Why is My Async Timer Blocking the UI Thread?

Question

I have a timer setup in my mainwindow code behind that fires every ten seconds. Because some of the code referenced in the timer_Elapsed event is somewhat CPU intensive I have placed it inside an await Task.Run(() => , however the UI thread continues to hang momentarily whenever the elapsed event runs. Any ideas why this would be blocking the UI? Code:

async void _timer_Elapsed(object sender, ElapsedEventArgs e)
    {
        await Task.Run(() =>
        {
            //Update default status bar text routinely
            try
            {
                if (ChecEnabled())
                {
                    this.Dispatcher.Invoke(() =>
                    {
                        StatusText.Text = String.Format("Status: Enabled. Watching for changes…");
                    });
                }
                else
                {
                    this.Dispatcher.Invoke(() =>
                    {
                        StatusText.Text = String.Format("Status: Disabled");
                    });
                }
            }
            catch (ObjectDisposedException)
            {
                //Window closed and disposed timer on different thread
            }

            //System Checks
            UpdateSystemReadyStatus();
        });
    }

Answer 1

Update your Invoke to InvokeAsync . Also, do you really need to entire method wrapped in a Task ?

async void _timer_Elapsed(object sender, ElapsedEventArgs e)
{
    //Update default status bar text routinely
    try
    {
        if (ChecEnabled())
        {
            await this.Dispatcher.InvokeAsync(() =>
            {
                StatusText.Text = String.Format("Status: Enabled. Watching for changes…");
            });
        }
        else
        {
            await this.Dispatcher.InvokeAsync(() =>
            {
                StatusText.Text = String.Format("Status: Disabled");
            });
        }
    }
    catch (ObjectDisposedException)
    {
        //Window closed and disposed timer on different thread
    }

    //System Checks
    await Task.Run(()=>UpdateSystemReadyStatus());
}