classA useful class fragment that implements['a]
engine_mixin :'a engine_state -> Unixqueue.event_system ->
object
..end
state
and
request_notification
.method state : 'a engine_state
method private set_state : 'a engine_state -> unit
method request_notification : (unit -> bool) -> unit
method private notify : unit -> unit
method event_system : Unixqueue.event_system