On Aug 31, 8:42 am, Miles <[EMAIL PROTECTED]> wrote:
> On 8/31/07, mhearne808 wrote:
> > I have a script that will be run from a cron job once a minute. One
> > of the things this script will do is open a file to stash some
> > temporary results. I expect that this script will always finish its
> > work in less than 15 seconds, but I didn't want to depend on that.
> > Thus I started to look into file locking, which I had hoped I could
> > use in the following fashion:
>
> > Process A opens file foo
> > Process A locks file foo
> > Process A takes more than a minute to do its work
> > Process B wakes up
> > Process B determines that file foo is locked
> > Process B quits in disgust
> > Process A finishes its work
>
> That would look like (untested):
>
> importfcntl, sys
> f = open('foo', 'w+')
> try:
> fcntl.flock(f.fileno(),fcntl.LOCK_EX |fcntl.LOCK_NB)
> except IOError, e:
> if e.args[0] == 35:
> sys.exit(1)
> else:
> raise
> f.seek(0, 2) # seek to end
> # do your thing with the file
> f.flush()fcntl.flock(f.fileno(),fcntl.LOCK_UN)
> f.close()
>
> -Miles
I tested that, and it works! Thanks!
Looking at my flock(3) man page, I'm guessing that "35" is the error
code for EWOULDBLOCK. Which system header file am I supposed to look
in to figure that magic number out?
I would make the argument that this module could be either more
pythonic, or simply documented more completely. The open source
response, of course, would be "go for it!".
--Mike
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