davidfowl · October 11, 2022 02:53 · Oct 11, 2022
diff --git a/SingleThreadedScheduler.cs b/SingleThreadedScheduler.cs
@@ -0,0 +1,55 @@
+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);
+            }
+        }
+    }
+}