From: Joel VanderWerf <vjoel@...>
Date: 2008-07-11T01:16:34+09:00
Subject: Re: Killing a ruby script gracefully

M. Edward (Ed) Borasky wrote:
> 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.

Sounds like he was asking: which signals does EM handle and how...?

I would guess TERM would be handled with a graceful exit, just because 
that's fairly standard, but ask someone who knows EM better than I do.

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407