bug with os.rename in 2.4.1?
Steven D'Aprano
steven at REMOVE.THIS.cybersource.com.au
Tue Apr 28 23:00:34 EDT 2009
On Tue, 28 Apr 2009 14:30:02 -0500, Nick Craig-Wood wrote:
> t123 <tom.lukes at gmail.com> wrote:
>> It's running on solaris 9. Here is some of the code. It's actually
>> at the beginning of the job. The files are ftp'd over. The first
>> thing that happens is that the files get renamed before any processing
>> of the file. And when it fails, it always fails at the first file,
>> comm.dat. What I can't understand is why the inconsistent behavior.
>>
>> try:
>> if os.path.exists(paths.xferin_dir+'/COMM.DAT'):
>> os.rename(paths.xferin_dir+'/COMM.DAT',paths.xferin_dir+'/
>
> This code is inherently racy... What if two copies of your code started
> simultaneously? They might both run the os.path.exists but only one
> will succeed in the os.rename.
>
> You could write instead
>
> try:
> os.rename(paths.xferin_dir+'/COMM.DAT',paths.xferin_dir+'/
COMM.DAT'+'.0')
> except OSError:
> pass
>
> Which isn't racy.
The race condition is still there. The only difference is that in the
first case it fails noisily, with an exception, and in the second it
fails quietly and does nothing.
--
Steven
More information about the Python-list
mailing list