FSSM based FileWatcher for Rails

1_README.md

Rails 3.2 ships with a simple FileWatcher that only reloads your app if any of the files changed.

Besides, it also provides a mechanism to hook up your own file watcher mechanism, so we can use tools like FSSM that hooks into Mac OS X fsevents. This is an example on how to hook your own mechanism (you need Rails master, soon to be Rails 3.2):

1. Copy the 2_file_watcher.rb file below to lib/file_watcher.rb

2. Add the following inside your Application in config/application.rb

   if Rails.env.development? require "file_watcher" config.file_watcher = FileWatcher end

3. Add to your Gemfile

   group :development do gem "fssm" end

4. Profit!

More information about this behavior can be read on ActiveSupport::FileUpdateChecker

Note: the approach in Rails is actually quite fast and will probably be fine for all applications out there. In fact, if you are using Windows (or any operating system that does not have filesystem events supported by FSSM), the Rails implementation is even better as it is checks for timestamps just when required instead of having a pooling thread. In other words: before using this code and adding new dependencies to your project, make sure it really makes a difference.

2_file_watcher.rb

# From: https://gist.github.com/1471391
# Copyright José Valim 2011 MIT-LICENSE

require "active_support/core_ext/array/wrap"
require "active_support/core_ext/array/extract_options"
require "fssm"

class FileWatcher
  def initialize(files, dirs={}, &block)
    @block = block
    @last_update_at = Time.at(0)
    @updated_at = Time.at(0)
    start_monitor(files, dirs) { |base, relative| update(base, relative) }
  end

  def updated?
    raise "Error on FileWatcher. FSSM thread is dead." unless @thread.alive?
    @updated_at > @last_update_at
  end

  def execute_if_updated
    if updated?
      execute
      true
    else
      false
    end
  end

  def execute
    @last_update_at = @updated_at
    @block.call
  end

  private

  def update(base, relative)
    timestamp = File.mtime(File.join(base, relative))
    @updated_at = timestamp if timestamp > @updated_at
  end

  def compile_glob(exts)
    array = Array.wrap(array)
    return "**/*" if array.empty?
    "**/*.{#{array.join(",")}}"
  end

  def start_monitor(files, dirs, &block)
    exprs = Hash.new { |h,k| h[k] = [] }

    files.each do |file|
      exprs[File.dirname(file)] << File.basename(file)
    end

    dirs.each do |dir, exts|
      exprs[dir] << compile_glob(exts)
    end

    files.freeze
    dirs.freeze

    @monitor = FSSM::Monitor.new

    exprs.each do |dir, globs|
      @monitor.path dir do
        glob "{#{globs.join(",")}}"
        update(&block)
        create(&block)
      end
    end

    @thread = Thread.new { @monitor.run }
  end
end