looping state

[stefano-vardanega]

Hi, I have a state machine with 2 states: Idle and Pinging.
Pinging state permits reentry, to loop the ping forever.
The problem is that when I call _Machine.Fire(Triggers.Ping), the call does not exit.

Is there a better way to handle looping states?

Here a sample code:

// See https://aka.ms/new-console-template for more information
using Stateless;

var _MachineSynch = new StateMachine<State, Triggers>(State.Idle);
_MachineSynch.Configure(State.Idle)
                .Permit(Triggers.Ping, State.Pinging)
                .OnEntry(OnDisconnect);

_MachineSynch.Configure(State.Pinging)
    .PermitReentry(Triggers.Ping)
    .Permit(Triggers.Disconnect, State.Idle)
    .OnEntry(OnPing);

void OnDisconnect()
{
    Task.Delay(100).Wait();
    Console.WriteLine("Disconnected");
}


void OnPing()
{
    Console.WriteLine("Pinging...");
    Task.Delay(1000).Wait();
    Console.WriteLine("PingED. repinging");
    _MachineSynch.Fire(Triggers.Ping);
    Console.WriteLine("PingED. repinged");
}


//start synch
_MachineSynch.Fire(Triggers.Ping);
Console.WriteLine("FIRED"); //NEVER ARRIVES HERE

public enum State
{
    Idle,
    Pinging,
}

public enum Triggers
{
    //Connect,
    Ping,
    Disconnect,
}

[felixcollins]

You are blocking the thread that is doing the work. Try using a timer to implement your ping delay. You will have to be careful to send all events to a single thread for stateless. In your example you only have one event anyway - which would be the ping timer firing.

[stefano-vardanega]

Hi, thanks for confirmation. I successfully implemented a pattern with timers indeed.

// See https://aka.ms/new-console-template for more information
using Stateless;

private readonly System.Timers.Timer? _TimerPing = new System.Timers.Timer(1000) { AutoReset = true, Enabled = false };
_TimerPing.Elapsed += async (s, e) => await OnTimerFramework(OnPing);

var _MachineSynch = new StateMachine<State, Triggers>(State.Idle);
_MachineSynch.Configure(State.Idle)
                .Permit(Triggers.Ping, State.Pinging)
                .OnEntry(OnDisconnect);

_MachineSynch.Configure(State.Pinging)
    .PermitReentry(Triggers.Ping)
    .Permit(Triggers.Disconnect, State.Idle)
    .OnEntry(() => ConfigureTimer(true, _TimerPing))
    .OnExit( () => ConfigureTimer(false, _TimerPing));

void OnDisconnect()
{
    Task.Delay(100).Wait();
    Console.WriteLine("Disconnected");
}


void OnPing()
{
    Console.WriteLine("Pinging...");
}


//start synch
_MachineSynch.Fire(Triggers.Ping);
Console.WriteLine("FIRED"); //NEVER ARRIVES HERE

public enum State
{
    Idle,
    Pinging,
}

public enum Triggers
{
    //Connect,
    Ping,
    Disconnect,
}

private void ConfigureTimer(bool active, System.Timers.Timer timer)
{
    if (timer != null)
        if (active)
        {
            timer.Start();
        }
        else
        {
            timer.Stop();
        }
}

private async Task OnTimerFramework(Func<Task> execute)
{
    if (_TimerRunning)
    {
        L("Timer already running", LogEventLevel.Verbose);
        return;
    }

    try
    {
        _TimerRunning = true;
        await execute();
    }
    catch (Exception ex)
    {
        L($"Timer general error: {ex.Message}", LogEventLevel.Error);
        if (_Machine != null)
        {
                await _Machine.FireAsync(Triggers.Disconnect);
        }
    }
    finally
    {
        _TimerRunning = false;
    }
}

[felixcollins]

I can't see the implementation of your OnTimerFrameWork method. Be aware that the timer event will be fired from a different thread to your main thread. This is not a problem if the only thing using the state machine is the timer, but if you add more events from other sources you will need a way to ensure all state machine triggers happen in the same thread. The usual solution is a queue and a dedicated thread to consume the events.

[stefano-vardanega]

I can't see the implementation of your OnTimerFrameWork method. Be aware that the timer event will be fired from a different thread to your main thread. This is not a problem if the only thing using the state machine is the timer, but if you add more events from other sources you will need a way to ensure all state machine triggers happen in the same thread. The usual solution is a queue and a dedicated thread to consume the events.

I've added the OnTimerFramework method in the code above.
The State Machine is used by everyone: Timers and GUI! 🫤 Until now it seemed to work either.

[felixcollins]

The tricky thing about concurrency bugs is that they will not show up immediately. If you are using a GUI, you could use invoke on the GUI thread and do all the state machine calls on that thread.