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From rhtyd <...@git.apache.org>
Subject [GitHub] cloudstack pull request: kvm: Aqcuire lock when running security g...
Date Wed, 27 Apr 2016 20:26:04 GMT
Github user rhtyd commented on the pull request:

    https://github.com/apache/cloudstack/pull/1408#issuecomment-215217268
  
    @wido I tested your original PR and the current updated PR, the locking never happened
on my test env (Ubuntu x64).
    
    I read the manpage, and found that when you open a file twice `flock` will treat both
FDs independently while `fcntl` (the lockf usage) treats them as FDs. This means that when
two processes could run the python script at the same time, no locking would actually occur.
    
    I wrote a test program to demonstrate this: (for testing you may replace flock with lockf
and see for yourself that it does not lock at all)
    https://gist.github.com/rhtyd/5d9983e7d58311ba8e517eefd931a507
    
    So, my suggestion is to:
    - use flock instead of lockf, assuming and likely the file exists on local filesystem
we can use `flock` with no issues
    - use the previously used open instead of with open, as with open syntax closes file when
the statements under it return


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