Rails: Benchmark.ms deprecated

Today I stumbled upon this PR which deprecates the Benchmark.ms monkeypatch in Rails, without a replacement. It’s a handy method for instrumenting different parts of the code. Here’s how you might use it:

time_in_ms = Benchmark.ms { sleep 0.5 }
#=> 501.8

This will no longer work in Rails 8.1 (8.0 beta was just released today, so it will still work for some time). However, if you use it, you will see this deprecation warning in the logs:

`Benchmark.ms` is deprecated and will be removed in Rails 8.1 without replacement.

But if you look at the original implementation, all it does is call Benchmark.realtime, and multiply the time in seconds by 1000.

def ms(&blk)
  1000 * realtime(&blk)
end

I think the easiest way to replace it is to manually multiply by 1000 when we need the time in ms.

t = Benchmark.realtime { sleep 0.5 } #=> 0.5018...
time_in_ms = t * 1000                #=> 501.8...

Another alternative is to use ActiveSupport::Benchmark which provides a more flexible version of realtime:

time_in_ms = ActiveSupport::Benchmark.realtime(:float_millisecond) { sleep 0.5 }
#=> 501.8

I think I prefer using the first version, because the calculation is simple enough, there’s no dependency on ActiveSupport, and it’s less verbose!