A sample showing how to schedule work on a single thread

SingleThreadedScheduler.cs

using System.Collections.Concurrent;
using System.Threading.Channels;

var channel = Channel.CreateUnbounded<int>();

var syncContext = new SingleThreadedSyncContext();

syncContext.Post(async _ =>
{
    await foreach (var item in channel.Reader.ReadAllAsync())
    {
        Console.WriteLine(Environment.CurrentManagedThreadId);
    }
}, 
null);

for (int i = 0; ; i++)
{
    await channel.Writer.WriteAsync(i);
    Thread.Sleep(1000);
}


public class SingleThreadedSyncContext : SynchronizationContext
{
    private readonly BlockingCollection<(SendOrPostCallback Callback, object? State)> _queue = new();
    private readonly Thread _thread;

    public SingleThreadedSyncContext()
    {
        _thread = new(RunQueue!);
        _thread.Start();
    }

    public override void Post(SendOrPostCallback d, object? state)
    {
        _queue.Add((d, state));
    }

    private void RunQueue(object state)
    {
        SetSynchronizationContext(this);

        foreach (var (d, s) in _queue.GetConsumingEnumerable())
        {
            d(s);

            if (Current != this)
            {
                // Set the sync context in case the callback changed it
                SetSynchronizationContext(this);
            }
        }
    }
}