In article <[EMAIL PROTECTED]>,
Elmo Mäntynen <[EMAIL PROTECTED]> wrote:
> On Sat, 15 Jul 2006 23:52:10 +0200, Sybren Stuvel wrote:
>
> > Elmo Mäntynen enlightened us with:
> >> Only locally. I want to be able to read/write to a single file from
> >> multiple possibly parallel processes. Would 'touch lock' (or
> >> something like that) work reliably (this just occured to me)?
> >
> > I use a lock directory for that, os.mkdir('/var/lock/somedir').
> > If you use a file, you need two steps:
> > 1) Check whether the lock-file exists
> > 2) Create the lock-file
> >
> > This is not atomic. With a directory, creating it will fail if it
> > already exists. This means you can atomically check for the lock, and
> > if it doesn't exist already, you've immediately created it too.
> >
> > Sybren
>
> Thanks. Is that what atomic basically means?
Yes, and also "race condition". That's why Jim Segrave's
example code uses O_EXCL with open(2).
Donn Cave, [EMAIL PROTECTED]
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