Concurrent writes to the same file

Neal Becker ndbecker2 at
Thu Jul 11 17:58:57 CEST 2013

Dave Angel wrote:

> On 07/11/2013 12:57 AM, Jason Friedman wrote:
>> Other than using a database, what are my options for allowing two processes
>> to edit the same file at the same time?  When I say same time, I can accept
>> delays.  I considered lock files, but I cannot conceive of how I avoid race
>> conditions.
> In general, no.  That's what a database is for.
> Now, you presumably have some reason to avoid database, but in its stead
> you have to specify some other limitations.  To start with, what do you
> mean by "the same time"?  If each process can modify the entire file,
> then there's no point in one process reading the file at all until it
> has the lock.  So the mechanism would be
>    1) wait till you can acquire the lock
>    2) open the file, read it, modify it, flush and close
>    3) release the lock
> To come up with an appropriate lock, it'd be nice to start by specifying
> the entire environment.  Which Python, which OS?  Are the two processes
> on the same CPU, what's the file system, and is it locally mounted?

You can use a seperate server process to do file I/O, taking multiple inputs 
from clients.  Like syslogd.

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