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=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID,
	REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,7b69a8818c20ab9f
X-Google-Attributes: gid103376,public
From: Florian Weimer <usenet@deneb.cygnus.argh.org>
Subject: Re: Y21C Bug
Date: 2000/01/07
Message-ID: <87iu16yxv4.fsf@deneb.cygnus.argh.org>#1/1
X-Deja-AN: 569492061
References: <84nqbo$q28$1@nnrp1.deja.com> <84o0g2$u8v$1@nnrp1.deja.com>
 <84pvrs$7q1@ftp.kvaerner.com> <wccg0wfb02q.fsf@world.std.com>
 <84sltt$7s3@ftp.kvaerner.com> <84t966$be0$1@nnrp1.deja.com>
 <84vev2$7p4@ftp.kvaerner.com> <38737352.B282CC2@easystreet.com>
 <851j2q$78q1@ftp.kvaerner.com> <852dt0$vdl$1@nnrp1.deja.com>
 <wcc66x7w220.fsf@world.std.com>
Mail-Copies-To: never
Content-Type: text/plain; charset=us-ascii
X-Complaints-To: abuse@cygnus.argh.org
X-Trace: deneb.cygnus.argh.org 947241231 7677 192.168.1.2 (7 Jan 2000 10:33:51
 GMT)
Organization: Penguin on board
User-Agent: Gnus/5.0804 (Gnus v5.8.4) Emacs/20.4
Mime-Version: 1.0
Reply-To: Florian Weimer <fw@s.netic.de>
NNTP-Posting-Date: 7 Jan 2000 10:33:51 GMT
Newsgroups: comp.lang.ada
Date: 2000-01-07T10:33:51+00:00
List-Id: <comp.lang.ada>

Robert A Duff <bobduff@world.std.com> writes:

> Robert Dewar <robert_dewar@my-deja.com> writes:
> 
> > 1. The ability to declare very large areas of memory with
> > commit-on-use semantics. There are many uses of this. I have
> > the feeling that a lot of programmers still don't understand
> > commit-on-use.
> 
> Commit on use is indeed very cool.
> 
> Do you know which operating systems support it?

I think commit on use is the same thing what's called copy on write
on Linux.  For example, you can run the following program on a box
which only has some 300 MB of virtual memory (RAM + swap), and it will
`allocate' approximately 1.5 GB of `memory':

with Ada.Text_IO, Ada.Integer_Text_IO;
use Ada.Text_IO, Ada.Integer_Text_IO;
procedure Alloc_Mem is
   type Long_String is new String (1 .. 1024 * 1024);
   type Long_String_Access is access Long_String;
   LSA : array (1 .. 1500) of Long_String_Access;
   Byte_Count : Natural := 0;
begin
   for I in LSA'Range loop
      LSA (I) := new Long_String;
      Byte_Count := Byte_Count + Long_String'Size / 8;
   end loop;
   Put ("Successfully allocated ");
   Put (Byte_Count, 0);
   Put_Line (" bytes.");
exception
   when Storage_Error =>
      Put ("Allocation failure after ");
      Put (Byte_Count, 0);
      Put_Line (" bytes.");
end Alloc_Mem;

Of course, you shouldn't use an initialized allocator here. ;)