CF pushes us to ThreadPool

wfapp.cs

// https://twitter.com/noseratio/status/1597159958734217217

using System.Diagnostics;

namespace wfapp;

public partial class Form1 : Form
{
    // library code
    private static async Task LibApiAsync(Func<Task> waitForEvent)
    {
        // UI thread
        Debug.WriteLine(Thread.CurrentThread.IsThreadPoolThread);
        await waitForEvent().ConfigureAwait(false);
        // thread pool thread
        Debug.WriteLine(Thread.CurrentThread.IsThreadPoolThread);
    }

    // client code
    private async void Form1_Load(object sender, EventArgs e)
    {
        // UI thread
        Debug.WriteLine(Thread.CurrentThread.IsThreadPoolThread);
        await LibApiAsync(WaitForEvent);
        // UI thread
        Debug.WriteLine(Thread.CurrentThread.IsThreadPoolThread);
    }

    private Task WaitForEvent()
    {
        var tcs = new TaskCompletionSource();
        void OnIdle(object? s, EventArgs e)
        {
            Application.Idle -= OnIdle;
            tcs!.SetResult();
        }
        Application.Idle += OnIdle;
        return tcs.Task;
    }

    public Form1()
    {
        InitializeComponent();
    }
}