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Date:	Thu, 12 Mar 2009 17:44:50 +0100
Message-ID:	<9e3fd2c80903120944h5aebc094y7e461eee580e4eeb@mail.gmail.com>
Subject:	Re: Problem getting flock with timeout to work
From:	Robert Klemme <shortcutter AT googlemail DOT com>
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Hi again,

2009/3/12 Corinna Vinschen <corinna-cygwin AT cygwin DOT com>:
> On Mar 12 15:40, Robert Klemme wrote:

>> Any ideas? =A0Am I doing something wrong?
>
> On second thought, maybe I don't understand what you're expecting.
> Running the testcase on a Linux box I get this:
>
> Linux calimero 2.6.[etc]
> -rw-r--r-- 1 corinna vinschen 0 Mar 12 16:48 lock
> timeout 10
> started 1
> 3644 Thu Mar 12 16:48:48 CET 2009
> started 2
> 3644 Thu Mar 12 16:48:49 CET 2009
> waiting...
> 3644 Thu Mar 12 16:48:50 CET 2009
> 3644 Thu Mar 12 16:48:51 CET 2009
> 3644 Thu Mar 12 16:48:52 CET 2009
> 3662 Thu Mar 12 16:48:53 CET 2009
> 3662 Thu Mar 12 16:48:54 CET 2009
> 3662 Thu Mar 12 16:48:55 CET 2009
> 3662 Thu Mar 12 16:48:56 CET 2009
> 3662 Thu Mar 12 16:48:57 CET 2009
> done
>
> 9 seconds
>
> I don't see that this is different in the sense of "more correct" than
> on Cygwin.

Well, maybe your Linux is wrong, too. This is what *my* Linux (CentOS
5.2, all packages current) does:

[root AT padsw7ora01 tmp]# ~/fl-test-2.sh 1
Linux padsw7 2.6.18-92.1.22.el5 #1 SMP Tue Dec 16 12:03:43 EST 2008
i686 i686 i386 GNU/Linux
-rw-r--r-- 1 root root 0 Mar 12 17:39 lock
timeout 1
started 1 with PID 17106
17107 1 Thu Mar 12 17:39:29 CET 2009
started 2 with PID 17114
17107 2 Thu Mar 12 17:39:30 CET 2009
waiting...
17107 3 Thu Mar 12 17:39:31 CET 2009
17107 4 Thu Mar 12 17:39:32 CET 2009
17107 5 Thu Mar 12 17:39:33 CET 2009
done
[root AT padsw7ora01 tmp]#

The second flock does not start the command as I expect it to be.

I am referring to the man page of flock which says this about option -w:

Fail  (with an exit code of 1) if the lock cannot be acquired within
seconds seconds.  Decimal fractional values are allowed.

So, since the second flock obviously cannot obtain the lock in time, I
would have expected it to fail and not execute the command given.
This is at least a documentation issue as flock's behavior and
documentation do not match IMHO.

I'll attach another script which implements the other suggested scheme
with even more disturbing output:

17:31:09 tmp$ ./fl-test.sh
CYGWIN_NT-5.1 padrklemme1 1.5.25(0.156/4/2) 2008-06-12 19:34 i686 Cygwin
-rw-r--r-- 1 RKlemme Domain Users 0 Mar 12 17:31 lock
timeout 10
started 1 with PID 3160
1 1 Thu Mar 12 17:31:31 WEST 2009
started 2 with PID 1848
2 1 Thu Mar 12 17:31:32 WEST 2009
1 2 Thu Mar 12 17:31:32 WEST 2009
waiting...
2 2 Thu Mar 12 17:31:33 WEST 2009
1 3 Thu Mar 12 17:31:33 WEST 2009
2 3 Thu Mar 12 17:31:34 WEST 2009
1 4 Thu Mar 12 17:31:34 WEST 2009
2 4 Thu Mar 12 17:31:35 WEST 2009
1 5 Thu Mar 12 17:31:35 WEST 2009
2 5 Thu Mar 12 17:31:36 WEST 2009
done
17:31:37 tmp$

Zero locking at all!

On my Linux this script behaves as expected:

[root AT padsw7ora01 tmp]# ~/fl-test.sh
Linux padsw7 2.6.18-92.1.22.el5 #1 SMP Tue Dec 16 12:03:43 EST 2008
i686 i686 i386 GNU/Linux
-rw-r--r-- 1 root root 0 Mar 12 17:38 lock
timeout 10
started 1 with PID 16989
1 1 Thu Mar 12 17:38:12 CET 2009
started 2 with PID 16994
1 2 Thu Mar 12 17:38:13 CET 2009
waiting...
1 3 Thu Mar 12 17:38:14 CET 2009
1 4 Thu Mar 12 17:38:15 CET 2009
1 5 Thu Mar 12 17:38:16 CET 2009
2 1 Thu Mar 12 17:38:17 CET 2009
2 2 Thu Mar 12 17:38:18 CET 2009
2 3 Thu Mar 12 17:38:19 CET 2009
2 4 Thu Mar 12 17:38:20 CET 2009
2 5 Thu Mar 12 17:38:21 CET 2009
done

Now with timeout too short:

[root AT padsw7ora01 tmp]# ~/fl-test.sh 1
Linux padsw7 2.6.18-92.1.22.el5 #1 SMP Tue Dec 16 12:03:43 EST 2008
i686 i686 i386 GNU/Linux
-rw-r--r-- 1 root root 0 Mar 12 17:38 lock
timeout 1
started 1 with PID 17023
1 1 Thu Mar 12 17:38:25 CET 2009
started 2 with PID 17028
1 2 Thu Mar 12 17:38:26 CET 2009
flock error from 2
waiting...
2 1 Thu Mar 12 17:38:27 CET 2009
1 3 Thu Mar 12 17:38:27 CET 2009
2 2 Thu Mar 12 17:38:28 CET 2009
1 4 Thu Mar 12 17:38:28 CET 2009
2 3 Thu Mar 12 17:38:29 CET 2009
1 5 Thu Mar 12 17:38:29 CET 2009
2 4 Thu Mar 12 17:38:30 CET 2009
2 5 Thu Mar 12 17:38:31 CET 2009
done
[root AT padsw7ora01 tmp]#


Kind regards

robert

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