Question

Inspired by my own experience with multithreaded Winforms applications, as well as questions such as

• Avoiding the woes of Invoke/BeginInvoke in cross-thread WinForm event handling?
• Avoid calling Invoke when the control is disposed

I’ve come up with a very simple pattern, whose soundness I would like to verify.

Basically I’m creating (and running throughout the application’s lifetime) a BGW whose sole purpose is the synchronization of invoke requests. Consider:

public MainForm()
{
    InitializeComponent();
    InitInvocationSyncWorker();
}

private void InitInvocationSyncWorker()
{
    InvocationSync_Worker.RunWorkerAsync();
}

private void InvocationSync_Worker_DoWork(object sender, DoWorkEventArgs e)
{
    Thread.Sleep(Timeout.Infinite);
}

void InvokeViaSyncWorker(Action guiAction)
{
    InvocationSync_Worker.ReportProgress(0, guiAction);
}

private void InvocationSync_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    if (IsDisposed) return; //we're in the GUI thread now, so no race condition right?

    var action = (Action) e.UserState;
    action();
}

public void SomeMethodCalledFromAnyThread() //Sample usage
{
    InvokeViaSyncWorker(() => MyTextBox.Text = "Hello from another thread!"));    
}

Granted, it’s not the most economical of approaches (keeping a thread alive like that), but if it works and I haven’t missed anything, it sure is the simplest I’ve seen.

Feedback is highly appreciated !

Answer 1

There’s no need to open a thread just for that. Simply use SynchronizationContext, like so:

private readonly SynchronizationContext _syncContext;

public MainForm()
{
    InitializeComponent();

    _syncContext = SynchronizationContext.Current;
}

void InvokeViaSyncContext(Action uiAction)
{
    _syncContext.Post(o =>
    {
        if (IsHandleCreated && !IsDisposed) uiAction();
    }, null);
}

public void SomeMethodCalledFromAnyThread() //Sample usage
{
    InvokeViaSyncContext(() => MyTextBox.Text = "Hello from another thread!"));    
}