Using signalR to broadcast results from a timerjob? - signalr

Question

I'm just getting started with SignalR and I'm wondering if it's a good tool for the task I'm working on.
In short, I have objects with properties that change over time. A timer job runs every once in a while to update these properties. For the sake of explanation, let's say I have MilkJugs with a property "isExpired" that changes once a certain DateTime is hit.
When my timerjob hits a MilkJug and flips it to isExpired = true, I want all clients to get a notification instantly. If a client is looking at seven MilkJugs in Chrome, I want them to see all seven MilkJugs turn yellow (or something like that).
Could I use signalR to "broadcast" these notifications to the clients from the timerJob? I just ran through the chat example they have up and it seems super simple to get working... I think I could do something like this serverside:
public class ChatHub : Hub
{
public void Send(List<MilkJugUpdate> updates)
{
// Call the broadcastMessage method to update milkJugs.
Clients.All.broadcastMessage(updates);
}
}
And then clientside just iterate over the serialized array, updating the appropriate fields in my JS viewModels.
Does this sound about right?

Answer 1

You have got the basic idea there. However there are probably some improvements you could make.
Here I assume you send the message every time you run the timer job. This isn't necessary. You only really need to send a message to the clients if something changes.
Firstly you could handle the onconnected event, and send the current state of the milk jugs.
Now when you run the timer job, you only need to call send if something has changed. Then you send the message to the clients, telling them what has changed. On the clients side, the function handles the change something like the following
Server
public class ChatHub : Hub
{
public override Task OnConnected()
{
//some code here to fetch current state of jugs.
return base.OnConnected();
}
public void JugExpired(MilkJugUpdate update)
{
// Call the broadcastMessage method to update milkJugs.
Clients.All.updateJug(update);
}
}
Client
ChatHub.client.updateJug = function(update) {
// code to update jug here
}
This saves you sending messages to the client if nothing has changed.
Similarly as pointed out in another answer, you can call the client method directly from your timer job, but again, I would only recommend sending updates, rather than the entire state every time.

Answer 2

Absolutely, ShootR does this already (HTML5 multiplayer game). This is also done in the Stock Ticker Sample on nuget.
Ultimately, you can grab the hub context outside of the hub and use it to send messages:
public void MyTimerFunction(object state)
{
GlobalHost.ConnectionManager.GetHubContext<ChatHub>().Clients.All.broadcastMessage(updates);
}