Re: [Rd] file.rename(): Guaranteed to be complete or not at all?

From: Henrik Bengtsson <hb_at_biostat.ucsf.edu>
Date: Wed, 02 Mar 2011 10:47:12 -0800

Thank you very much for these pointers.

In order to lower the risk for proceeding unknowingly with (3) or (4), I'll keep my post-rename tests for them (understanding that it is still not bullet proof).

/Henrik

On Tue, Mar 1, 2011 at 11:01 PM, Prof Brian Ripley <ripley_at_stats.ox.ac.uk> wrote:
> As the help says:
>
>  This is subject to the limitations of the OS's corresponding system
>  call: ....
>
> E.g. on Fedora 14 'man 2 rename' says, inter alia,
>
> 'If newpath already exists it will be atomically replaced (subject to a few
> conditions; see ERRORS below), so that there is no point at which another
> process attempting to access newpath will find it missing.
>
> However, when overwriting there will probably be a window in which both
> oldpath and newpath refer to the file being renamed.
>
> BUGS
>
> On NFS file systems, you can not assume that if the operation failed the
> file was not renamed.'
>
> and for Windows see
>
> http://msdn.microsoft.com/en-us/library/aa365240%28v=vs.85%29.aspx
>
> where R uses flags (MOVEFILE_REPLACE_EXISTING | MOVEFILE_COPY_ALLOWED |
> MOVEFILE_WRITE_THROUGH)
>
> Windows 95 was an example of an OS which could delete the 'to' file and fail
> to move 'from'.
>
> On Tue, 1 Mar 2011, Henrik Bengtsson wrote:
>
>> Hi,
>>
>> assume I have an existing file 'pathname' and I want to rename it to
>> 'pathnameN' (which does not exist).  I use:
>>
>> res <- file.rename(pathname, pathnameN);
>>
>> Is it guaranteed that:
>>
>> (1) if res == TRUE, the file now have name 'pathnameN' and there is no
>> file with name 'pathname'?
>> (2) if res == FALSE, nothing has changed?
>>
>> or could it theoretically also be the case that
>>
>> (3) there are say two identical files named 'pathname' and 'pathnameN',
>> (4) or worse, that neither exists?
>>
>> I can see how (3) could happen if the file is renamed by first using
>> file.copy() and then file.remove() while there is lack of write/delete
>> permission for the latter.
>>
>> Currently, my code asserts that (3) and (4) did not happen.  Is that
>> unnecessary - does file.rename() do that for me (regardless of OS)?
>>
>> Thanks
>>
>> Henrik
>>
>> ______________________________________________
>> R-devel_at_r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>
> --
> Brian D. Ripley,                  ripley_at_stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272866 (PA)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>



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