C#•3mo ago

Async events firing out of expected sequence.

Obviously I've got some assumptions wrong here but my thinking was that in these sets of methods would still fire in sequence:

public async Task StopService() {
    if (this.service is null) throw new NullReferenceException();

    await this.service.StopAsync();

    this.service.Dispose();
    this.service = null;

    this.logStream?.Flush();
    this.logStream?.Dispose();
    this.logFileStream?.Dispose();

    OnPropertyChanged(nameof(ServiceRunning));
    OnPropertyChanged(nameof(CanServiceStart));
}

public async Task StopService() {
    if (this.service is null) throw new NullReferenceException();

    await this.service.StopAsync();

    this.service.Dispose();
    this.service = null;

    this.logStream?.Flush();
    this.logStream?.Dispose();
    this.logFileStream?.Dispose();

    OnPropertyChanged(nameof(ServiceRunning));
    OnPropertyChanged(nameof(CanServiceStart));
}

this.service.StopAsync() calls...

public async Task StopAsync()
{
    if (this.cancellationTokenSource is not null) await this.cancellationTokenSource.CancelAsync();
    this.listener.Stop();
    OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped.");
}

public async Task StopAsync()
{
    if (this.cancellationTokenSource is not null) await this.cancellationTokenSource.CancelAsync();
    this.listener.Stop();
    OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped.");
}

And my thinking was that StopService would halt on that await until StopAsync returned, but it must not be so because the OnMessage is firing after the dispose methods. So... something isn't right. I can probably turn StopAsync synchronous but I'd rather figure out WTF is going on here.

21 Replies

Yawnder•2mo ago

@maxmahem Does it happen if this.cancellationTokenSource is not null too? Also, are you saying OnMessage is getting called after, or that the result of OnMessage is received after? What are you basing that on?

maxmahem•2mo ago

cancellationTokenSource always has a value, the guard is just for completeness. OnMessage writes to logFileStream and I'm getting an exception that the stream is disposed. Although... hmm. I think I know what the problem was. I've changed the code here for a different reason, let me retest.

Yawnder•2mo ago

Often there is some pooling in the logging. So it might run deferred, then crash.

maxmahem•2mo ago

hmm... nope. I was calling OnMessage in a different thread for other reasons previously, thought that might be the issue but I've changed that and the problem persists. Logging is still pretty basic ATM so nothing should be defered here:

public void OnMessage(object? sender, EndPointMessage message)
{
    this.messages.Add(message);
    if (LoggingEnabled)
        this.logStream?.WriteLine($"{message.EndPoint}, {message.Time:s}, {message.Message}");
}

public void OnMessage(object? sender, EndPointMessage message)
{
    this.messages.Add(message);
    if (LoggingEnabled)
        this.logStream?.WriteLine($"{message.EndPoint}, {message.Time:s}, {message.Message}");
}

Yawnder•2mo ago

What's logStream?

maxmahem•2mo ago

FileStream sorry, I lied. StreamWriter.

Yawnder•2mo ago

Try flushing it after every writeline, just for fun (to remove that from the equation)

maxmahem•2mo ago

no joy

Yawnder•2mo ago

I'm clueless then, sorry Can you put a breakpoint with an "on count" condition to stop if there is a 2nd call to StopService? Also, what is your exception exactly? (just to double check)

maxmahem•2mo ago

ObjectDisposedException (no double entry into StopService either) It's getting triggered by this line here:

OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped.");

OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped.");

boiled goose•2mo ago

are you sure StopAsync is not being called twice?

maxmahem•2mo ago

100%

Yawnder•2mo ago

@maxmahem

    this.listener.Stop(); // <-- You stop it here, then...
    OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped.");  // Use it here?

    this.listener.Stop(); // <-- You stop it here, then...
    OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped.");  // Use it here?

Because what's disposed is this.listener right? (and it's the .LocalEndpoint that throws)

maxmahem•2mo ago

no, that's the um TcpListner different thing

Yawnder•2mo ago

But isn't it what throws the exception? Change OnMessage(this.listener.LocalEndpoint, $"{Name} Service Stopped."); to

var aa = this.listener;
var bb = aa.LocalEndpoint;
OnMessage(bb, $"{Name} Service Stopped.");

var aa = this.listener;
var bb = aa.LocalEndpoint;
OnMessage(bb, $"{Name} Service Stopped.");

If you inspect, you'll see that this.listener is what's already disposed.

maxmahem•2mo ago

no no, sorry for the confusion. OnMessage is just where it bubbles out from. The exception originates from there. It's nothing to do with the listner, I am sure. The exception tells me it's because of the Stream being disposed.

Yawnder•2mo ago

Oh, ok Do you know if it's the streamwriter or the underlying stream that's being disposed? (I know you said Stream, but I just want to confirm)

maxmahem•2mo ago

I think its still due to threading shennigangs. I did reformulate this, but looking deeper the call is still being processed on a different thread so... let me poke around at it.

Yawnder•2mo ago

Alright then! I'll have to go to bed anywyas, it's already 2:21

maxmahem•2mo ago

hmmm... no I thought it might be related to this, but it's not:

this.service.MessageReceived += (sender, message) => Dispatcher.UIThread.Post(() => OnMessage(sender, message));

this.service.MessageReceived += (sender, message) => Dispatcher.UIThread.Post(() => OnMessage(sender, message));

(same error if called without the Dispatcher)

boiled goose•2mo ago

can you put breakpoints or Debug.WriteLine entering and exiting both StopAsync and OnMessage to check that the order of the operations is what you expect?

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Async events firing out of expected sequence.