Github user JoshRosen commented on the pull request:
https://github.com/apache/spark/pull/1616#issuecomment-51018958
This uses
[FileLock](http://docs.oracle.com/javase/6/docs/api/java/nio/channels/FileLock.html)
as its locking mechanism. According to those docs (emphasis mine),
> Whether or not a lock actually prevents another program from accessing
the content of the locked region is system-dependent and therefore unspecified.
The native file-locking facilities of some systems are merely advisory, meaning
that programs must cooperatively observe a known locking protocol in order to
guarantee data integrity. On other systems native file locks are mandatory,
meaning that if one program locks a region of a file then other programs are
actually prevented from accessing that region in a way that would violate the
lock. On yet other systems, whether native file locks are advisory or mandatory
is configurable on a per-file basis. __To ensure consistent and correct
behavior across platforms, it is strongly recommended that the locks provided
by this API be used as if they were advisory locks.__
Can you comment on whether this approach is safe if we're using advisory
locks, and maybe add that comment to the source code?
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