class ActiveSupport::FileUpdateChecker

FileUpdateChecker specifies the API used by Rails to watch files and control reloading. The API depends on four methods:

After initialization, a call to execute_if_updated must execute the block only if there was really a change in the filesystem.

This class is used by Rails to reload the I18n framework whenever they are changed upon a new request.

i18n_reloader = ActiveSupport::FileUpdateChecker.new(paths) do
  I18n.reload!
end

ActiveSupport::Reloader.to_prepare do
  i18n_reloader.execute_if_updated
end

Public Class Methods

new(files, dirs = {}, &block) click to toggle source

It accepts two parameters on initialization. The first is an array of files and the second is an optional hash of directories. The hash must have directories as keys and the value is an array of extensions to be watched under that directory.

This method must also receive a block that will be called once a path changes. The array of files and list of directories cannot be changed after FileUpdateChecker has been initialized.

# File lib/active_support/file_update_checker.rb, line 42
def initialize(files, dirs = {}, &block)
  unless block
    raise ArgumentError, "A block is required to initialize a FileUpdateChecker"
  end

  @files = files.freeze
  @glob  = compile_glob(dirs)
  @block = block

  @watched    = nil
  @updated_at = nil

  @last_watched   = watched
  @last_update_at = updated_at(@last_watched)
end

Public Instance Methods

execute() click to toggle source

Executes the given block and updates the latest watched files and timestamp.

# File lib/active_support/file_update_checker.rb, line 80
def execute
  @last_watched   = watched
  @last_update_at = updated_at(@last_watched)
  @block.call
ensure
  @watched = nil
  @updated_at = nil
end
execute_if_updated() { || ... } click to toggle source

Execute the block given if updated.

# File lib/active_support/file_update_checker.rb, line 90
def execute_if_updated
  if updated?
    yield if block_given?
    execute
    true
  else
    false
  end
end
updated?() click to toggle source

Check if any of the entries were updated. If so, the watched and/or updated_at values are cached until the block is executed via execute or execute_if_updated.

# File lib/active_support/file_update_checker.rb, line 61
def updated?
  current_watched = watched
  if @last_watched.size != current_watched.size
    @watched = current_watched
    true
  else
    current_updated_at = updated_at(current_watched)
    if @last_update_at < current_updated_at
      @watched    = current_watched
      @updated_at = current_updated_at
      true
    else
      false
    end
  end
end

Private Instance Methods

compile_ext(array) click to toggle source
# File lib/active_support/file_update_checker.rb, line 156
def compile_ext(array)
  array = Array(array)
  return if array.empty?
  ".{#{array.join(",")}}"
end
compile_glob(hash) click to toggle source
# File lib/active_support/file_update_checker.rb, line 142
def compile_glob(hash)
  hash.freeze # Freeze so changes aren't accidentally pushed
  return if hash.empty?

  globs = hash.map do |key, value|
    "#{escape(key)}/**/*#{compile_ext(value)}"
  end
  "{#{globs.join(",")}}"
end
escape(key) click to toggle source
# File lib/active_support/file_update_checker.rb, line 152
def escape(key)
  key.gsub(",", '\,')
end
max_mtime(paths) click to toggle source

This method returns the maximum mtime of the files in paths, or nil if the array is empty.

Files with a mtime in the future are ignored. Such abnormal situation can happen for example if the user changes the clock by hand. It is healthy to consider this edge case because with mtimes in the future reloading is not triggered.

# File lib/active_support/file_update_checker.rb, line 120
def max_mtime(paths)
  time_now = Time.now
  max_mtime = nil

  # Time comparisons are performed with #compare_without_coercion because
  # AS redefines these operators in a way that is much slower and does not
  # bring any benefit in this particular code.
  #
  # Read t1.compare_without_coercion(t2) < 0 as t1 < t2.
  paths.each do |path|
    mtime = File.mtime(path)

    next if time_now.compare_without_coercion(mtime) < 0

    if max_mtime.nil? || max_mtime.compare_without_coercion(mtime) < 0
      max_mtime = mtime
    end
  end

  max_mtime
end
updated_at(paths) click to toggle source
# File lib/active_support/file_update_checker.rb, line 109
def updated_at(paths)
  @updated_at || max_mtime(paths) || Time.at(0)
end
watched() click to toggle source
# File lib/active_support/file_update_checker.rb, line 101
def watched
  @watched || begin
    all = @files.select { |f| File.exist?(f) }
    all.concat(Dir[@glob]) if @glob
    all
  end
end