ReconnectSample.cs

public class ReconnectSample 
{
    private readonly HubConnection _hubConnection;
    private Task _runTask;
    private TaskCompletionSource<object> _startTcs;
    private volatile bool _stopping;

    public Task StartAsync()
    {
        _startTcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
        _runTask = RunAsync();
        return _startTcs.Task;
    }

    public Task StopAsync()
    {
        _stopping = true;
        _hubConnection.Stop();
        return _runTask;
    }

    public void ForceReconnect()
    {
        _hubConnection.Stop();
    }

    private async Task Run()
    {
        while (!_stopping)
        {
            var closeTcs = new TaskCompletionSource<object>(TaskCreationOptions.RunContinuationsAsynchronously);
            Action closedHandler = () => closeTcs.SetResult(null);

            try
            {
                _hubConnection.Closed += closedHandler;

                await _hubConnection.Start();
                // The below line could race with the client transitioning to the reconnecting state.
                //Debug.Assert(_hubConnection.State == ConnectionState.Connected);

                _startTcs.TrySetResult(null);

                // The client might auto-reconnect during this time.
                Console.WriteLine("Waiting for connection disconnect...");
                await closeTcs.Task;
            }
            catch (Exception ex)
            {
                Console.WriteLine("ConnectionError='{0}'", ex);

                // Consider varying the delay here so the clients don't flood the network all at once
                // given a wide network outage. We also want to throttle the reconnect attempts in general.
                await Task.Delay(TimeSpan.FromSeconds(5));
            }
            finally
            {
                Console.WriteLine("Connection disconnected.");
                Debug.Assert(_hubConnection.State == ConnectionState.Disconnected);

                _hubConnection.Closed -= closedHandler;
            }
        }

        Console.WriteLine("Connection stopped...");
    }
}