🧹 Engine initialization/cleanup refactoring (#1201)

- Move static class initialization from Engine to Searcher (prep for multiple, shorter-lived engines)
- Move forced GC collection from Engine to Searcher (prep for multiple engines)
- Prepare engine to be disposed, aka allowing it to be clear its resources (prep for multiple engines, and potential engine re-allocation)
- Remove Engine `_isNewGameCommandSupported` and `_isNewGameComing`
- Dispose Engine `_searchCancellationTokenSource` and `_absoluteSearchCancellationTokenSource`

src/Lynx/Bench.cs

@@ -129,11 +129,6 @@ public partial class Engine
 
         _engineWriter.TryWrite($"Total time: {Utils.CalculateUCITime(totalSeconds)}");
 
-        // Cleanup game
-        NewGame();
-        _isNewGameComing = false;
-        _isNewGameCommandSupported = false;
-
         return (totalNodes, Utils.CalculateNps(totalNodes, totalSeconds));
     }
 

src/Lynx/Engine.cs

@@ -7,14 +7,16 @@
 
 namespace Lynx;
 
-public sealed partial class Engine
+public sealed partial class Engine : IDisposable
 {
     internal const int DefaultMaxDepth = 5;
 
     private static readonly Logger _logger = LogManager.GetCurrentClassLogger();
     private readonly ChannelWriter<object> _engineWriter;
     private readonly TranspositionTable _tt;
 
+    private bool _disposedValue;
+
     private bool _isSearching;
 
     /// <summary>
@@ -32,11 +34,6 @@ public sealed partial class Engine
     /// </summary>
     private bool _stopRequested;
 
-#pragma warning disable IDE0052, CS0414, S4487 // Remove unread private members
-    private bool _isNewGameCommandSupported;
-    private bool _isNewGameComing;
-#pragma warning restore IDE0052, CS0414 // Remove unread private members
-
     public double AverageDepth { get; private set; }
 
     public Game Game { get; private set; }
@@ -52,7 +49,6 @@ public Engine(ChannelWriter<object> engineWriter, TranspositionTable tt)
     {
         AverageDepth = 0;
         Game = new Game(Constants.InitialPositionFEN);
-        _isNewGameComing = true;
         _searchCancellationTokenSource = new();
         _absoluteSearchCancellationTokenSource = new();
         _engineWriter = engineWriter;
@@ -78,13 +74,8 @@ public Engine(ChannelWriter<object> engineWriter, TranspositionTable tt)
 
         _engineWriter = engineWriter;
 
-        // No need for ResetEngine() call here, WarmupEngine -> Bench -> NewGame() calls it
+        NewGame();
 #endif
-
-#pragma warning disable S1215 // "GC.Collect" should not be called
-        GC.Collect();
-        GC.WaitForPendingFinalizers();
-#pragma warning restore S1215 // "GC.Collect" should not be called
     }
 
 #pragma warning disable S1144 // Unused private types or members should be removed - used in Release mode
@@ -93,8 +84,6 @@ private void WarmupEngine()
         _logger.Info("Warming up engine");
         var sw = Stopwatch.StartNew();
 
-        InitializeStaticClasses();
-
         const string goWarmupCommand = "go depth 10";   // ~300 ms
         var command = new GoCommand(goWarmupCommand);
 
@@ -138,16 +127,9 @@ public void NewGame()
         AverageDepth = 0;
         Game.FreeResources();
         Game = new Game(Constants.InitialPositionFEN);
-        _isNewGameComing = true;
-        _isNewGameCommandSupported = true;
         _stopRequested = false;
 
         ResetEngine();
-
-#pragma warning disable S1215 // "GC.Collect" should not be called
-        GC.Collect();
-        GC.WaitForPendingFinalizers();
-#pragma warning restore S1215 // "GC.Collect" should not be called
     }
 
     [SkipLocalsInit]
@@ -156,7 +138,6 @@ public void AdjustPosition(ReadOnlySpan<char> rawPositionCommand)
         Span<Move> moves = stackalloc Move[Constants.MaxNumberOfPossibleMovesInAPosition];
         Game.FreeResources();
         Game = PositionCommand.ParseGame(rawPositionCommand, moves);
-        _isNewGameComing = false;
         _stopRequested = false;
     }
 
@@ -303,14 +284,32 @@ public void StopSearching()
         _absoluteSearchCancellationTokenSource.Cancel();
     }
 
-    private static void InitializeStaticClasses()
+    public void FreeResources()
+    {
+        Game.FreeResources();
+
+        _absoluteSearchCancellationTokenSource.Dispose();
+        _searchCancellationTokenSource.Dispose();
+
+        _disposedValue = true;
+    }
+
+    private void Dispose(bool disposing)
+    {
+        if (!_disposedValue)
+        {
+            if (disposing)
+            {
+                FreeResources();
+            }
+            _disposedValue = true;
+        }
+    }
+
+    public void Dispose()
     {
-        _ = PVTable.Indexes[0];
-        _ = Attacks.KingAttacks;
-        _ = ZobristTable.SideHash();
-        _ = Masks.FileMasks;
-        _ = EvaluationConstants.HistoryBonus[1];
-        _ = MoveGenerator.Init();
-        _ = GoCommand.Init();
+        // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
+        Dispose(disposing: true);
+        GC.SuppressFinalize(this);
     }
 }

src/Lynx/Searcher.cs

@@ -27,6 +27,8 @@ public Searcher(ChannelReader<string> uciReader, ChannelWriter<object> engineWri
         _engine = new Engine(_engineWriter, _ttWrapper);
 
         _logger = LogManager.GetCurrentClassLogger();
+
+        InitializeStaticClasses();
     }
 
     public async Task Run(CancellationToken cancellationToken)
@@ -97,6 +99,11 @@ public void NewGame()
         }
 
         _engine.NewGame();
+
+#pragma warning disable S1215 // "GC.Collect" should not be called
+        GC.Collect();
+        GC.WaitForPendingFinalizers();
+#pragma warning restore S1215 // "GC.Collect" should not be called
     }
 
     public void Quit()
@@ -113,4 +120,15 @@ public async ValueTask RunBench(int depth)
         var results = _engine.Bench(depth);
         await _engine.PrintBenchResults(results);
     }
+
+    private static void InitializeStaticClasses()
+    {
+        _ = PVTable.Indexes[0];
+        _ = Attacks.KingAttacks;
+        _ = ZobristTable.SideHash();
+        _ = Masks.FileMasks;
+        _ = EvaluationConstants.HistoryBonus[1];
+        _ = MoveGenerator.Init();
+        _ = GoCommand.Init();
+    }
 }