From: Robert Klemme <shortcutter@...>
Date: 2009-12-13T23:10:32+09:00
Subject: Re: Is it possible to force a Ruby program to run as a proc name   different than "ruby"?

On 13.12.2009 13:55, Iñaki Baz Castillo wrote:
> El Domingo, 13 de Diciembre de 2009, Robert Klemme escribió:
>> On 13.12.2009 00:51, Iñaki Baz Castillo wrote:
>>> El Sábado, 12 de Diciembre de 2009, Robert Klemme escribió:
>>>> This is what I would do:
>>>>
>>>> VAR='/var/run'
>>>>
>>>> pid_file = File.join(VAR, File.basename($0) + '.pid')
>>>>
>>>> begin
>>>>     old_pid = File.read(pid_file).to_i
>>>>     Process.kill 0, old_pid
>>>>     $stderr.puts "ERROR: already running with PID #{old_pid}"
>>>>     exit 1
>>>> rescue Errno::ENOENT
>>>>     # no pid file
>>>> rescue Errno::ESRCH
>>>>     # process not running
>>>>     $stderr.puts 'WARNING: stale pid file'
>>>> end
>>>>
>>>> # open file with EXCL in order to catch race conditions where two
>>>> # processes were started almost at the same time and both thought
>>>> # they would be a new instance.  Uncomment sleep to simulate:
>>>> # sleep 2
>>>> File.open(pid_file, File::EXCL | File::WRONLY | File::CREAT) {|io|
>>>> io.write($$)}
>>>> trap(0) {File.delete pid_file}
>>>>
>>>> puts "OK, here we go."
>>> Let me a question: is the above a fragment of a Linux init script written
>>> in Ruby (rather than bash/sh as usual)?
>> That was hacked together for demonstration purposes.  It was not
>> intended as an init script but rather as the demon itself - albeit
>> without all the demonization stuff (detaching from terminal etc.)
>> because I wanted to focus on the aspect of pid file handling and killing.
> 
> Ok ok, I just asked as curiosity because some time ago I tryed to do a init 
> script in Ruby and couldn't do it properly... not remember the reason right 
> now...

One small thing just comes to mind: you can replace the "trap(0) {..." 
with "at_exit {...".  This is probably a bit more rubyish.  It also has 
the advantage that you can have multiple at_exit handlers while you can 
only have one trap:

robert@fussel ~
$ ruby19 -e '2.times {|i| at_exit { puts "exiting #{i}..."} }'
exiting 1...
exiting 0...

robert@fussel ~
$ ruby19 -e '2.times {|i| trap(0) { puts "exiting #{i}..."} }'
exiting 1...

robert@fussel ~
$

>>> If so, according to LSB specifications it should return 0 (success) in
>>> case of "start" action when the daemon is already running.
>> Well, if you write a start script for that "ruby demon" you would have
>> to handle exit codes properly.
> 
> Ok, so later the init script could get "1" and return "0" as LSB states.

Exactly.

> Thanks a lot again.

You're welcome!

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/