File locking question

[Dennis Lee Bieber]

Petri Järvinen fed this fish to the penguins on Monday 14 October 2002 
12:06 am:

> 
> -lock the file with portalocker.py (LOCK_EX)
> file = open('d:\inetpub\scripts\graphs\%s.graph' % (name),'r')
> values = cPickle.load(file)
> -Unlock the file
> 
> I must closet the file and open it to write-mode. That causes the
> file-lock to be released and any process can read the dirty-values
> from file before it is locked again.
> 
> So! How can I lock the file so that closing the file woudn't release
> the lock?
>
        Can you open the file in RW mode ('r+' I believe)?

        Lock
        open(... 'r+')
        pickle.load
        seek(0)
        truncate(0)     # wipe out the old contents, just in case the
        pickle.save     # new contents would be smaller than the old
        close
        unlock

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