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Re: O.T. optimising file placement

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On Fri, 24 Feb 2012 20:31:25 -0500, Arne Vajhøj wrote:

> On 2/23/2012 6:16 PM, Martin Gregorie wrote:
>> On Wed, 22 Feb 2012 21:40:19 -0500, Arne Vajhøj wrote:
>>> Most OS'es support async IO.
>>>
>> Yes, I know, but its not relevant to a single-threaded process since
>> its logic generally requires it to wait for a read or write to complete
>> before it continues[1]. Hence my comment that this prevents head
>> movement being optimized unless a lot of processes are active because
>> there's only one outstanding IOP per process.
>>
>> [1] unless you're deliberately doing async i/o using poll() or
>>      select() (in C) or nio (in Java), in which case the process is
>>      often best regarded as a half-way house between single and
>>      multi-threaded logic.
> 
> I am talking about deliberate not accidental async IO.
> 
> And you maybe consider it half singlethreaded half multithreaded,
> but when there is only one thread it is usually just called single
> threaded.
>
Yes, I agree that it is technically single threaded programming and 
therefore dodges a lot of problems associated with threading (especially 
in C).

Nonetheless most of the async i/o I've seen in C ends up treating 
transfers to and from a channel as a connected set of transfers, i.e. 
some context is associated with the channel and is kept distinct from 
context associated with other channels. The use of context implies having 
dedicated data storage for that channel, so from some viewpoints the 
logic of the program is indistinguishable from that used in a threaded 
approach. I can't comment about nio in Java since I haven't yet needed to 
use it.

Anyway, that's what I meant by the mongrel 'half-threaded' term.
   

-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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O.T. optimising file placement Roedy Green <see_website@mindprod.com.invalid> - 2012-02-21 09:59 -0800
  Re: O.T. optimising file placement Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-21 18:05 -0800
  Re: O.T. optimising file placement Jeff Higgins <jeff@invalid.invalid> - 2012-02-21 21:41 -0500
    Re: O.T. optimising file placement Jeff Higgins <jeff@invalid.invalid> - 2012-02-21 23:23 -0500
      Re: O.T. optimising file placement Roedy Green <see_website@mindprod.com.invalid> - 2012-02-22 11:15 -0800
        Re: O.T. optimising file placement Jeff Higgins <jeff@invalid.invalid> - 2012-02-22 16:00 -0500
          Re: O.T. optimising file placement Jeff Higgins <jeff@invalid.invalid> - 2012-02-22 16:03 -0500
            Re: O.T. optimising file placement Gene Wirchenko <genew@ocis.net> - 2012-02-22 14:52 -0800
              Re: O.T. optimising file placement Jeff Higgins <jeff@invalid.invalid> - 2012-02-22 18:24 -0500
                Re: O.T. optimising file placement Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-02-22 17:10 -0800
                Re: O.T. optimising file placement Gene Wirchenko <genew@ocis.net> - 2012-02-22 20:02 -0800
        Re: O.T. optimising file placement Lew <noone@lewscanon.com> - 2012-02-22 14:27 -0800
          Re: O.T. optimising file placement Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-23 01:31 +0000
            Re: O.T. optimising file placement Arne Vajhøj <arne@vajhoej.dk> - 2012-02-22 21:40 -0500
              Re: O.T. optimising file placement Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-23 23:16 +0000
                Re: O.T. optimising file placement Patricia Shanahan <pats@acm.org> - 2012-02-23 16:22 -0800
                Re: O.T. optimising file placement Patricia Shanahan <pats@acm.org> - 2012-02-23 21:45 -0800
                Re: O.T. optimising file placement Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-24 20:21 +0000
                Re: O.T. optimising file placement Arne Vajhøj <arne@vajhoej.dk> - 2012-02-24 20:31 -0500
                Re: O.T. optimising file placement Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-25 13:15 +0000
            Re: O.T. optimising file placement Lew <noone@lewscanon.com> - 2012-02-23 16:39 -0800
              Re: O.T. optimising file placement Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-24 01:49 +0000
                Re: O.T. optimising file placement Lew <noone@lewscanon.com> - 2012-02-24 10:50 -0800
                Re: O.T. optimising file placement Martin Gregorie <martin@address-in-sig.invalid> - 2012-02-24 23:59 +0000
              Re: O.T. optimising file placement Arne Vajhøj <arne@vajhoej.dk> - 2012-02-24 20:25 -0500
    Re: O.T. optimising file placement Roedy Green <see_website@mindprod.com.invalid> - 2012-02-22 10:54 -0800

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