How do I get elapsed time in milliseconds in Ruby?

Question

If I have a Time object got from :

Time.now

and later I instantiate another object with that same line, how can I see how many

Answer 1

You can add a little syntax sugar to the above solution with the following:

class Time
  def to_ms
    (self.to_f * 1000.0).to_i
  end
end

start_time = Time.now
sleep(3)
end_time = Time.now
elapsed_time = end_time.to_ms - start_time.to_ms  # => 3004

Answer 2

I think the answer is incorrectly chosen, that method gives seconds, not milliseconds.

t = Time.now.t­o_f
=> 1382471965.146

Here I suppose the floating value are the milliseconds

Answer 3

%L gives milliseconds in ruby

require 'time'
puts Time.now.strftime("%Y-%m-%dT%H:%M:%S.%L")

or

puts Time.now.strftime("%Y-%m-%d %H:%M:%S.%L")

will give you current timestamp in milliseconds.

Answer 4

The answer is something like:

t_start = Time.now
# time-consuming operation
t_end = Time.now

milliseconds = (t_start - t_end) * 1000.0

However, the Time.now approach risks to be inaccurate. I found this post by Luca Guidi:

https://blog.dnsimple.com/2018/03/elapsed-time-with-ruby-the-right-way/

system clock is constantly floating and it doesn't move only forwards. If your calculation of elapsed time is based on it, you're very likely to run into calculation errors or even outages.

So, it is recommended to use Process.clock_gettime instead. Something like:

def measure_time
  start_time = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  yield
  end_time = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  elapsed_time = end_time - start_time
  elapsed_time.round(3)
end

Example:

elapsed = measure_time do
    # your time-consuming task here:
    sleep 2.2321
end

=> 2.232