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SubjectRe: Lockless file reading

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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