private void RemovePacketAwaiter(MqttPacketAwaiter packetAwaiter)
 {
     lock (_syncRoot)
     {
         _packetAwaiters.Remove(packetAwaiter);
     }
 }
 private MqttPacketAwaiter AddPacketAwaiter(Func <MqttBasePacket, bool> selector)
 {
     lock (_syncRoot)
     {
         var packetAwaiter = new MqttPacketAwaiter(selector);
         _packetAwaiters.Add(packetAwaiter);
         return(packetAwaiter);
     }
 }