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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 15:13:20 -0500
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Xref: g2news1.google.com comp.lang.ada:8880 comp.lang.c++:44651
 comp.realtime:1079 comp.software-eng:4634
Date: 2005-03-08T15:13:20-05:00
List-Id: <comp.lang.ada>

Dmitry A. Kazakov wrote:

> On Tue, 08 Mar 2005 13:33:33 -0500, CTips wrote:
> 
> 
>>How easy is it to build an arena allocator in Ada?
> 
> 
> It is trivial:
> 
> type Object is ...;
> type Object_Ptr is access Object;
> for Object_Ptr'Storage_Pool use My_Arena;
> 
> Here you are:
> 
> Ptr : Object_Ptr := new Object; -- This allocates it in My_Arena

And how is My_Arena defined? Is it just a blob of memory? Or is it a 
"class" that can invoke sbrk (or whatever) when it needs to?

> 
> Note that Object can still be allocated on the stack or in any other pool:
> 
> type Object_Universal_Ptr is access all Object;
> 
> This : Object;
>             -- This allocates it on the stack
> That : Object_Universal_Ptr := new Object;
>             -- This will be in the(a) default pool (in the heap)
> 
> 
>>Given a processor with load-word-locked and store-word-conditional, how 
>>would I build an atomic increment function?
> 
> 
> Why should I have atomic increment function? Ada has native concurrency
> support. But if somebody would need that extremely low level thing as
> atomic integers, then:
> 
> 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.