Re: parallel: This should not happen. You have found a bug.

[Ole Tange]

On Sun, Aug 11, 2013 at 11:42 PM, Linda Walsh <gnu@tlinx.org> wrote:
>
> Ole Tange wrote:
>>
>> On Sun, Aug 11, 2013 at 12:28 AM, Linda Walsh <gnu@tlinx.org> wrote:
:
>> Personally I hate introducing an unneeded variable, so I would write it
>> as:
>>
>>   parallel gunzip ::: *gz
>
> specialized syntax -- didn't know...

Consider watching the intro videos
https://www.youtube.com/playlist?list=PL284C9FF2488BC6D1 and reading
the examples: 
http://www.gnu.org/software/parallel/man.html#example__working_as_xargs__n1__argument_appending

Another good thing is that it does not use semaphores, so even if
--semaphore (i.e sem) does not work on your system, the above may.

It has the added benefit of only starting parallel once: The startup
time of GNU Parallel is around 0.3 seconds which you would pay every
time with --semaphore.

>>> * The bugid: Can't open semaphore file
>>> /home/law/.parallel/semaphores/id-2fdev2fcons1.lock: Permission denied
>>
>> Why is GNU Parallel not allowed to create
>> /home/law/.parallel/semaphores/id-2fdev2fcons1.lock?
:
> While it is running (14 minutes and climbing), it seems to be testing
> and recreating (if necessary) the semaphores directory under ".parallel".
> I created my own dir, and it stayed, but if I removed the 'semaphores'
> dir, it immediately re-created it...
> It doesn't look like it is using real semaphores...but a file interlock
> which might explain it running single threaded?

When run in --semaphore mode GNU Parallel uses hard links to create a
counting semaphore. If your filesystem does not support hard links the
behaviour is undefined - and that is likely what you see.

>> What OS is Perl running on and what file system is /home/law/.parallel
>> hosted on?
>
> CYGWIN_NT-6.1-WOW64 / NTFS
>
> (thats 32bit cygwin on 64-bit win7-sp1)...

I have no idea whether that configuration supports hard links or not.

So it is possible that --semaphore does not work on your file system.


/Ole