From: Robert Klemme <shortcutter@...>
Date: 2007-04-30T18:25:14+09:00
Subject: Re: Editing a text file

On 28.04.2007 20:44, barjunk wrote:
> <snip old stuff>
>> I consider Ara the definitive source especially when it comes to
>> flock'ing NFS mounted files, see for example:
>>
>> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/97211
>>
>> For the low profile solution check out
>>
>> http://ruby-doc.org/core/classes/File.html#M002576
>>
>> Kind regards
>>
>>         robert
> 
> Thanks Robert.
> 
> So if I'm editing this file, the basic idea here is to do this:
> 
>      require 'lockfile'
> 
>      Lockfile('lock', :retries => 0) do
>         # edit my file here
>       end
> 
> And that's it?  I'm assuming this will also work on a non-NFS file
> system as well.  That will do just fine.

No, I meant: the basic mechanism uses io.flock, e.g.

11:22:07 [Temp]: cat fl.rb
#!/usr/bin/ruby

id=ARGV.shift || $$

File.open("x", "a") do |io|
   puts "#{id}: Start #{Time.now}"
   io.flock(File::LOCK_EX)
   io.puts "#{id}: #{Time.now.inspect}"
   sleep 2
   io.puts "#{id}: #{Time.now.inspect}"
   puts "#{id}: End   #{Time.now}"
end

11:22:12 [Temp]: rm x; for ((i=0;i<10;++i)) do echo $i; ./fl.rb $i & 
done; sleep 30
removed `x'
0
[1] 272
1
[2] 2240
2
[3] 3568
3
[4] 2644
4
0: Start Mon Apr 30 11:22:20 +0200 2007
[5] 2688
5
2: Start Mon Apr 30 11:22:20 +0200 2007
1: Start Mon Apr 30 11:22:20 +0200 2007
[6] 2020
6
[7] 3472
7
3: Start Mon Apr 30 11:22:20 +0200 2007
[8] 3332
8
4: Start Mon Apr 30 11:22:20 +0200 2007
[9] 3788
9
[10] 3456
5: Start Mon Apr 30 11:22:20 +0200 2007
6: Start Mon Apr 30 11:22:21 +0200 2007
7: Start Mon Apr 30 11:22:21 +0200 2007
8: Start Mon Apr 30 11:22:21 +0200 2007
9: Start Mon Apr 30 11:22:21 +0200 2007
0: End   Mon Apr 30 11:22:22 +0200 2007
2: End   Mon Apr 30 11:22:24 +0200 2007
1: End   Mon Apr 30 11:22:26 +0200 2007
3: End   Mon Apr 30 11:22:28 +0200 2007
4: End   Mon Apr 30 11:22:30 +0200 2007
5: End   Mon Apr 30 11:22:32 +0200 2007
6: End   Mon Apr 30 11:22:34 +0200 2007
7: End   Mon Apr 30 11:22:36 +0200 2007
8: End   Mon Apr 30 11:22:38 +0200 2007
9: End   Mon Apr 30 11:22:40 +0200 2007
[1]   Done                    ./fl.rb $i
[2]   Done                    ./fl.rb $i
[3]   Done                    ./fl.rb $i
[4]   Done                    ./fl.rb $i
[5]   Done                    ./fl.rb $i
[6]   Done                    ./fl.rb $i
[7]   Done                    ./fl.rb $i
[8]   Done                    ./fl.rb $i
[9]-  Done                    ./fl.rb $i
[10]+  Done                    ./fl.rb $i
11:22:51 [Temp]:

 From the timings you can nicely see that exclusive locking works.

	robert