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Assets/Mirror/Core/Threading/ConcurrentNetworkWriterPool.cs

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+// API consistent with Microsoft's ObjectPool<T>.
+// thread safe.
+using System.Runtime.CompilerServices;
+
+namespace Mirror
+{
+    public static class ConcurrentNetworkWriterPool
+    {
+        // initial capacity to avoid allocations in the first few frames
+        // 1000 * 1200 bytes = around 1 MB.
+        public const int InitialCapacity = 1000;
+
+
+        // reuse ConcurrentPool<T>
+        // we still wrap it in NetworkWriterPool.Get/Recycle so we can reset the
+        // position before reusing.
+        // this is also more consistent with NetworkReaderPool where we need to
+        // assign the internal buffer before reusing.
+        static readonly ConcurrentPool<ConcurrentNetworkWriterPooled> pool =
+            new ConcurrentPool<ConcurrentNetworkWriterPooled>(
+                // new object function
+                () => new ConcurrentNetworkWriterPooled(),
+                // initial capacity to avoid allocations in the first few frames
+                // 1000 * 1200 bytes = around 1 MB.
+                InitialCapacity
+            );
+
+        // pool size access for debugging & tests
+        public static int Count => pool.Count;
+
+        public static ConcurrentNetworkWriterPooled Get()
+        {
+            // grab from pool & reset position
+            ConcurrentNetworkWriterPooled writer = pool.Get();
+            writer.Position = 0;
+            return writer;
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public static void Return(ConcurrentNetworkWriterPooled writer)
+        {
+            pool.Return(writer);
+        }
+    }
+}

Assets/Mirror/Core/Threading/ConcurrentNetworkWriterPool.cs.meta

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Assets/Mirror/Core/Threading/ConcurrentNetworkWriterPooled.cs

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+using System;
+
+namespace Mirror
+{
+    /// <summary>Pooled (not threadsafe) NetworkWriter used from Concurrent pool (thread safe). Automatically returned to concurrent pool when using 'using'</summary>
+    public sealed class ConcurrentNetworkWriterPooled : NetworkWriter, IDisposable
+    {
+        public void Dispose() => ConcurrentNetworkWriterPool.Return(this);
+    }
+}

Assets/Mirror/Core/Threading/ConcurrentNetworkWriterPooled.cs.meta

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Assets/Mirror/Core/Threading/ConcurrentPool.cs

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+// Pool to avoid allocations (from libuv2k)
+// API consistent with Microsoft's ObjectPool<T>.
+// concurrent for thread safe access.
+//
+// currently not in use. keep it in case we need it again.
+using System;
+using System.Collections.Concurrent;
+using System.Runtime.CompilerServices;
+
+namespace Mirror
+{
+    public class ConcurrentPool<T>
+    {
+        // Mirror is single threaded, no need for concurrent collections
+        // concurrent bag is for items who's order doesn't matter.
+        // just about right for our use case here.
+        readonly ConcurrentBag<T> objects = new ConcurrentBag<T>();
+
+        // some types might need additional parameters in their constructor, so
+        // we use a Func<T> generator
+        readonly Func<T> objectGenerator;
+
+        public ConcurrentPool(Func<T> objectGenerator, int initialCapacity)
+        {
+            this.objectGenerator = objectGenerator;
+
+            // allocate an initial pool so we have fewer (if any)
+            // allocations in the first few frames (or seconds).
+            for (int i = 0; i < initialCapacity; ++i)
+                objects.Add(objectGenerator());
+        }
+
+        // take an element from the pool, or create a new one if empty
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public T Get() => objects.TryTake(out T obj) ? obj : objectGenerator();
+
+        // return an element to the pool
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public void Return(T item) => objects.Add(item);
+
+        // count to see how many objects are in the pool. useful for tests.
+        public int Count => objects.Count;
+    }
+}

Assets/Mirror/Core/Threading/ConcurrentPool.cs.meta

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Assets/Mirror/Core/Threading/ThreadLog.cs

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+// threaded Debug.Log support (mischa 2022)
+//
+// Editor shows Debug.Logs from different threads.
+// Builds don't show Debug.Logs from different threads.
+//
+// need to hook into logMessageReceivedThreaded to receive them in builds too.
+using System.Collections.Concurrent;
+using System.Threading;
+using UnityEngine;
+
+namespace Mirror
+{
+    public static class ThreadLog
+    {
+        // queue log messages from threads
+        struct LogEntry
+        {
+            public int     threadId;
+            public LogType type;
+            public string  message;
+            public string  stackTrace;
+
+            public LogEntry(int threadId, LogType type, string message, string stackTrace)
+            {
+                this.threadId = threadId;
+                this.type = type;
+                this.message = message;
+                this.stackTrace = stackTrace;
+            }
+        }
+
+        // ConcurrentQueue allocations are fine here.
+        // logs allocate anywway.
+        static readonly ConcurrentQueue<LogEntry> logs =
+            new ConcurrentQueue<LogEntry>();
+
+        // main thread id
+        static int mainThreadId;
+
+#if !UNITY_EDITOR
+        // Editor as of Unity 2021 does log threaded messages.
+        // only builds don't.
+        // do nothing in editor, otherwise we would log twice.
+        // before scene load ensures thread logs are all caught.
+        // otherwise some component's Awake may be called before we hooked it up.
+        // for example, ThreadedTransport's early logs wouldn't be caught.
+        [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.BeforeSceneLoad)]
+        static void Initialize()
+        {
+
+            // set main thread id
+            mainThreadId = Thread.CurrentThread.ManagedThreadId;
+
+            // receive threaded log calls
+            Application.logMessageReceivedThreaded -= OnLog; // remove old first. TODO unnecessary?
+            Application.logMessageReceivedThreaded += OnLog;
+
+            // process logs on main thread Update
+            NetworkLoop.OnLateUpdate -= OnLateUpdate; // remove old first. TODO unnecessary?
+            NetworkLoop.OnLateUpdate += OnLateUpdate;
+
+            // log for debugging
+            Debug.Log("ThreadLog initialized.");
+        }
+#endif
+
+        static bool IsMainThread() =>
+            Thread.CurrentThread.ManagedThreadId == mainThreadId;
+
+        // callback runs on the same thread where the Debug.Log is called.
+        // we can use this to buffer messages for main thread here.
+        static void OnLog(string message, string stackTrace, LogType type)
+        {
+            // only enqueue messages from other threads.
+            // otherwise OnLateUpdate main thread logging would be enqueued
+            // as well, causing deadlock.
+            if (IsMainThread()) return;
+
+            // queue for logging from main thread later
+            logs.Enqueue(new LogEntry(Thread.CurrentThread.ManagedThreadId, type, message, stackTrace));
+        }
+
+        static void OnLateUpdate()
+        {
+            // process queued logs on main thread
+            while (logs.TryDequeue(out LogEntry entry))
+            {
+                switch (entry.type)
+                {
+                    // add [Thread#] prefix to make it super obvious where this log message comes from.
+                    // some projects may see unexpected messages that were previously hidden,
+                    // since Unity wouldn't log them without ThreadLog.cs.
+                    case LogType.Log:
+                        Debug.Log($"[Thread{entry.threadId}] {entry.message}\n{entry.stackTrace}");
+                        break;
+                    case LogType.Warning:
+                        Debug.LogWarning($"[Thread{entry.threadId}] {entry.message}\n{entry.stackTrace}");
+                        break;
+                    case LogType.Error:
+                        Debug.LogError($"[Thread{entry.threadId}] {entry.message}\n{entry.stackTrace}");
+                        break;
+                    case LogType.Exception:
+                        Debug.LogError($"[Thread{entry.threadId}] {entry.message}\n{entry.stackTrace}");
+                        break;
+                    case LogType.Assert:
+                        Debug.LogAssertion($"[Thread{entry.threadId}] {entry.message}\n{entry.stackTrace}");
+                        break;
+                }
+            }
+        }
+    }
+}

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Assets/Mirror/Core/Threading/WorkerThread.cs

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+// worker thread for Unity (mischa 2022)
+// thread with proper exception handling, profling, init, cleanup, etc. for Unity.
+// use this from main thread.
+using System;
+using System.Diagnostics;
+using System.Threading;
+using UnityEngine.Profiling;
+using Debug = UnityEngine.Debug;
+
+namespace Mirror
+{
+    public class WorkerThread
+    {
+        readonly Thread thread;
+
+        protected volatile bool active;
+
+        // stopwatch so we don't need to use Unity's Time (engine independent)
+        readonly Stopwatch watch = new Stopwatch();
+
+        // callbacks need to be set after constructor.
+        // inheriting classes can't pass their member funcs to base ctor.
+        // don't set them while the thread is running!
+        // -> Tick() returns a bool so it can easily stop the thread
+        //    without needing to throw InterruptExceptions or similar.
+        public Action Init;
+        public Func<bool> Tick;
+        public Action Cleanup;
+
+        public WorkerThread(string identifier)
+        {
+            // start the thread wrapped in safety guard
+            // if main application terminates, this thread needs to terminate too
+            thread = new Thread(
+                () => Guard(identifier)
+            );
+            thread.IsBackground = true;
+        }
+
+        public void Start()
+        {
+            // only if thread isn't already running
+            if (thread.IsAlive)
+            {
+                Debug.LogWarning("WorkerThread is still active, can't start it again.");
+                return;
+            }
+
+            active = true;
+            thread.Start();
+        }
+
+        // signal the thread to stop gracefully.
+        // returns immediately, but the thread may take a while to stop.
+        // may be overwritten to clear more flags like 'computing' etc.
+        public virtual void SignalStop() => active = false;
+
+        // wait for the thread to fully stop
+        public bool StopBlocking(float timeout)
+        {
+            // only if alive
+            if (!thread.IsAlive) return true;
+
+            // double precision for long running servers.
+            watch.Restart();
+
+            // signal to stop
+            SignalStop();
+
+            // wait while thread is still alive
+            while (IsAlive)
+            {
+                // simply wait..
+                Thread.Sleep(0);
+
+                // deadlock detection
+                if (watch.Elapsed.TotalSeconds >= timeout)
+                {
+                    // force kill all threads as last resort to stop them.
+                    // return false to indicate deadlock.
+                    Interrupt();
+                    return false;
+                }
+            }
+            return true;
+        }
+
+        public bool IsAlive => thread.IsAlive;
+
+        // signal an interrupt in the thread.
+        // this function is very safe to use.
+        // https://stackoverflow.com/questions/5950994/thread-abort-vs-thread-interrupt
+        //
+        // note this does not always kill the thread:
+        // "If this thread is not currently blocked in a wait, sleep, or join
+        //  state, it will be interrupted when it next begins to block."
+        // https://docs.microsoft.com/en-us/dotnet/api/system.threading.thread.interrupt?view=net-6.0
+        //
+        // in other words, "while (true) {}" wouldn't throw an interrupt exception.
+        // and that's _okay_. using interrupt is safe & best practice.
+        // => Unity still aborts deadlocked threads on script reload.
+        // => and we catch + warn on AbortException.
+        public void Interrupt() => thread.Interrupt();
+
+        // thread constructor needs callbacks.
+        // always define them, and make them call actions.
+        // those can be set at any time.
+        void OnInit()    => Init?.Invoke();
+        bool OnTick()    => Tick?.Invoke() ?? false;
+        void OnCleanup() => Cleanup?.Invoke();
+
+        // guarded wrapper for thread code.
+        // catches exceptions which would otherwise be silent.
+        // shows in Unity profiler.
+        // etc.
+        public void Guard(string identifier)
+        {
+            try
+            {
+                // log when work begins = thread starts.
+                // very important for debugging threads.
+                Debug.Log($"{identifier}: started.");
+
+                // show this thread in Unity profiler
+                Profiler.BeginThreadProfiling("Mirror Worker Threads", $"{identifier}");
+
+                // run init once
+                OnInit();
+
+                // run thread func while active
+                while (active)
+                {
+                    // Tick() returns a bool so it can easily stop the thread
+                    // without needing to throw InterruptExceptions or similar.
+                    if (!OnTick()) break;
+                }
+            }
+            // Thread.Interrupt() will gracefully raise a InterruptedException.
+            catch (ThreadInterruptedException)
+            {
+                Debug.Log($"{identifier}: interrupted. That's okay.");
+            }
+            // Unity domain reload will cause a ThreadAbortException.
+            // for example, when saving a changed script while in play mode.
+            catch (ThreadAbortException)
+            {
+                Debug.LogWarning($"{identifier}: aborted. This may happen after domain reload. That's okay.");
+            }
+            catch (Exception e)
+            {
+                Debug.LogException(e);
+            }
+            finally
+            {
+                // run cleanup (if any)
+                active = false;
+                OnCleanup();
+
+                // remove this thread from Unity profiler
+                Profiler.EndThreadProfiling();
+
+                // log when work ends = thread terminates.
+                // very important for debugging threads.
+                // 'finally' to log no matter what (even if exceptions)
+                Debug.Log($"{identifier}: ended.");
+            }
+        }
+    }
+}

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