Get number of listeners, clients connected to SignalR hub

Is there a way to find out the number of listeners (clients connected to a hub?)

I'm trying to run/start a task if at least one client is connected, otherwise do not start it:

[HubName("taskActionStatus")]
public class TaskActionStatus : Hub, IDisconnect
{
    static CancellationTokenSource tokenSource;

    public void GetTasksStatus(int? siteId)
    {
        tokenSource = new CancellationTokenSource();
        CancellationToken ct = tokenSource.Token;

        ITaskRepository taskRepository = UnityContainerSetup.Container.Resolve<ITaskRepository>();

        // init task for checking task statuses
        var tasksItem = new DownloadTaskItem();
        taskRepository.GetTasksStatusAsync(siteId, tasksItem, ct);

        // subscribe to event [ listener ]
        tasksItem.Changed += new EventHandler<TaskEventArgs>(UpdateTasksStatus);
    }

    public void UpdateTasksStatus(object sender, TaskEventArgs e)
    {
        Clients.updateMessages(e.Tasks);
    }

    // when browsing away from page
    public Task Disconnect()
    {
        try
        {
            tokenSource.Cancel();
        }
        catch (Exception)
        {
            //
        }

        return null;
    }
}

thanks