Re: Atomic file data replace API

[Olaf van der Spek <olafvdspek@gmail.com>]

On Fri, Jan 7, 2011 at 8:29 PM, Thomas Bellman <bellman@nsc.liu.se> wro=
te:
> What is the visibility of the changes for other processes supposed
> to be in the meantime? =C2=A0I.e., if things happen in this order:

Should be atomic too, at close time.

> 1. Process A does fda =3D open("foo.txt", O_TRUNC|O_ATOMIC)
> 2. Process B does fdb =3D open("foo.txt", O_RDONLY)
> 3. B does read(fdb, buf, 4096)
> 4. A does write(fda, "NEW DATA\n", 9)
> 5. Process C comes in and does fdc =3D open("foo.txt", O_RDONLY)
> 6. C does read(fdc, buf, 4096)
> 7. A calls close(fda)
>
> Does B see an empty file, or does it see the old contents of
> the file?

Old file, otherwise A wouldn't be atomic.

> Does C see "NEW DATA\n", or does it see the old
> contents of the file, or perhaps an empty file?

Old file again, as the 'transaction' isn't finished until close.

--=20
Olaf
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