From: Laurent Julliard <laurent@...>
Date: 2008-03-16T02:28:38+09:00
Subject: How to make net-ping thread safe?

Hi,

I'm using the excellent net-ping gem (v 1.2.2 on Ruby 1.8.6 Linux box) 
from Daniel Berger to ping a number of machines on a local area network.

I recently refactored my code to use threads and I'm having troubles 
with Net::Ping::ICMP. I'm trying to ping several machines, each one in a 
separate thread and I'm seing strange things like when one machine is on 
all three machines are reported on (although two are off). When I run my 
program with one thread only the on/off state shows as expected.

So I'm wondering if the Net::Ping::ICMP#ping method is thread safe? 
Daniel said he made no attempt to make sure that the code is and 
usggested that I post this question here.

The code for the method Net::Ping::ICMP#ping is here:
http://www.koders.com/ruby/fidE6256BC790B8AD197544CE26287B5C7D3200E4C8.aspx?s=icmp#L5

(line 61)

Here is also a simplified version of my own code:

-----------------------------------------------

require 'rubygems'
require 'net/ping/icmp'

WORK_STATIONS = ['192.168.1.1', '192.168.1.2', '192.168.1.3']
threads = []
ping_objects = []

WORK_STATIONS.each do |ip|
   ping_objects << Net::Ping::ICMP.new(ip)
   threads << Thread.new(ip, ping_objects.last) do |ip, p|
     puts "Monitoring #{ip}..."
     loop do
       puts "#{ip} is #{p.ping ? 'on' : 'off'}"
       sleep 2
     end
   end
end

threads.each { |th| th.join }

------------------------------------------------

Any advice either to change my own script or improve the net-ping code 
is welcome.

Thanks for your help!

Laurent