discourse/config/initializers/watch_for_restart.rb

# this is a trivial graceful restart on touch of tmp/restart. 
#
# It simply drains all the requests (waits up to 4 seconds) and issues a HUP
#  if you need a more sophisticated cycling restart for multiple thins it will need to be written
#
# This works fine for Discourse.org cause we host our app accross multiple machines, if you hosting
#  on a single machine you have a trickier problem at hand as you need to cycle the processes in order

Thread.new do 
  file = "#{Rails.root}/tmp/restart"
  old_time = File.ctime(file).to_i if File.exists? file
  wait_seconds = 4

  return if $PROGRAM_NAME !~ /thin/
  
  while true
    time = File.ctime(file).to_i if File.exists? file

    if old_time != time
      Rails.logger.info "attempting to reload #{$$} #{$PROGRAM_NAME} in #{wait_seconds} seconds"
      $shutdown = true
      sleep wait_seconds
      Rails.logger.info "restarting #{$$}" 
      Process.kill("HUP", $$) 
      return
    end

    sleep 1
  end
end