Asp.Net: send SignalR message on Application_End

Question

I have a standard Web Forms application that includes a SignalR hub for JavaScript clients. The hub itself works fine and messages are being sent and received as expected.

When the application is terminated (usually via application pool recycling), I want to send a specific message to all connected SignalR clients. So I hooked into Global.asax's Application_End like this:

void Application_End(object sender, EventArgs e)
{
            var hubNotifyTask = Task.Factory.StartNew(() =>
            {
                 IHubContext context = GlobalHost.ConnectionManager.GetHubContext<SiteMasterJsClientHub>();
                 context.Clients.Group("Group with all users").OnServerStartup("any message");
            });
}

Well...this doesn't work. If i put the code outside of Application_End, it works and the clients receive the message. My guess is that SignalR auto-detects the application shutdown and terminates all connections. I haven't found any documentation to verify that though.

So my question is: how can I send an automatic SignalR message just before the application shuts down?

Have you added RouteTable.Routes.MapHubs(); to your Application_Start? — Rithik Banerjee
My routing config looks different; but the hub in general works. I am using if for other things where it works fine. Just the application end message doesnt work. — Cleo
Okay then try this method sendNotificationWeekly() in camelCasing. — Rithik Banerjee
Please share your method OnServerStartup in hub class SiteMasterJsClientHub — Rithik Banerjee
As I have said before: the code works outside of Application_End. I can call OnServerStartup manually and the client will receive the message and execute the code for it. — Cleo

Durga Prasad Durga Prasad · Accepted Answer · 2020-07-13T18:30:50

Maybe you can try IRegisteredObject present in System.Web.Hosting namespace.

First we create an object that implements IRegisteredObject interface and register it with ASP.NET hosting environment by calling HostingEnvironment.RegisterObject. With that in place when the app domain is about to unloaded, the ASP.NET hosting environment will call the Stop method implementation of IRegisteredObject.

Create a class TerminationCommand which implements IRegisteredObject

public class TerminationCommand : IRegisteredObject
{
    private readonly IHubContext siteMasterJsClientHub;
    public TerminationCommand()
    {
        siteMasterJsClientHub = GlobalHost.ConnectionManager.GetHubContext<SiteMasterJsClientHub>();
    }

    public void Stop(bool immediate)
    {
        siteMasterJsClientHub.Clients.Group("Group with all users").OnServerStartup("any message");
        HostingEnvironment.UnregisterObject(this);
    }
}

Next we need to register our TerminationCommand class in Application_Start section

protected void Application_Start()
{
    //Existing code.
    HostingEnvironment.RegisterObject(new TerminationCommand());
}

References

IRegisteredObject

HostingEnvironment.Registered method

Asp.Net: send SignalR message on Application_End

1 Answers