EditorApplication.delayCall invocation interval is throttled making UI sluggish. Use update instead.

Author: ignas2

src/com.unity.editor.tasks/Editor/Schedulers/MainThreadSynchronizationContext.cs

@@ -6,12 +6,22 @@ namespace Unity.Editor.Tasks
 	using Helpers;
 
 #if UNITY_EDITOR
-
+	using System.Collections.Generic;
 	using UnityEditor;
 
 	public class MainThreadSynchronizationContext: SynchronizationContext, IMainThreadSynchronizationContext
 	{
-		public MainThreadSynchronizationContext(CancellationToken token = default) { }
+		readonly Queue<Action> m_Callbacks = new Queue<Action>();
+
+		public MainThreadSynchronizationContext(CancellationToken token = default)
+		{
+			EditorApplication.update += Update;
+		}
+
+		public void Dispose()
+		{
+			EditorApplication.update -= Update;
+		}
 
 		public void Schedule(Action action)
 		{
@@ -24,10 +34,25 @@ public override void Post(SendOrPostCallback d, object state)
 			if (d == null)
 				return;
 
-			EditorApplication.delayCall += () => d(state);
+			lock (m_Callbacks)
+				m_Callbacks.Enqueue(() => d(state));
 		}
 
-		public void Dispose() {}
+		void Update()
+		{
+			Queue<Action> callbacks;
+
+			lock (m_Callbacks)
+			{
+				if (m_Callbacks.Count == 0)
+					return;
+				callbacks = new Queue<Action>(m_Callbacks);
+				m_Callbacks.Clear();
+			}
+
+			foreach (var callback in callbacks)
+				callback();
+		}
 	}
 #else
 	public class MainThreadSynchronizationContext : ThreadSynchronizationContext, IMainThreadSynchronizationContext