[Rails] Can I fork() in a model?

[Ara.T.Howard]

On Sat, 12 Mar 2005, LN wrote:

> Hi Everyone,
>
>  I have a long running background process that I would like to do with the
>  DB but I want the UI to return immediately.
>
>  Can I fork within model class method?  I am running under FastCGI.
>
>  How should the child process terminate itself at the end of the function?
>  is Kernel.exit! appropriate? or is plain old Kernel.exit better?  Should I
>  return a status?
>
>  My code thus far:
>
>  def self.sortBG(spec)
>
>    pid=fork
>
>    # in the parent, return now
>    if (pid)
>      Process.detach(pid)
>      return
>    end

this simply starts a thread that periodically waits for your child if that
what you want...

>
>    # in the child, go ahead with the sort.
>
>    # ... DO SOME LENGTHY PROCESSING ...
>
>    Kernel.exit!
>  end
>
>  I am experimenting now but hoped someone out there may have
> tried this already.
>
>  Thanks so much,


the biggest issue with the above is that your system will accumulate zombies
if (when - remeber the process manager) your fastcgi process exits.  i *think*
what you want to do is become a child of init: being careful not not to
generate any out/err/put... something like:

   jib:~/eg/ruby > cat dp.rb

     require 'fileutils'

     class DetachedProcess
       def initialize(*a, &b)
         @b = b
       end
       def run
         pid = fork do
           [ STDIN, STDOUT, STDERR ].each{|io| io.reopen '/dev/null', 'r+'}
           fork{ @b.call(*@a) }
           exit!
         end
         Process::waitpid pid
       end
     end

     dp =
       DetachedProcess::new do
         sleep 5
         FileUtils::touch 'when_grandchild_died'
       end

     dp.run

     puts "#{ Process::pid } exited @ #{ Time::now }"


   jib:~/eg/ruby > ruby dp.rb && sleep 5 && stat when_grandchild_died

     10021 exited @ Sat Mar 12 19:02:28 MST 2005

       File: `when_grandchild_died'
       Size: 0               Blocks: 0          IO Block: 8192   Regular File
     Device: bh/11d  Inode: 16449677    Links: 1
     Access: (0664/-rw-rw-r--)  Uid: (  447/ ahoward)   Gid: (  447/ ahoward)
     Access: 2005-03-12 19:02:33.000000000 -0700
     Modify: 2005-03-12 19:02:33.000000000 -0700
     Change: 2005-03-12 19:02:33.000000000 -0700


this won't leave behind any zombies AND you don't have to collect the exit
status directly in your app.

HTH.

kind regards.

-a
-- 
===============================================================================
| EMAIL   :: Ara [dot] T [dot] Howard [at] noaa [dot] gov
| PHONE   :: 303.497.6469
| When you do something, you should burn yourself completely, like a good
| bonfire, leaving no trace of yourself.  --Shunryu Suzuki
===============================================================================