[jcifs] Acquiring exclusive lock on a file seems to not be working anymore

[Michael B Allen]

On Tue, Aug 9, 2016 at 6:03 AM, Moritz Bechler <bechler at agno3.eu> wrote:
> Hi,
>
>
> has anyone noticed that the SmbFile.FILE_NO_SHARE option which is supposed
> to grant an exclusive lock on a file, is not working anymore?
> I wrote this small example program, which I run under windows 7 machine.
> The program basically starts 45 threads which try to append the text
> “test\n” in the same file at the same time, incrementing a counter if a
> IOException “File used by another process” occurs.
>
>
> At the end, it is expected to have the file text.txt containing N rows with
> the word “test”, and the number 45 – N printed in the console (the number of
> threads that got “File used by another process” exception).
> However, the result is different on each execution and never correct – the
> number of rows containing “test” in the test.txt file plus the number
> printed in the console is always smaller than 45, which indicates that
> locking is not working at all.
>
> Yep, there is a bug - but it's not the locking that is broken, it's
> SmbFileOutputStream's append mode. It does use
> Trans2QueryFSInformationResponse to retrieve the current file length as it
> calls SmbFile.length before opening it (which does not follow the sharing
> semantics and probably has no consistency guarantees whatsoever). Therefor
> your file pointer will be set to a stale position and you do not actually
> append but overwrite already present data. Nice.
>
> ( Patch, which may or may not apply cleanly:
> https://github.com/AgNO3/jcifs-ng/commit/022842a1685293335e918a2a1d5416cf39bccdd9
> )

Hi Moritz,

Thanks for finding this and sharing your fix. I have added this to the
TODO list. As usual no ETA for actually being applied.

Mike

-- 
Michael B Allen
Java Active Directory Integration
http://www.ioplex.com/