HostPortPair类
+ host+ port
+ host_port_tuple()
PassThroughPlan类
+ recv()
_SendReceiveSocketPair类
+ socket_to_listen_on + close_on_selector_pipe+ socket_to_send_to+ plan+ bridge+connection_phase_number
+ start()+ run()
DelayPlan类
+data_queue+thread
+ notify_closed()+ recv()
Bridge类
+listen_on_host_port+connect_to_host_port+one_direction_plan+other_direction_plan
+ connection_setup()+ non_blocking_connection()+ bring_down_connection()+ down_up_connection()
Plan类
+ recv()+notify)closed()
