Measure estimated completion time of ruby script - ruby

Question

I've been running a lot of scripts lately that iterate over 10k - 300k objects, and I'm thinking of writing some code that estimates the completion time of the script (they take 20-180 minutes). I've got to imagine though that there's something out there that does this already. Is there?
To Clarify (edit):
Were I to write code to do this, it would work by measuring how long it takes to perform "the operation" on a single object, multiplying that amount of time by the number of objects left, and adding it to the current time.
Granted, this would only work in situations where you have a script involving a single loop that takes up 99% of the script's total run time, and in which you could reasonably expect to be able to calculate an semi-accurate average for each iteration of that loop. This is true of the scripts for which I'd like estimate completion time.

Answer 1

Have a look at the ruby-progressbar gem: https://github.com/jfelchner/ruby-progressbar
It generates a nice progressbar and estimates completion time (ETA):
example task: 67% |oooooooooooooooooooooo | ETA: 00:01:15

Answer 2

You can granularity measure the time of each method within your script and then sum the components as described here.

Answer 3

You let your process run, and after a set time of iterations, you measure the elapsed time. You then use that value as an estimation for the time left. This ensures that the time is always dynamically estimated according to the current task.
This example is extra verbose, like a code double whopper with triple cheese:
# Some variables for this test
iterations = 1000
probe_at = (iterations * 0.1).to_i
time_total = 0
#======================================
iterations.times do |i|
time_start = Time.now
#you could yield here if this were a function
5000.times do # <tedius task simulation>
Math.sqrt(rand(200000))
end # <end of tedious task simulation>
time_total += time_taken = Time.now - time_start
if i == probe_at
iteration_cost = (time_total / probe_at)
time_left = iteration_cost * (iterations - probe_at)
puts "Time taken (ACTUAL): #{time_total} | iteration: #{i}"
puts "Time left (ESTIMATE): #{time_left} | iteration: #{i}"
puts "Estimated total: #{time_total + time_left} | iteration: #{i}"
end
if i == 999
puts "Time taken (ACTUAL): #{time_total} | iteration: #{i}"
end
end
You could easily rewrite this into a class or a method.