Implement IApplicationLifetime to detect application shutdown and gracefully close connections

[timbellomo]

Some thoughts on graceful shutdown, either for app pool recycle or server reboot. Event can fire to notify clients.

public void ConfigureServices(IServiceCollection services)
{
    services.AddSignalR();
    services.AddSingleton<IApplicationLifetime>(provider =>
    {
        var lifetime = provider.GetService<IHostApplicationLifetime>();
        return lifetime;
    });
}

then

 public void Configure(IApplicationBuilder app, IWebHostEnvironment env, IApplicationLifetime lifetime)
{
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapHub<DashboardHub>("/dashboardHub", options =>
        {
            options.AddHubOptions<DashboardHub>(o =>
            {
                o.AddClient lifetime);
            });
        });
    });
}

then

public class DashboardHub: Hub
{
    private readonly IApplicationLifetime _lifetime;
    private static CAD _cad;

    public DashboardHub(IApplicationLifetime lifetime, CAD cad)
    {
        _lifetime = lifetime;
        _lifetime.ApplicationStopping.Register(OnStopping);
        _cad = cad;
    }

    private void OnStopping()
    {
        // Code to handle the shutdown goes here
    }
}

There may be better ways to handle this.

[timbellomo]

Actually - IApplicationLifetype is obsolete; use IHostApplicationLifetime instead.