Re: Lockless file reading

From: Nagendra Singh Tomar (nagendra_tomar_at_adaptec.com)
Date: 08/27/03

  • Next message: Martin Konold: "Re: Lockless file reading" 
    Date:	Thu, 28 Aug 2003 02:45:25 +0530 (IST)
To: Timo Sirainen <tss@iki.fi>

    On Thu, 28 Aug 2003, Timo Sirainen wrote:

    > On Wed, 2003-08-27 at 21:42, Nagendra Singh Tomar wrote:
    > > Hi,
    > > I beleive ur original post was to address the case of a reader
    > reading
    > > a file getting *incorrect* data due to the file being written
    > > simultaneously by another writer process.
    >
    > Well, "old" data, which mixed with new data would become incorrect as a
    > whole.

    What is this mixing we are talking of ??

    >
    > > Why do u require file locking if there is a *single* writer ?? I don't
    >
    > > understand why a 123 written over XXX can result in 1X3. The kernel
    > should
    > > take care of this. When the writer process is writing 123 it will
    > first be
    > > written to the page cache. The page cache lock will be taken inside
    > the
    > > kernel before writing to it, so we know that writing 123 over XXX will
    > be
    > > atomic. Now even when this page is flushed to disk, the page lock
    > would
    > > be taken. So I cannot see a possibility of 123 written over XXX being
    > read
    > > as 1X3.
    >
    > That was my original plan, to just rely on such kernel behaviour. I just
    > don't know if it's such a good idea to rely on that, especially if I
    > want to keep my program portable. I'll probably fallback to that anyway
    > if my checksumming ideas won't work.

    But I don't see any problem with a single writer and >=1 reader. There is
    no question of portability.

    tomar
    >
    >

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  • Next message: Martin Konold: "Re: Lockless file reading"

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