From: ts <decoux@...>
Date: 2003-07-26T00:40:32+09:00
Subject: Re: Confused about locking a file via file.flock(File::LOCK_EX)

>>>>> "L" == Ludwigi Beethoven <aix_tech@yahoo.com> writes:

L> what I thought it will do. To test it, I wrote a
L> simple ruby piece of code that, first locks the file,
L> second spin-loop forever while I open another window
L> and vi the "locked" file. Well, I am able to vi and
L> change the file that is supposed to be locked. 

 Well, to understand the problem

svg% cat b.rb
#!/usr/bin/ruby
f = File.new("aa", "w")
f.flock(File::LOCK_EX)
puts "file locked #{Process.pid}"

fork do
   g = File.new("aa", "w")
   if !g.flock(File::LOCK_SH|File::LOCK_NB)
      puts "error : file locked #{Process.pid}"
   end
end
Process.wait

fork do
   g = File.new("aa", "w")
   g.puts "aa"
end
Process.wait
svg% 

svg% cat aa
cat: aa: No such file or directory
svg%
 
svg% b.rb
file locked 25340
error : file locked 25341
svg%
 
svg% cat aa
aa
svg% 

 a lock work *only* if the process try to acquire a lock before writing in
 the file.

 In my example, the first fork test if the file is locked and give an error
 if it can't have the lock.

 The second fork, don't test and write directly in the file (it bypass the
 lock) 

 In your case, vi do like my second fork : it don't try to acquire a lock
 and write in the file 


Guy Decoux