asp.net - SignalR and Browser Connection limit

Question

I made a simple app with SignalR for testing. When the page loads it calls a function on the server, that function then calls a client function that prints a message on the screen. I did that to check that both the client and server function works and SignalR communication works ok.

My problem is that if I open the same page on two different tabs (did it in Chrome), the first page loads ok, but the second page doesn't call the server's functions - ONLY if I close the first page.

So as far as I understand, their is probably a connection limitation that is related to the browser that doesn't allow SignalR to connect more then once (actually two, one for receiving and one for sending)

Update: I've find our that other tabs where open, but now I've checked it through and it allows only 4 tabs / pages to be active with connections. If I try to put the same page on a new tab no data is being sent, when I close one of the other tabs, the new tab sends the data right away.

What I wanted to know if there is any solution for that, because I want this connectivity to be available if the user decide to open the same page on two tabs or more.

I don't believe that it has anything to do with IIS, because from what I know it can accept thousands of connections.

Answer 1

This problem would be best addressed by the future Channel Messaging specification, which has not been implemented by any browsers to-date, but I managed to solve it by limiting the number of connections as described by Alex Ford and using localStorage as a message bus between tabs.

The storage event lets you propagate data between tabs while keeping a single SignalR connection open (thereby preventing connection saturation). Calling localStorage.setItem('sharedKey', sharedData) will raise the storage event in all other tabs (not the caller):

$(window).bind('storage', function (e) {
    var sharedData = localStorage.getItem('sharedKey');
    if (sharedData !== null)
        console.log(
            'A tab called localStorage.setItem("sharedData",'+sharedData+')'
        );
});

You can test if ($.connection.hub.state === 1) to determine if a given tab should notify the other tabs via localStorage (courtesy of Alex) to prevent duplicate localStorage.setItem calls.

Facebook overcomes this browser limitation by serving persistent connections over several sub-domains, but this can complicate deployment and testing.

Caveats

Old Connections: In Alex's solution, you need to be careful of Disconnect() not being called (e.g. exception), and you filling up your HubConnections bucket (or repository) with old hub connections. If the Session ID does not change (can happen), this may prevent new clients from establishing a SignalR connection even though none are active. Alternatively, timestamp new connections and have a sliding expiration to minimise potential impact.

Locking: localStorage may be subject to race conditions as it does not implement any locking as described here.

To support different types of events, you should encode an eventType in your JSON messages and test for it on the storage event.

Fallbacks

If a SignalR connection cannot be established, I fall back onto polling the server every 45 seconds to retrieve a notification count.

If you don't want to use localStorage, you can use cookies, but it's not as clean.