From: ara.t.howard@...
Date: 2007-03-05T04:49:44+09:00
Subject: Re: Strange interference between LSAPI, popen3 and MySQL

On Mon, 5 Mar 2007, Andreas Schwarz wrote:

> Hi,
>
> I am experiencing a very strange problem in my Rails app. I use popen3
> to execute an external program. Everything works fine in Mongrel, but
> when I use the app with LSAPI, after popen3 all MySQL queries fail with
> "Mysql::Error (MySQL server has gone away)". Once I comment out popen3
> it works fine again.
>
> Does anyone have the slightest idea about what goes wrong here?

guessing, but popen3 uses fork.  forking with and open db handle is undefined
for almost any db lib - of course people ignore this.  i did, and had all
sorts of issues.  you can read about them here

   http://www.linuxjournal.com/article/7922

i bet what happens is that the parent (rails) has setup an at_exit handler to
close the db on exit.  when popen forks and does it's thing in the child, the
child's death kills the db handle (at_exit handlers being inherited - of
course).

this shows what i'm talking about


   harp:~ > cat a.rb
   at_exit{ puts 'close connection __A__' }
   fork{ }
   Process.wait

   class Object
     alias_method '__fork__', 'fork'
     def fork *a, &b
       at_exit{ exit! }
       __fork__ *a, &b
     end
   end
   module Kernel
     alias_method '__fork__', 'fork'
     def fork *a, &b
       at_exit{ exit! }
       __fork__ *a, &b
     end
   end

   at_exit{ puts 'close connection __B__' }
   fork{ }
   Process.wait


   harp:~ > ruby a.rb
   close connection __A__


i'd try putting this


   class Object
     alias_method '__fork__', 'fork'
     def fork *a, &b
       at_exit{ exit! }
       __fork__ *a, &b
     end
   end
   module Kernel
     alias_method '__fork__', 'fork'
     def fork *a, &b
       at_exit{ exit! }
       __fork__ *a, &b
     end
   end

in environment.rb or something.  another idea, i'm grasping, is some sort of
buffer flushing thing.

you could try


   4242.times do |fd|
     begin
       IO.for_fd(fd).flush
     rescue Errno::EBADF
     end
   end

right before the popen.  wild ass guess though.

good luck.

-a
-- 
be kind whenever possible... it is always possible.
- the dalai lama