X-Google-Thread: f43e6,703c4f68db81387d
X-Google-Attributes: gid103376,gid109fba,gid115aec,gidf43e6,public
X-Google-Language: ENGLISH,ASCII-7-bit
Path: 
 g2news1.google.com!news3.google.com!newsfeed.stanford.edu!sn-xit-02!sn-xit-01!sn-post-01!supernews.com!corp.supernews.com!not-for-mail
From: CTips <ctips@bestweb.net>
Newsgroups: comp.lang.ada,comp.lang.c++,comp.realtime,comp.software-eng
Subject: Re: Teaching new tricks to an old dog (C++ -->Ada)
Date: Tue, 08 Mar 2005 21:51:00 -0500
Organization: Posted via Supernews, http://www.supernews.com
Message-ID: <112sp515nirmhea@corp.supernews.com>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US;
 rv:1.7.5) Gecko/20041217
X-Accept-Language: en-us, en
MIME-Version: 1.0
References: <4229bad9$0$1019$afc38c87@news.optusnet.com.au>
   <1110032222.447846.167060@g14g2000cwa.googlegroups.com>
   <871xau9nlh.fsf@insalien.org>
   <3SjWd.103128$Vf.3969241@news000.worldonline.dk>
   <87r7iu85lf.fsf@insalien.org>   <1110052142.832650@athnrd02>
   <d0dkq6$781$1@titan.btinternet.com>
 <1110284070.410136.205090@o13g2000cwo.googlegroups.com>
 <395uqaF5rhu2mU1@individual.net> <112rs0bdr2aftdf@corp.supernews.com>
 <1inxxr988rxgg$.1w9dedak41k89.dlg@40tude.net>
 <112s1r0rf0o8nca@corp.supernews.com>
 <157t6st03yru3.124h9wuwhw9si$.dlg@40tude.net>
In-Reply-To: <157t6st03yru3.124h9wuwhw9si$.dlg@40tude.net>
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-Complaints-To: abuse@supernews.com
Xref: g2news1.google.com comp.lang.ada:8905 comp.lang.c++:44693
 comp.realtime:1098 comp.software-eng:4655
Date: 2005-03-08T21:51:00-05:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov wrote:

> On Tue, 08 Mar 2005 15:13:20 -0500, CTips wrote:
> 
> 
>>Dmitry A. Kazakov wrote:
>>
>>
>>>On Tue, 08 Mar 2005 13:33:33 -0500, CTips wrote:

>>>
>>>protected type Atomic_Integer is
>>>   procedure Increment;
>>>private
>>>   Value : Integer;
>>>end Atomic_Integer;
>>>
>>>-- Implementation
>>>protected body Atomic_Integer is
>>>   procedure Increment is
>>>   begin
>>>      Value := Value + 1;
>>>   end Increment;
>>>end Atomic_Integer;
>>>
>>
>>Will that generate:
>>   L0:
>>       lwlock temp,&Value
>>       add    temp,temp,1
>>       stwcond temp,&Value
>>       if( failed ) goto L0;
>>or will it generate something much more heavy-weight.
> 
> 
> Ask your compiler vendor. Though it wouldn't be necessarily polling. Also
> usually protected objects are not used for so utterly fine-grained mutual
> exclusion/locking. Atomic integer increment is normally just a small part
> of some larger (but not lengthy) operation   For example, placing something
> in a queue. 

Umm...can be done without locking. See wait-free/lock-free algorithms.

Therefore spinning for a lock (which probably would be the
> implementation) will likely be less expensive than some tricky guards
> attached to each and every instruction.

You *REALLY* should see what can be done with lwlock/stwcond. You'll be 
suprised how cheap synchronization can be.

> Note also that at such a low level
> it would be very difficult if possible to maintain data consistency.
> Compiler simply does not know what is related to what and will try to cope
> with the worst case scenario. 

So, what escapes does the language provide to let you do this? None?

>Protected types in Ada are to describe this
> sort of semantics. So in the end atomic integers are pretty useless, no
> matter how efficient they could be implemented.
> 

That is one reason *NOT* to learn Ada; it restricts both choices and 
thinking.