example in flock manpage still not useful.

example in flock manpage still not useful.

[Pierre Gaston]

I can see why the following change has been made but, as it is, it
doesn't work at all

http://git.kernel.org/?p=utils/util-linux/util-linux.git;a=commitdiff;h=c348d9346ae60b78a03d6dcd964e23fb40a625df

(
   flock -n 9
   # ... commands executed under lock ...

) 9>/var/lock/mylockfile\fP

flock -n 9 does nothing here besides testing the lock.

I suggest to revert to flock -s 9...or rather to just flock 9, since a
shared lock doesn't indeed seems very useful either here.

The example can be fixed using {   ;} instead of a subshell and adding
flock -n 9 || exit 1, but I think it doesn't match
the intention of the committer which was to show a way to avoid 2
concurrent executions of a script.

If  you want an example exiting the script, I suggest adding an example like:

exec 9>/var/lock/mylockfile  # open the file descriptor for the
duration of the script
flock -n 9 || exit 1                 # exit if the lock can't be acquire.

Pierre

Re: example in flock manpage still not useful.

[Karel Zak]

On Thu, Aug 25, 2011 at 03:26:14PM +0300, Pierre Gaston wrote:
> flock -n 9 || exit 1                 # exit if the lock can't be acquire.

 Fixed. Thanks!

    Karel

-- 
 Karel Zak  <kzak@redhat.com>
 http://karelzak.blogspot.com

Re: example in flock manpage still not useful.

[Peter Breitenlohner]

On Mon, 29 Aug 2011, Karel Zak wrote:

> On Thu, Aug 25, 2011 at 03:26:14PM +0300, Pierre Gaston wrote:
>> flock -n 9 || exit 1                 # exit if the lock can't be acquire.
>
> Fixed. Thanks!

Shouldn't that be:
         # exit if the lock can't be acquired.

Regards
Peter Breitenlohner <peb@mppmu.mpg.de>