Newbie question regarding threads and system commands

Ruby
1

Sorry if I’m bothering you all again… This is my first program that
runs
a) threads and b) system commands, so I apologize for being a newbie.
What
I’m trying to do is ping multiple parts of a site to help an tech
support
guy (me) in figuring out where a point of failure is at a remote
location.
The reason I’m using threads: I want it to be faster than me typing
across
multiple cmd windows. The problem: it’s taking 15+ seconds when it
works.
I’ve been tinkering now with it for a few days, and I either get the
program
to end in 1 second (killing the child threads before they are done) or I
get
the 15 second problem. I’m just not real sure where to put the
Thread.jointo make this run smoothly - nor am I sure that
thread.join is the solution.

Joel VanderWerf suggested mapping stuff, but I’m not doing this by IP
address (his solution the other day involved ping 192.168.1.#{i}) and I
couldn’t quite figure out how to modify his code to fit mine.

code (with some stuff obfuscated)

def pingsite(site, type)
result = ping -n 4 #{site}-#{type}-1.chomp
return result
end
puts “What site?”
sitelocation = gets.chomp
t0 = Time.now
data = “”
sitetype=[“something”, “somethingelse”, “again”, “more”, “otherstuff”]
sitetype.each do |type|
type=Thread.new do
puts pingsite(sitelocation, type)
end
type.join
end
#sitetype.join
t1 = Time.now
puts “Finished in #{t1 - t0} seconds”

Output:
Finished in 14.711 seconds

with sitetype.join uncommented and type.join commented, I get this:
What site?
0110
Finished in 1.051 seconds

Can someone explain to me what I’m doing wrong?

2

This is one possible solution, which seems to work fine (it takes 3.14
seconds on my system to ping 3 web sites). Bottom line: you need to keep
a list of the threads and join all of them in the calling code. Hope
this helps. I recommend that you get a copy of the “Pickaxe” book
(Programming Ruby: The Pragmatic Programmers Guide, 2nd edition) , which
has a very good section on threading and lots of examples. In the
meantime, you can read this from the first edition:

http://www.rubycentral.com/book/tut_threads.html

require ‘thread’

class SystemExecutor

Returns array [[cmd, response], [cmd, response], …]

def SystemExecutor.run(system_cmd_list)
thread_list = []
system_response_list = []
srl_mutex = Mutex.new

system_cmd_list.each do |cmd|
  thread_list << Thread.new do
    begin
      response = %x{ #{cmd} }
      srl_mutex.synchronize do
        system_response_list << [cmd, response]
      end
    rescue Exception => exc
      srl_mutex.synchronize do
        system_response_list << [cmd, exc]
      end
    end
  end
end

thread_list.each { |thr| thr.join }
system_response_list

end
end

puts “Starting ping”
start_time = Time.now
resp = SystemExecutor.run([‘ping www.ruby-forum.org’, ‘ping
www.sourceforge.net’, ‘ping www.google.com’])
elapsed_time = Time.now - start_time

resp.each do |cmd, resp|
puts “Command: #{cmd}”, ‘-’ * 20
puts “Response:\n”, ‘-’ * 20, “#{resp}”
end

puts “Elapsed time: #{elapsed_time} seconds.”

3

Maybe there’s something wrong with my system here at work then…
because
this took 11.something seconds to run on my machine. I’ll test again
from
home (both xp pro systems)

4

As it turns out, your program runs fine (<4 seconds) if I change the
ping
destinations to something on the internal network. Looks like a router
is
misconfigured somewhere. Thanks!