Implement speculative translation on the CPU (#515)

* Implement speculative translation on the cpu, and change the way how branches to unknown or untranslated addresses works

* Port t0opt changes and other cleanups

* Change namespace from translation related classes to ChocolArm64.Translation, other minor tweaks

* Fix typo

* Translate higher quality code for indirect jumps aswell, and on some cases that were missed when lower quality (tier 0) code was available

* Remove debug print

* Remove direct argument passing optimization, and enable tail calls for BR instructions

* Call delegates directly with Callvirt rather than calling Execute, do not emit calls for tier 0 code

* Remove unused property

* Rename argument on ArmSubroutine delegate

10 files changed, 621 insertions, 73 deletions

diff --git a/ChocolArm64/Translation/ILEmitterCtx.cs b/ChocolArm64/Translation/ILEmitterCtx.cs
index b5ebff75..ef63e60c 100644
--- a/ChocolArm64/Translation/ILEmitterCtx.cs
+++ b/ChocolArm64/Translation/ILEmitterCtx.cs
@@ -11,6 +11,7 @@ namespace ChocolArm64.Translation
     class ILEmitterCtx
     {
         private TranslatorCache _cache;
+        private TranslatorQueue _queue;
 
         private Dictionary<long, ILLabel> _labels;
 
@@ -23,6 +24,8 @@ namespace ChocolArm64.Translation
         public Block    CurrBlock => _currBlock;
         public OpCode64 CurrOp    => _currBlock?.OpCodes[_opcIndex];
 
+        public TranslationTier Tier { get; }
+
         public Aarch32Mode Mode { get; } = Aarch32Mode.User; //TODO
 
         private Dictionary<Block, ILBlock> _visitedBlocks;
@@ -47,11 +50,14 @@ namespace ChocolArm64.Translation
         private const int VecTmp1Index    = -5;
         private const int VecTmp2Index    = -6;
 
-        public ILEmitterCtx(TranslatorCache cache, Block graph)
+        public ILEmitterCtx(TranslatorCache cache, TranslatorQueue queue, TranslationTier tier, Block graph)
         {
             _cache     = cache ?? throw new ArgumentNullException(nameof(cache));
+            _queue     = queue ?? throw new ArgumentNullException(nameof(queue));
             _currBlock = graph ?? throw new ArgumentNullException(nameof(graph));
 
+            Tier = tier;
+
             _labels = new Dictionary<long, ILLabel>();
 
             _visitedBlocks = new Dictionary<Block, ILBlock>();
@@ -243,6 +249,16 @@ namespace ChocolArm64.Translation
             return new ILBlock();
         }
 
+        public void TranslateAhead(long position, ExecutionMode mode = ExecutionMode.Aarch64)
+        {
+            if (_cache.TryGetSubroutine(position, out TranslatedSub sub) && sub.Tier != TranslationTier.Tier0)
+            {
+                return;
+            }
+
+            _queue.Enqueue(new TranslatorQueueItem(position, mode, TranslationTier.Tier1));
+        }
+
         public bool TryOptEmitSubroutineCall()
         {
             if (_currBlock.Next == null)
@@ -265,20 +281,8 @@ namespace ChocolArm64.Translation
                 EmitLdarg(index);
             }
 
-            foreach (Register reg in subroutine.SubArgs)
-            {
-                switch (reg.Type)
-                {
-                    case RegisterType.Flag:   Ldloc(reg.Index, IoType.Flag);   break;
-                    case RegisterType.Int:    Ldloc(reg.Index, IoType.Int);    break;
-                    case RegisterType.Vector: Ldloc(reg.Index, IoType.Vector); break;
-                }
-            }
-
             EmitCall(subroutine.Method);
 
-            subroutine.AddCaller(_subPosition);
-
             return true;
         }
 
@@ -463,7 +467,12 @@ namespace ChocolArm64.Translation
             _ilBlock.Add(new ILOpCodeBranch(ilOp, label));
         }
 
-        public void Emit(string text)
+        public void EmitFieldLoad(FieldInfo info)
+        {
+            _ilBlock.Add(new ILOpCodeLoadField(info));
+        }
+
+        public void EmitPrint(string text)
         {
             _ilBlock.Add(new ILOpCodeLog(text));
         }
@@ -618,14 +627,9 @@ namespace ChocolArm64.Translation
             EmitCall(objType.GetMethod(mthdName, BindingFlags.Instance | BindingFlags.NonPublic));
         }
 
-        public void EmitCall(MethodInfo mthdInfo)
+        public void EmitCall(MethodInfo mthdInfo, bool isVirtual = false)
         {
-            if (mthdInfo == null)
-            {
-                throw new ArgumentNullException(nameof(mthdInfo));
-            }
-
-            _ilBlock.Add(new ILOpCodeCall(mthdInfo));
+            _ilBlock.Add(new ILOpCodeCall(mthdInfo ?? throw new ArgumentNullException(nameof(mthdInfo)), isVirtual));
         }
 
         public void EmitLdc_I(long value)
diff --git a/ChocolArm64/Translation/ILMethodBuilder.cs b/ChocolArm64/Translation/ILMethodBuilder.cs
index 70d9a2db..892f831b 100644
--- a/ChocolArm64/Translation/ILMethodBuilder.cs
+++ b/ChocolArm64/Translation/ILMethodBuilder.cs
@@ -26,72 +26,30 @@ namespace ChocolArm64.Translation
             _subName  = subName;
         }
 
-        public TranslatedSub GetSubroutine()
+        public TranslatedSub GetSubroutine(TranslationTier tier)
         {
             LocalAlloc = new LocalAlloc(_ilBlocks, _ilBlocks[0]);
 
-            List<Register> subArgs = new List<Register>();
-
-            void SetArgs(long inputs, RegisterType baseType)
-            {
-                for (int bit = 0; bit < 64; bit++)
-                {
-                    long mask = 1L << bit;
-
-                    if ((inputs & mask) != 0)
-                    {
-                        subArgs.Add(GetRegFromBit(bit, baseType));
-                    }
-                }
-            }
-
-            SetArgs(LocalAlloc.GetIntInputs(_ilBlocks[0]), RegisterType.Int);
-            SetArgs(LocalAlloc.GetVecInputs(_ilBlocks[0]), RegisterType.Vector);
-
-            DynamicMethod method = new DynamicMethod(_subName, typeof(long), GetArgumentTypes(subArgs));
+            DynamicMethod method = new DynamicMethod(_subName, typeof(long), TranslatedSub.FixedArgTypes);
 
             Generator = method.GetILGenerator();
 
-            TranslatedSub subroutine = new TranslatedSub(method, subArgs);
-
-            int argsStart = TranslatedSub.FixedArgTypes.Length;
+            TranslatedSub subroutine = new TranslatedSub(method, tier);
 
             _locals = new Dictionary<Register, int>();
 
             _localsCount = 0;
 
-            for (int index = 0; index < subroutine.SubArgs.Count; index++)
-            {
-                Register reg = subroutine.SubArgs[index];
-
-                Generator.EmitLdarg(index + argsStart);
-                Generator.EmitStloc(GetLocalIndex(reg));
-            }
+            new ILOpCodeLoadState(_ilBlocks[0]).Emit(this);
 
             foreach (ILBlock ilBlock in _ilBlocks)
             {
                 ilBlock.Emit(this);
             }
 
-            return subroutine;
-        }
-
-        private Type[] GetArgumentTypes(IList<Register> Params)
-        {
-            Type[] fixedArgs = TranslatedSub.FixedArgTypes;
-
-            Type[] output = new Type[Params.Count + fixedArgs.Length];
-
-            fixedArgs.CopyTo(output, 0);
+            subroutine.PrepareMethod();
 
-            int typeIdx = fixedArgs.Length;
-
-            for (int index = 0; index < Params.Count; index++)
-            {
-                output[typeIdx++] = GetFieldType(Params[index].Type);
-            }
-
-            return output;
+            return subroutine;
         }
 
         public int GetLocalIndex(Register reg)
diff --git a/ChocolArm64/Translation/ILOpCodeCall.cs b/ChocolArm64/Translation/ILOpCodeCall.cs
index 8486a791..c046aeeb 100644
--- a/ChocolArm64/Translation/ILOpCodeCall.cs
+++ b/ChocolArm64/Translation/ILOpCodeCall.cs
@@ -5,16 +5,19 @@ namespace ChocolArm64.Translation
 {
     struct ILOpCodeCall : IILEmit
     {
-        private MethodInfo _mthdInfo;
+        public MethodInfo Info { get; private set; }
 
-        public ILOpCodeCall(MethodInfo mthdInfo)
+        public bool IsVirtual { get; private set; }
+
+        public ILOpCodeCall(MethodInfo info, bool isVirtual)
         {
-            _mthdInfo = mthdInfo;
+            Info      = info;
+            IsVirtual = isVirtual;
         }
 
         public void Emit(ILMethodBuilder context)
         {
-            context.Generator.Emit(OpCodes.Call, _mthdInfo);
+            context.Generator.Emit(IsVirtual ? OpCodes.Callvirt : OpCodes.Call, Info);
         }
     }
 }
\ No newline at end of file
diff --git a/ChocolArm64/Translation/ILOpCodeLoadField.cs b/ChocolArm64/Translation/ILOpCodeLoadField.cs
new file mode 100644
index 00000000..abcd37c3
--- /dev/null
+++ b/ChocolArm64/Translation/ILOpCodeLoadField.cs
@@ -0,0 +1,20 @@
+using System.Reflection;
+using System.Reflection.Emit;
+
+namespace ChocolArm64.Translation
+{
+    struct ILOpCodeLoadField : IILEmit
+    {
+        public FieldInfo Info { get; private set; }
+
+        public ILOpCodeLoadField(FieldInfo info)
+        {
+            Info = info;
+        }
+
+        public void Emit(ILMethodBuilder context)
+        {
+            context.Generator.Emit(OpCodes.Ldfld, Info);
+        }
+    }
+}
\ No newline at end of file
diff --git a/ChocolArm64/Translation/TranslatedSub.cs b/ChocolArm64/Translation/TranslatedSub.cs
new file mode 100644
index 00000000..65d70351
--- /dev/null
+++ b/ChocolArm64/Translation/TranslatedSub.cs
@@ -0,0 +1,65 @@
+using ChocolArm64.Memory;
+using ChocolArm64.State;
+using System;
+using System.Reflection;
+using System.Reflection.Emit;
+
+namespace ChocolArm64.Translation
+{
+    delegate long ArmSubroutine(CpuThreadState state, MemoryManager memory);
+
+    class TranslatedSub
+    {
+        public ArmSubroutine Delegate { get; private set; }
+
+        public static int StateArgIdx  { get; private set; }
+        public static int MemoryArgIdx { get; private set; }
+
+        public static Type[] FixedArgTypes { get; private set; }
+
+        public DynamicMethod Method { get; private set; }
+
+        public TranslationTier Tier { get; private set; }
+
+        public TranslatedSub(DynamicMethod method, TranslationTier tier)
+        {
+            Method = method ?? throw new ArgumentNullException(nameof(method));;
+            Tier   = tier;
+        }
+
+        static TranslatedSub()
+        {
+            MethodInfo mthdInfo = typeof(ArmSubroutine).GetMethod("Invoke");
+
+            ParameterInfo[] Params = mthdInfo.GetParameters();
+
+            FixedArgTypes = new Type[Params.Length];
+
+            for (int index = 0; index < Params.Length; index++)
+            {
+                Type argType = Params[index].ParameterType;
+
+                FixedArgTypes[index] = argType;
+
+                if (argType == typeof(CpuThreadState))
+                {
+                    StateArgIdx = index;
+                }
+                else if (argType == typeof(MemoryManager))
+                {
+                    MemoryArgIdx = index;
+                }
+            }
+        }
+
+        public void PrepareMethod()
+        {
+            Delegate = (ArmSubroutine)Method.CreateDelegate(typeof(ArmSubroutine));
+        }
+
+        public long Execute(CpuThreadState threadState, MemoryManager memory)
+        {
+            return Delegate(threadState, memory);
+        }
+    }
+}
\ No newline at end of file
diff --git a/ChocolArm64/Translation/TranslationTier.cs b/ChocolArm64/Translation/TranslationTier.cs
new file mode 100644
index 00000000..13afd9c5
--- /dev/null
+++ b/ChocolArm64/Translation/TranslationTier.cs
@@ -0,0 +1,11 @@
+namespace ChocolArm64.Translation
+{
+    enum TranslationTier
+    {
+        Tier0,
+        Tier1,
+        Tier2,
+
+        Count
+    }
+}
\ No newline at end of file
diff --git a/ChocolArm64/Translation/Translator.cs b/ChocolArm64/Translation/Translator.cs
new file mode 100644
index 00000000..7f7df6e5
--- /dev/null
+++ b/ChocolArm64/Translation/Translator.cs
@@ -0,0 +1,188 @@
+using ChocolArm64.Decoders;
+using ChocolArm64.Events;
+using ChocolArm64.Memory;
+using ChocolArm64.State;
+using System;
+using System.Threading;
+
+namespace ChocolArm64.Translation
+{
+    public class Translator
+    {
+        private MemoryManager _memory;
+
+        private CpuThreadState _dummyThreadState;
+
+        private TranslatorCache _cache;
+        private TranslatorQueue _queue;
+
+        private Thread _backgroundTranslator;
+
+        public event EventHandler<CpuTraceEventArgs> CpuTrace;
+
+        public bool EnableCpuTrace { get; set; }
+
+        private volatile int _threadCount;
+
+        public Translator(MemoryManager memory)
+        {
+            _memory = memory;
+
+            _dummyThreadState = new CpuThreadState();
+
+            _dummyThreadState.Running = false;
+
+            _cache = new TranslatorCache();
+            _queue = new TranslatorQueue();
+        }
+
+        internal void ExecuteSubroutine(CpuThread thread, long position)
+        {
+            if (Interlocked.Increment(ref _threadCount) == 1)
+            {
+                _backgroundTranslator = new Thread(TranslateQueuedSubs);
+                _backgroundTranslator.Start();
+            }
+
+            ExecuteSubroutine(thread.ThreadState, position);
+
+            if (Interlocked.Decrement(ref _threadCount) == 0)
+            {
+                _queue.ForceSignal();
+            }
+        }
+
+        private void ExecuteSubroutine(CpuThreadState state, long position)
+        {
+            state.CurrentTranslator = this;
+
+            do
+            {
+                if (EnableCpuTrace)
+                {
+                    CpuTrace?.Invoke(this, new CpuTraceEventArgs(position));
+                }
+
+                TranslatedSub subroutine = GetOrTranslateSubroutine(state, position);
+
+                position = subroutine.Execute(state, _memory);
+            }
+            while (position != 0 && state.Running);
+
+            state.CurrentTranslator = null;
+        }
+
+        internal void TranslateVirtualSubroutine(CpuThreadState state, long position)
+        {
+            if (!_cache.TryGetSubroutine(position, out TranslatedSub sub) || sub.Tier == TranslationTier.Tier0)
+            {
+                _queue.Enqueue(new TranslatorQueueItem(position, state.GetExecutionMode(), TranslationTier.Tier1));
+            }
+        }
+
+        internal ArmSubroutine GetOrTranslateVirtualSubroutine(CpuThreadState state, long position)
+        {
+            if (!_cache.TryGetSubroutine(position, out TranslatedSub sub))
+            {
+                sub = TranslateLowCq(position, state.GetExecutionMode());
+            }
+
+            if (sub.Tier == TranslationTier.Tier0)
+            {
+                _queue.Enqueue(new TranslatorQueueItem(position, state.GetExecutionMode(), TranslationTier.Tier1));
+            }
+
+            return sub.Delegate;
+        }
+
+        internal TranslatedSub GetOrTranslateSubroutine(CpuThreadState state, long position)
+        {
+            if (!_cache.TryGetSubroutine(position, out TranslatedSub subroutine))
+            {
+                subroutine = TranslateLowCq(position, state.GetExecutionMode());
+            }
+
+            return subroutine;
+        }
+
+        private void TranslateQueuedSubs()
+        {
+            while (_threadCount != 0)
+            {
+                if (_queue.TryDequeue(out TranslatorQueueItem item))
+                {
+                    bool isCached = _cache.TryGetSubroutine(item.Position, out TranslatedSub sub);
+
+                    if (isCached && item.Tier <= sub.Tier)
+                    {
+                        continue;
+                    }
+
+                    if (item.Tier == TranslationTier.Tier0)
+                    {
+                        TranslateLowCq(item.Position, item.Mode);
+                    }
+                    else
+                    {
+                        TranslateHighCq(item.Position, item.Mode);
+                    }
+                }
+                else
+                {
+                    _queue.WaitForItems();
+                }
+            }
+        }
+
+        private TranslatedSub TranslateLowCq(long position, ExecutionMode mode)
+        {
+            Block block = Decoder.DecodeBasicBlock(_memory, position, mode);
+
+            ILEmitterCtx context = new ILEmitterCtx(_cache, _queue, TranslationTier.Tier0, block);
+
+            string subName = GetSubroutineName(position);
+
+            ILMethodBuilder ilMthdBuilder = new ILMethodBuilder(context.GetILBlocks(), subName);
+
+            TranslatedSub subroutine = ilMthdBuilder.GetSubroutine(TranslationTier.Tier0);
+
+            return _cache.GetOrAdd(position, subroutine, block.OpCodes.Count);
+        }
+
+        private void TranslateHighCq(long position, ExecutionMode mode)
+        {
+            Block graph = Decoder.DecodeSubroutine(_memory, position, mode);
+
+            ILEmitterCtx context = new ILEmitterCtx(_cache, _queue, TranslationTier.Tier1, graph);
+
+            ILBlock[] ilBlocks = context.GetILBlocks();
+
+            string subName = GetSubroutineName(position);
+
+            ILMethodBuilder ilMthdBuilder = new ILMethodBuilder(ilBlocks, subName);
+
+            TranslatedSub subroutine = ilMthdBuilder.GetSubroutine(TranslationTier.Tier1);
+
+            int ilOpCount = 0;
+
+            foreach (ILBlock ilBlock in ilBlocks)
+            {
+                ilOpCount += ilBlock.Count;
+            }
+
+            _cache.AddOrUpdate(position, subroutine, ilOpCount);
+
+            ForceAheadOfTimeCompilation(subroutine);
+        }
+
+        private string GetSubroutineName(long position)
+        {
+            return $"Sub{position:x16}";
+        }
+
+        private void ForceAheadOfTimeCompilation(TranslatedSub subroutine)
+        {
+            subroutine.Execute(_dummyThreadState, null);
+        }
+    }
+}
\ No newline at end of file
diff --git a/ChocolArm64/Translation/TranslatorCache.cs b/ChocolArm64/Translation/TranslatorCache.cs
new file mode 100644
index 00000000..d10d6757
--- /dev/null
+++ b/ChocolArm64/Translation/TranslatorCache.cs
@@ -0,0 +1,196 @@
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Runtime.CompilerServices;
+using System.Threading;
+
+namespace ChocolArm64.Translation
+{
+    class TranslatorCache
+    {
+        //Maximum size of the cache, the unit used is completely arbitrary.
+        private const int MaxTotalSize = 0x800000;
+
+        //Minimum time required in milliseconds for a method to be eligible for deletion.
+        private const int MinTimeDelta = 2 * 60000;
+
+        //Minimum number of calls required to update the timestamp.
+        private const int MinCallCountForUpdate = 250;
+
+        private class CacheBucket
+        {
+            public TranslatedSub Subroutine { get; private set; }
+
+            public LinkedListNode<long> Node { get; private set; }
+
+            public int CallCount { get; set; }
+
+            public int Size { get; private set; }
+
+            public long Timestamp { get; private set; }
+
+            public CacheBucket(TranslatedSub subroutine, LinkedListNode<long> node, int size)
+            {
+                Subroutine = subroutine;
+                Size       = size;
+
+                UpdateNode(node);
+            }
+
+            public void UpdateNode(LinkedListNode<long> node)
+            {
+                Node = node;
+
+                Timestamp = GetTimestamp();
+            }
+        }
+
+        private ConcurrentDictionary<long, CacheBucket> _cache;
+
+        private LinkedList<long> _sortedCache;
+
+        private int _totalSize;
+
+        public TranslatorCache()
+        {
+            _cache = new ConcurrentDictionary<long, CacheBucket>();
+
+            _sortedCache = new LinkedList<long>();
+        }
+
+        public TranslatedSub GetOrAdd(long position, TranslatedSub subroutine, int size)
+        {
+            ClearCacheIfNeeded();
+
+            lock (_sortedCache)
+            {
+                LinkedListNode<long> node = _sortedCache.AddLast(position);
+
+                CacheBucket bucket = new CacheBucket(subroutine, node, size);
+
+                bucket = _cache.GetOrAdd(position, bucket);
+
+                if (bucket.Node == node)
+                {
+                    _totalSize += size;
+                }
+                else
+                {
+                    _sortedCache.Remove(node);
+                }
+
+                return bucket.Subroutine;
+            }
+        }
+
+        public void AddOrUpdate(long position, TranslatedSub subroutine, int size)
+        {
+            ClearCacheIfNeeded();
+
+            lock (_sortedCache)
+            {
+                _totalSize += size;
+
+                LinkedListNode<long> node = _sortedCache.AddLast(position);
+
+                CacheBucket newBucket = new CacheBucket(subroutine, node, size);
+
+                _cache.AddOrUpdate(position, newBucket, (key, bucket) =>
+                {
+                    _totalSize -= bucket.Size;
+
+                    _sortedCache.Remove(bucket.Node);
+
+                    return newBucket;
+                });
+            }
+        }
+
+        public bool HasSubroutine(long position)
+        {
+            return _cache.ContainsKey(position);
+        }
+
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        public bool TryGetSubroutine(long position, out TranslatedSub subroutine)
+        {
+            if (_cache.TryGetValue(position, out CacheBucket bucket))
+            {
+                if (bucket.CallCount++ > MinCallCountForUpdate)
+                {
+                    if (Monitor.TryEnter(_sortedCache))
+                    {
+                        try
+                        {
+                            //The bucket value on the dictionary may have changed between the
+                            //time we get the value from the dictionary, and we acquire the
+                            //lock. So we need to ensure we are working with the latest value,
+                            //we can do that by getting the value again, inside the lock.
+                            if (_cache.TryGetValue(position, out CacheBucket latestBucket))
+                            {
+                                latestBucket.CallCount = 0;
+
+                                _sortedCache.Remove(latestBucket.Node);
+
+                                latestBucket.UpdateNode(_sortedCache.AddLast(position));
+                            }
+                        }
+                        finally
+                        {
+                            Monitor.Exit(_sortedCache);
+                        }
+                    }
+                }
+
+                subroutine = bucket.Subroutine;
+
+                return true;
+            }
+
+            subroutine = default(TranslatedSub);
+
+            return false;
+        }
+
+        private void ClearCacheIfNeeded()
+        {
+            long timestamp = GetTimestamp();
+
+            while (_totalSize > MaxTotalSize)
+            {
+                lock (_sortedCache)
+                {
+                    LinkedListNode<long> node = _sortedCache.First;
+
+                    if (node == null)
+                    {
+                        break;
+                    }
+
+                    CacheBucket bucket = _cache[node.Value];
+
+                    long timeDelta = timestamp - bucket.Timestamp;
+
+                    if (timeDelta <= MinTimeDelta)
+                    {
+                        break;
+                    }
+
+                    if (_cache.TryRemove(node.Value, out bucket))
+                    {
+                        _totalSize -= bucket.Size;
+
+                        _sortedCache.Remove(bucket.Node);
+                    }
+                }
+            }
+        }
+
+        private static long GetTimestamp()
+        {
+            long timestamp = Stopwatch.GetTimestamp();
+
+            return timestamp / (Stopwatch.Frequency / 1000);
+        }
+    }
+}
\ No newline at end of file
diff --git a/ChocolArm64/Translation/TranslatorQueue.cs b/ChocolArm64/Translation/TranslatorQueue.cs
new file mode 100644
index 00000000..89d665bf
--- /dev/null
+++ b/ChocolArm64/Translation/TranslatorQueue.cs
@@ -0,0 +1,83 @@
+using System.Collections.Concurrent;
+using System.Threading;
+
+namespace ChocolArm64.Translation
+{
+    class TranslatorQueue
+    {
+        //This is the maximum number of functions to be translated that the queue can hold.
+        //The value may need some tuning to find the sweet spot.
+        private const int MaxQueueSize = 1024;
+
+        private ConcurrentStack<TranslatorQueueItem>[] _translationQueue;
+
+        private ManualResetEvent _queueDataReceivedEvent;
+
+        private bool _signaled;
+
+        public TranslatorQueue()
+        {
+            _translationQueue = new ConcurrentStack<TranslatorQueueItem>[(int)TranslationTier.Count];
+
+            for (int prio = 0; prio < _translationQueue.Length; prio++)
+            {
+                _translationQueue[prio] = new ConcurrentStack<TranslatorQueueItem>();
+            }
+
+            _queueDataReceivedEvent = new ManualResetEvent(false);
+        }
+
+        public void Enqueue(TranslatorQueueItem item)
+        {
+            ConcurrentStack<TranslatorQueueItem> queue = _translationQueue[(int)item.Tier];
+
+            if (queue.Count >= MaxQueueSize)
+            {
+                queue.TryPop(out _);
+            }
+
+            queue.Push(item);
+
+            _queueDataReceivedEvent.Set();
+        }
+
+        public bool TryDequeue(out TranslatorQueueItem item)
+        {
+            for (int prio = 0; prio < _translationQueue.Length; prio++)
+            {
+                if (_translationQueue[prio].TryPop(out item))
+                {
+                    return true;
+                }
+            }
+
+            item = default(TranslatorQueueItem);
+
+            return false;
+        }
+
+        public void WaitForItems()
+        {
+            _queueDataReceivedEvent.WaitOne();
+
+            lock (_queueDataReceivedEvent)
+            {
+                if (!_signaled)
+                {
+                    _queueDataReceivedEvent.Reset();
+                }
+            }
+        }
+
+        public void ForceSignal()
+        {
+            lock (_queueDataReceivedEvent)
+            {
+                _signaled = true;
+
+                _queueDataReceivedEvent.Set();
+                _queueDataReceivedEvent.Close();
+            }
+        }
+    }
+}
\ No newline at end of file
diff --git a/ChocolArm64/Translation/TranslatorQueueItem.cs b/ChocolArm64/Translation/TranslatorQueueItem.cs
new file mode 100644
index 00000000..0988414a
--- /dev/null
+++ b/ChocolArm64/Translation/TranslatorQueueItem.cs
@@ -0,0 +1,20 @@
+using ChocolArm64.State;
+
+namespace ChocolArm64.Translation
+{
+    struct TranslatorQueueItem
+    {
+        public long Position { get; }
+
+        public ExecutionMode Mode { get; }
+
+        public TranslationTier Tier { get; }
+
+        public TranslatorQueueItem(long position, ExecutionMode mode, TranslationTier tier)
+        {
+            Position = position;
+            Mode     = mode;
+            Tier     = tier;
+        }
+    }
+}
\ No newline at end of file