complete_signal_trap_uninterruptable.rb

def uninterruptable_operation(iteration)
  puts "[INFO #{Time.now}] Start operation, iteration #{iteration}. Part " \
    "one: Eg. we might long poll for messages here"

  sleep(5)

  puts "[INFO #{Time.now}] Operation part two. Eg. we might process " \
    "messages here."

  sleep(1)

  puts "[INFO #{Time.now}] Operation part three. Eg. we might acknowledge " \
    "the message as processed here."

  sleep(1)

  puts "[INFO #{Time.now}] Operation, iteration #{iteration}, complete."
end


# Only runs if the file is the entry point for execution,
# but not if loaded as a library
if $0 == __FILE__
  puts "[INFO #{Time.now}] #--- Starting Worker Program ---#"
  
  thread = nil
  iteration = 0

  begin
    # Main loop
    while true
      thread = Thread.new{ uninterruptable_operation(iteration) }

      # Wait for thread to complete before proceeding. Otherwise, this while
      # loop would quickly spin up the maximum number of threads all running
      # concurrently.
      thread.join
      iteration += 1
    end

  # This block only runs when the program is about to exit. It waits for
  # the running thread to complete before continuing with the exit operation
  rescue SignalException => e
    puts "[WARN #{Time.now}] #--- INTERRUPT RECEIVED ---#"
    puts "[WARN #{Time.now}] Waiting for current iteration to complete. " \
      "Interrupt again for immediate (unsafe) termination."

    # Wait for the currently running thread to exit before continuing execution
    thread.join

    puts "[INFO #{Time.now}] #--- ITERATION COMPLETED. EXITING SAFELY ---#"
  end
end