Quit and suspend a ruby process for debugging

1-work.rb

require 'bundler/setup'
require 'rbtrace'
require 'English'

$run = true 
Signal.trap('HUP') { $run = false }

while $run do
  puts "pid=#{$PID} time=#{Time.now}"
  sleep 10
end

puts 'done'

2-run-work

$ ruby work.rb
pid=24203 time=2017-03-08 15:10:00 -0500
pid=24203 time=2017-03-08 15:10:10 -0500
done
waiting...
I can debug this process all day

3-debug-work-process

$ rbtrace --pid=24203 --eval='at_exit { $do_not_exit = true; puts "waiting..."; while $do_not_exit do sleep 1 end }'
*** attached to process 24203
>> at_exit { $do_not_exit = true; puts "waiting..."; while $do_not_exit do sleep 1 end }
=> #<Proc:0x007ffe0899cb78@(eval):1>
*** detached from process 24203

$ kill -HUP 24203

$ rbtrace --pid=24203 --eval='puts "I can debug this process all day"'
*** attached to process 24203
>> puts "I can debug this process all day"
=> nil
*** detached from process 24203

$ rbtrace --pid=24203 --eval='$do_not_exit = false'
*** attached to process 24203
*** timed out waiting for eval response
*** process 24203 is gone