ruby-signals

#! /usr/bin/env ruby
# 
# Either `chmod +x` me or run me as `ruby ruby-signals`
total = 1000000000
index = 0
start_time = Time.now
sleep_for = 0.1

wat = <<WAT
Hi there, this shows how to instrument a long running CLI process so you
can get some more info out of it.

It's going from #{index} to #{total} with a sleep interval of #{sleep_for}s.
It will print each item it is currently handling. Great, much insight!

Hold on. There's this thing called signals you can send to each and every
UNIX program and a well behaved UNIX program will listen to them. For example
look here how unicorn uses this to handle zero downtime deploys:

      https://bogomips.org/unicorn/SIGNALS.html

So let's add this to our long running program as well. Try it,

      \033[33;5mPress Control-T\033[0m

You will now see additional information about the process. Just for bonus
I've also trapped the Interrupt signal so it displays a nicer end message.
So go ahead:

      Press Control-C

COMPUTERING BELOW
||
WAT

def humanize secs
  [[60, :seconds], [60, :minutes], [24, :hours], [1000, :days]].map{ |count, name|
    if secs > 0
      secs, n = secs.divmod(count)
      "#{n.to_i} #{name}"
    end
  }.compact.reverse.join(' ')
end

Signal.trap("INFO") do
  info_time = Time.now
  timestamp = info_time.strftime("%H:%M:%S")
  if index > 0
    remaining = total - index
    average_per_second = (info_time - start_time)/index.to_f
    remaining_time = humanize(remaining*average_per_second)
    puts "%s [R: %d | A: %.2f/s| E: %s]" % [timestamp, remaining, average_per_second, remaining_time]
  else
    puts "%s - 0 processed yet" % [timestamp]
  end

end

Signal.trap("INT") do
  puts "So long!"
  exit
end

puts wat

(0..total).lazy.each do |i|
  index = i
  STDOUT.print "#{index}\r"
  sleep sleep_for
end