Source
Future<WorkerSession> createSession([initial]) async {
var s = generateBasicId(length: 25);
var session = new _WorkerSession(this, s, true, initial);
_sendPort.send({"t": "session.created", "s": s, "n": initial});
await ((_sessionReady[s] = new Completer.sync()).future);
_ourSessions[s] = session;
return session;
}