threads across fork Ruby demo

threads-across-fork.rb

#!/usr/bin/env ruby

# Pass 'fork' as the first argument to use Process.fork, otherwise Process.daemon is used.

do_fork = (ARGV[0] == 'fork')

thread = Thread.new do
  loop { sleep(1) }
end

puts "using Process.#{do_fork ? 'fork' : 'daemon'}"
puts "before pid = #{$$}, thread.alive? = #{thread.alive?.inspect}"

if do_fork
  pid = Process.fork
  if pid.nil?
    puts "after in child, pid = #{$$}, thread.alive? = #{thread.alive?.inspect}"
  else
    puts "after in parent, pid = #{$$}, thread.alive? = #{thread.alive?.inspect}"
  end
else
  Process.daemon(true, true)
  puts "after, pid = #{$$}, thread.alive? = #{thread.alive?.inspect}"
  exit(0)
end