De-Interleaving logger in Rails

class DeinterleavingLogger < ActiveSupport::BufferedLogger
  def initialize(*args)
    super
    @writers = Hash.new
    @writer_guard = Mutex.new
  end

  def add_writer
    @writers[Thread.current] ||= Hash.new
    @writers[Thread.current][Fiber.current] ||= Array.new
  end

  def flush_writer
    return unless current_queue
    @writer_guard.synchronize { current_queue.each { |args, block| add_without_deinterleaving *args, &block } }
    @writers[Thread.current].delete Fiber.current
  end

  def add_with_deinterleaving(*args, &block)
    if current_queue then
      current_queue << [ args, block ]
    else
      add_without_deinterleaving *args, &block
    end
  end
  alias_method_chain :add, :deinterleaving

  private

  def current_queue
    @writers[Thread.current].try(:[], Fiber.current)
  end

  class Middleware
    def initialize(app)
      @app = app
    end

    def call(env)
      Rails.logger.add_writer
      status, headers, response = @app.call(env)
      Rails.logger.flush_writer
      return [ status, headers, response ]
    end
  end
end