Class: ActiveSupport::FileUpdateChecker

Inherits:
Object
  • Object
show all
Defined in:
activesupport/lib/active_support/file_update_checker.rb

Overview

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

  • initialize which expects two parameters and one block as described below;

  • updated? which returns a boolean if there were updates in the filesystem or not;

  • execute which executes the given block on initialization and updates the counter to the latest timestamp;

  • execute_if_updated which just executes the block if it was updated;

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

Examples

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

ActionDispatch::Reloader.to_prepare do
  i18n_reloader.execute_if_updated
end

Instance Method Summary collapse

Constructor Details

#initialize(files, dirs = {}, &block) ⇒ FileUpdateChecker

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.

Implementation details

This particular implementation checks for added and updated files, but not removed files. Directories lookup are compiled to a glob for performance. Therefore, while someone can add new files to the files array after initialization (and parts of Rails do depend on this feature), adding new directories after initialization is not allowed.

Notice that other objects that implements FileUpdateChecker API may not even allow new files to be added after initialization. If this is the case, we recommend freezing the files after initialization to avoid changes that won't make effect.


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# File 'activesupport/lib/active_support/file_update_checker.rb', line 55

def initialize(files, dirs={}, &block)
  @files = files
  @glob  = compile_glob(dirs)
  @block = block
  @updated_at = nil
  @last_update_at = updated_at
end

Instance Method Details

#executeObject

Executes the given block and updates the counter to latest timestamp.


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# File 'activesupport/lib/active_support/file_update_checker.rb', line 76

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

#execute_if_updatedObject

Execute the block given if updated.


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# File 'activesupport/lib/active_support/file_update_checker.rb', line 84

def execute_if_updated
  if updated?
    execute
    true
  else
    false
  end
end

#updated?Boolean

Check if any of the entries were updated. If so, the updated_at value is cached until the block is executed via execute or execute_if_updated


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# File 'activesupport/lib/active_support/file_update_checker.rb', line 65

def updated?
  current_updated_at = updated_at
  if @last_update_at < current_updated_at
    @updated_at = updated_at
    true
  else
    false
  end
end