GSoC'15 Proof of Concept

Autoreloading based on events VS standard Rails autoreloading

This application is meant to demonstrate the performance (lack of it) of Rails standard automatic file reloading when working with multiple files. It as well presents a raw implementation of an event-based autoreloading system and compares both approaches.

For this purpose I generated a bunch of folders and files in lib/rails_autoload. Their contents look like this:

module Foo_1
  class Bar
    def self.inspect
      "I'm Foo 1"
    end
  end
end

In the .env file there is a switch for toggling the autoreload mechanism that will be used on the lib/rails_autoload folder when the server is started.

• FS_EVENTS=false - this one just adds an entry to config.autoload_paths
• FS_EVENTS=true - when the flag is set to "true", the listen gem will be initialized and set to listen all the modification events that will come from the lib/rails_autoload folder and its subfolders. This happens in initializers/evented_reloader.rb. There is also a callback that is set for file-modification events. What it does is just load the code from the file that triggered the event.

In order to test this whole thing I created a route /foo which renders the text returned by Foo_1::Bar.inspect. Therefore, after starting a server it is possible to see the live file autoreloading by modifying the code in /lib/rails_autoload/foo_1/bar.rb and refreshing the page. It works for both autoreloading mechanisms.

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Now that we have the possibility to switch between the standard autoreloading technique and the one based on file-system events, let's see which one performs better. For this purpose I created a rake task (rake profile:rails_autoreload) that performs 100 requests on /foo, first without modifying any files inbetween the requests, and then 100 more but this time calling FileUtils#touch on a file before each request in order to make Rails to reload this file.

This procedures are benchmarked and here are the results I have got for different settings in the .env file:

• For FS_EVENTS=false

                                     user     system      total        real
no file modifications:           0.070000   0.020000   0.090000 (  4.042461)
autoreloading modified files:    0.070000   0.020000   0.090000 (  5.292976)

• For FS_EVENTS=true

                                     user     system      total        real
no file modifications:           0.070000   0.020000   0.090000 (  0.684484)
autoreloading modified files:    0.080000   0.030000   0.110000 (  0.866244)

As we can see, reloading files based on events gives us a performance boost during development.