From: "M. Edward (Ed) Borasky" <znmeb@...>
Date: 2008-07-10T23:40:57+09:00
Subject: Re: Killing a ruby script gracefully

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Tim Conner wrote:
> I have a Ruby script that uses Event machine to listen on a port for
> incoming data.  When data is received, the script saves it to the
> database.
> How can I kill this script gracefully?  I want to make sure that the
> data is not being processed or saved the to DB when I kill it.
> 
> script looks something like:
> 
> #!/usr/bin/env ruby
> require 'rubygems'
> require 'eventmachine'
> 
> module TestServer
>  def receive_data data
>    #Process and save data
>  end
> 
> end
> 
> EventMachine::run {
>                    $a = EventMachine::open_datagram_socket "", 1720,
> TestServer
> 
> }

I don't know about Windows, but on Linux, and most Unix-ish systems, 
when you "kill" a process, what you are actually doing is sending a 
signal to it, which the process can handle, catch or ignore. Processes 
usually have a default behavior for some signals built in. So check out 
"Signal handling" in the Pickaxe for the details. And if you have a 
Linux system, do "man kill" and "kill -l" for the low-level details.

One note: signal number 9 can not be caught or ignored on a Unix-ish 
box. So even if you write your own signal handler, anybody with the 
right privileges can send signal 9 to it and force an immediate and 
possibly data-corrupting end to your script.


-- 
M. Edward (Ed) Borasky
http://ruby-perspectives.blogspot.com/

"A mathematician is a machine for turning coffee into theorems." -- 
Alfr��d R��nyi via Paul Erd��s

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