Saturday, June 23, 2007

Timing out Child Processes



I finally ran across a short Ruby powerpoint lecture by a CMU grad student to get me on the right track. Basically I wanted to spawn a process that me eventually killed (or disappears magically) after a certain amount of time. The answer is to use Timeout.

Here is my code. Notice I got rid of the fork.

#!/usr/bin/env ruby

require 'time'
require 'timeout'
require 'pp'


def time_cmd(command,timeout)
cmd_output = []
puts "Entering time_cmd at #{Time.now.tv_sec}"
begin
status = Timeout.timeout(timeout) do
p = IO.popen(command) do |f|
puts "pid: #{$$}"
f.each_line do |g|
cmd_output << g
system("ps aux | grep netstat")
end
system("ps aux | grep netstat")
end
end
pp status
rescue Timeout::Error
puts "\n#{command} completed at #{Time.now.tv_sec}"
return cmd_output
end
end

puts "pid: #{$$}"
puts time_cmd("netstat -dwh 1",3)
system("ps aux | grep netstat")


With the following output


franz-g4:~/dev/playin/ruby mdfranz$ ./angrytimeout.rb
pid: 3658
Entering time_cmd at 1182709241
pid: 3658
root 3659 2.2 0.0 27332 368 p2 S+ 1:20PM 0:00.01 netstat -d
root 3659 1.3 0.0 27332 368 p2 S+ 1:20PM 0:00.01 netstat -d
root 3659 0.1 0.0 27332 368 p2 S+ 1:20PM 0:00.01 netstat -d
root 3659 0.0 0.0 27332 368 p2 S+ 1:20PM 0:00.01 netstat -d

netstat -dwh 1 completed at 1182709244
input (Total) output
packets errs bytes packets errs bytes colls drops
0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0


What I still haven't figured out how to do is get the process id of what is spawned by the popen so that I could Process.kill it if I needed to. I know I have been able to do this but it must have been with the Python subprocess module. which of course is more full featured.

1 comment:

pauley_unsaturated said...

I found your post really helpful! I also found the solution to your problem at the end:

pipe = IO.popen("date")

puts "child process = #{pipe.pid}"

pipe.close

the .pid method also works inside of a block.