Unity MCP Server

using System; using System.Collections.Concurrent; using System.Threading; using UnityEditor; using UnityEngine; namespace UnityMcp { /// <summary> /// Dispatches actions from background threads to Unity's main thread. /// /// MCP tool calls arrive on the TCP background thread but most Unity APIs /// (GameObject manipulation, scene operations, etc.) must run on the main thread. /// This dispatcher queues actions and executes them during EditorApplication.update. /// /// CRITICAL: This dispatcher only works in the main Unity Editor process. /// AssetImportWorker and other batch mode processes do NOT have a functioning /// EditorApplication.update loop, so actions queued in those processes will /// NEVER execute, causing tool calls to timeout. /// </summary> public static class MainThreadDispatcher { static readonly ConcurrentQueue<Action> _queue = new ConcurrentQueue<Action>(); static bool _installed; static long _lastTickUtcTicks; static int _mainThreadId; static int _queued; static int _executed; public static bool IsInstalled => _installed; public static int MainThreadId => _mainThreadId; public static int QueuedCount => Interlocked.CompareExchange(ref _queued, 0, 0); public static int ExecutedCount => Interlocked.CompareExchange(ref _executed, 0, 0); public static void Install() { // Always re-register event handlers after domain reload // Domain reloads clear event handlers but preserve static fields _installed = true; _mainThreadId = Thread.CurrentThread.ManagedThreadId; Interlocked.Exchange(ref _lastTickUtcTicks, DateTime.UtcNow.Ticks); EditorApplication.update -= Tick; EditorApplication.update += Tick; AssemblyReloadEvents.beforeAssemblyReload -= OnBeforeReload; AssemblyReloadEvents.beforeAssemblyReload += OnBeforeReload; } static void OnBeforeReload() { Shutdown(); } public static void Shutdown() { if (!_installed) return; _installed = false; EditorApplication.update -= Tick; AssemblyReloadEvents.beforeAssemblyReload -= OnBeforeReload; while (_queue.TryDequeue(out _)) { } Interlocked.Exchange(ref _queued, 0); } public static void Enqueue(Action action) { if (action == null) return; if (!_installed) { Debug.LogWarning("[UnityMcp] MainThreadDispatcher not installed, action dropped."); return; } _queue.Enqueue(action); Interlocked.Increment(ref _queued); } static void Tick() { Interlocked.Exchange(ref _lastTickUtcTicks, DateTime.UtcNow.Ticks); var count = 0; while (count < 512 && _queue.TryDequeue(out var a)) { try { a(); } catch (Exception e) { Debug.LogException(e); } Interlocked.Decrement(ref _queued); Interlocked.Increment(ref _executed); count++; } } public static string GetStatusJson() { var now = DateTime.UtcNow; var lastTicks = Interlocked.Read(ref _lastTickUtcTicks); long ageMs; if (lastTicks <= 0) { ageMs = -1; } else { var last = new DateTime(lastTicks, DateTimeKind.Utc); ageMs = (long)Math.Max(0, (now - last).TotalMilliseconds); } return "{" + "\"installed\":" + (_installed ? "true" : "false") + "," + "\"mainThreadId\":" + _mainThreadId + "," + "\"lastTickAgeMs\":" + ageMs + "," + "\"queued\":" + Interlocked.CompareExchange(ref _queued, 0, 0) + "," + "\"executed\":" + Interlocked.CompareExchange(ref _executed, 0, 0) + "}"; } } }