lookbrad.cs

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;

namespace ConsoleApp25
{
    class Program
    {
        static async Task Main(string[] args)
        {
            SynchronizationContext.SetSynchronizationContext(new MySyncContext());

            var l = new AsyncLocal<int>
            {
                Value = 10
            };

            await Task.Delay(1000);

            Console.WriteLine(l.Value);
        }
    }

    public class MySyncContext : SynchronizationContext
    {
        private readonly Thread _thread;
        private readonly BlockingCollection<(SendOrPostCallback d, object state)> _queue = new BlockingCollection<(SendOrPostCallback d, object state)>();
        public MySyncContext()
        {
            _thread = new Thread(Work) { IsBackground = true };
            _thread.Start();
        }

        private void Work(object obj)
        {
            foreach (var item in _queue.GetConsumingEnumerable())
            {
                item.d(item.state);
            }
        }

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