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 milliseconds have passed? The second object may be created that same minute, over the next minutes or even hours.

Answer 1

Try subtracting the first Time.now from the second. Like so:

a = Time.now
sleep(3)
puts Time.now - a # about 3.0

This gives you a floating-point number of the seconds between the two times (and with that, the milliseconds).

Answer 2

Time.now.to_f can help you but it returns seconds.

In general, when working with benchmarks I:

• put in variable the current time;
• insert the block to test;
• put in a variable the current time, subtracting the preceding current-time value;

It's a very simple process, so I'm not sure you were really asking this...

Answer 3

As stated already, you can operate on Time objects as if they were numeric (or floating point) values. These operations result in second resolution which can easily be converted.

For example:

def time_diff_milli(start, finish)
   (finish - start) * 1000.0
end

t1 = Time.now
# arbitrary elapsed time
t2 = Time.now

msecs = time_diff_milli t1, t2

You will need to decide whether to truncate that or not.

Answer 4

ezpz's answer is almost perfect, but I hope I can add a little more.

Geo asked about time in milliseconds; this sounds like an integer quantity, and I wouldn't take the detour through floating-point land. Thus my approach would be:

irb(main):038:0> t8 = Time.now
=> Sun Nov 01 15:18:04 +0100 2009
irb(main):039:0> t9 = Time.now
=> Sun Nov 01 15:18:18 +0100 2009
irb(main):040:0> dif = t9 - t8
=> 13.940166
irb(main):041:0> (1000 * dif).to_i
=> 13940

Multiplying by an integer 1000 preserves the fractional number perfectly and may be a little faster too.

If you're dealing with dates and times, you may need to use the DateTime class. This works similarly but the conversion factor is 24 * 3600 * 1000 = 86400000 .

I've found DateTime's strptime and strftime functions invaluable in parsing and formatting date/time strings (e.g. to/from logs). What comes in handy to know is:

• The formatting characters for these functions (%H, %M, %S, ...) are almost the same as for the C functions found on any Unix/Linux system; and

• There are a few more: In particular, %L does milliseconds!