Comments on: Single program instance http://www.insecure.ws/2009/07/28/single-program-instance Wed, 25 Aug 2010 08:27:44 +0000 hourly 1 http://wordpress.org/?v=3.0.1 By: Francesco Pretto http://www.insecure.ws/2009/07/28/single-program-instance/comment-page-1#comment-946 Francesco Pretto Sun, 28 Feb 2010 11:14:22 +0000 http://www.insecure.ws/?p=155#comment-946 Yup, I noticed the misunderstanding now. Would be cool to have a 'fcntl' command similar to 'flock', so you can have a shell scripted critical section. I workarounded this using your python script and subprocess.call('critical-section.sh', shell=True). The same can certainly be done for the fcntl C program (but don't need now, so I didn't investigate more :) . Thank you again. Yup, I noticed the misunderstanding now. Would be cool to have a ‘fcntl’ command similar to ‘flock’, so you can have a shell scripted critical section. I workarounded this using your python script and subprocess.call(‘critical-section.sh’, shell=True). The same can certainly be done for the fcntl C program (but don’t need now, so I didn’t investigate more :) .

Thank you again.

]]> By: kang http://www.insecure.ws/2009/07/28/single-program-instance/comment-page-1#comment-940 kang Thu, 25 Feb 2010 11:47:50 +0000 http://www.insecure.ws/?p=155#comment-940 you're correct about python, i haven't noticed it about flock/fnctl, it is just a misunderstanding, the flock program achieves locking (using flock) by wrapping around the script. i clarified it ;) thanks! you’re correct about python, i haven’t noticed it
about flock/fnctl, it is just a misunderstanding, the flock program achieves locking (using flock) by wrapping around the script. i clarified it ;)

thanks!

]]> By: Francesco Pretto http://www.insecure.ws/2009/07/28/single-program-instance/comment-page-1#comment-927 Francesco Pretto Thu, 11 Feb 2010 10:59:53 +0000 http://www.insecure.ws/?p=155#comment-927 Forgot: in 2) , the fp.close() in the PYTHON script. Greetings, Francesco Forgot: in 2) , the fp.close() in the PYTHON script.

Greetings,
Francesco

]]> By: Francesco Pretto http://www.insecure.ws/2009/07/28/single-program-instance/comment-page-1#comment-926 Francesco Pretto Thu, 11 Feb 2010 10:58:42 +0000 http://www.insecure.ws/?p=155#comment-926 Hello. Nice reference, but there are a couple of problems. 1) flock from util-linux is not a wrapper around fcntl() but flock(), a different and less flexible locking mechanism. This is a problem because the two mechanisms are mutually incompatible. At the moment, there's no shell wrapper for fcntl(); 2) That fp.close() should actually remove the lock before entering the critical section. If you remove it, or move it just before the os.unlink(), the code should be fine. Hello. Nice reference, but there are a couple of problems.

1) flock from util-linux is not a wrapper around fcntl() but flock(), a different and less flexible locking mechanism. This is a problem because the two mechanisms are mutually incompatible. At the moment, there’s no shell wrapper for fcntl();
2) That fp.close() should actually remove the lock before entering the critical section. If you remove it, or move it just before the os.unlink(), the code should be fine.

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