module Sass::Observer

def initialize(transport)
  @transport = transport
  @mutex = Mutex.new
  @condition_variable = ConditionVariable.new
  @error = nil
  @message = nil
  @transport.add_observer self
end

def receive_message
  @mutex.synchronize do
    @condition_variable.wait(@mutex) if @error.nil? && @message.nil?
  end
  raise @error unless @error.nil?
  @message
end

def send_message(message)
  @transport.send_message(message)
end

def update(error, message)
  @transport.delete_observer self
  @mutex.synchronize do
    @error = error
    @message = message
    @condition_variable.broadcast
  end
end