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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Maximum Number Of Tasks?
Date: Tue, 12 Nov 2013 21:04:12 +0100
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Date: 2013-11-12T21:04:12+01:00
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Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> mockturtle writes:
>> On Tuesday, November 12, 2013 10:53:53 AM UTC+1, FritzVonBraun wrote:
>>> I was wondering about the maximum number of tasks in Ada but I couldnt 
>>> find any info. The question is, is a task in Ada technically similar to 
>>> a thread in Windows under the hood? Threads are restricted by the stack 
>>> size that each thread has reserved, so in practice the maximum number of 
>>> threads is about 2000.
>>> 
>>
>> I remember that I saw at FOSDEM 2013 in the "Ada Developer Room" a
>> demo that plotted a Mandelbrot set by using a matrix of tasks.  A
>> participant asked then "can you do that with 10_000 tasks?"  The size
>> of the matrix was changed to 100 x 100 and everything worked smoothly;
>> so, in that case you could create at least 10_000 tasks.  The PC was a
>> laptop running some kind of Linux + GNAT, if I remember correctly.
>>
>> Riccardo
>
> Yes, you remember correctly; I was the one doing that demo :)
>
> That's because the Linux kernel allocates virtual address space to each
> task but does not allocate any physical memory (RAM or swap) unless and
> until the task writes to memory (i.e. creates variables on its stack).
> Even then, Linux only allocates the pages actually written to, not the
> full 2 MiB (or whatever the default is) per task.
>
> After the demo, I re-ran the program at home and saw it allocate 19.8
> GiB of virtual address space (I re-checked just now) and thought: gosh
> am I lucky I've been running 64-bit Linux since 2006 :)

Oh and by the way, I will introduce task pools in my demo at FOSDEM 2014
:)

-- 
Ludovic Brenta.