broken_current.rb

def stop
  @exit = 1
  raise "ERROR"
end

def start
  i = 0

  trap("TERM") { stop }

  loop do
    i += 1
    perform(i)
    sleep 0.1
    break if @exit
  end
end

def perform(i)
  puts "run #{i}"
  sleep 0.1
rescue RuntimeError
  puts "Got error"
end

pid = Process.pid
Thread.new do
  sleep 1
  Process.kill("TERM", pid)
end

start

proposal.rb

def stop
  raise "ERROR"
end

def start
  i = 0

  loop do
    i += 1

    begin
      trap("TERM") { stop }
      perform(i)
    rescue RuntimeError
      shutdown(i)
      break
    ensure
      trap("TERM", "DEFAULT")
    end
  end
end

def perform(n)
  puts "run #{n}"
  sleep 0.1
end

def shutdown(n)
  return if @shutdowning
  @shutdowning = true
  puts "gracefully shutdown #{n}"
end

pid = Process.pid

Thread.new do
  sleep 1
  Process.kill("TERM", pid)
end

start