ConcurrentQueue<packet> queue = new ConcurrentQueue<packet>();

    while(true){
        packet data;
        if (!queue.TryPeek(out packet)) continue;
        send(data);
        queue.TryDequeue(out data); //remove sent packet from the queue
    }

public struct packet
    {
        public byte[] data;
        public uint Length;
        public address addr;
        public string priority;
    }

while(true){
        packet data;
        if (!queue.TryPeek(out packet)) continue;
        foreach(packet x in queue)
        {
            if(x.priority == "high")
            {
                send(data);
                queue.TryDequeue(out data);
            }
        }
        send(data);
        queue.TryDequeue(out data);
    }