potential fix for locking issues

tanks-backend/TanksServer/Endpoints.cs

@@ -80,8 +80,6 @@ internal sealed class Endpoints(
         if (name.Length > 12) return TypedResults.BadRequest("name too long");
 
         var player = playerService.GetOrAdd(name);
-        return player != null
+        return TypedResults.Ok(player.Name);
-            ? TypedResults.Ok(player.Name)
-            : TypedResults.Unauthorized();
     }
 }

tanks-backend/TanksServer/GameLogic/CollectPowerUp.cs

@@ -4,10 +4,10 @@ internal sealed class CollectPowerUp(
     MapEntityManager entityManager
 ) : ITickStep
 {
-    public Task TickAsync(TimeSpan delta)
+    public ValueTask TickAsync(TimeSpan delta)
     {
         entityManager.RemoveWhere(TryCollect);
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 
     private bool TryCollect(PowerUp obj)

tanks-backend/TanksServer/GameLogic/CollideBullets.cs

@@ -9,12 +9,12 @@ internal sealed class CollideBullets(
 {
     private const int ExplosionRadius = 3;
 
-    public Task TickAsync(TimeSpan _)
+    public ValueTask TickAsync(TimeSpan _)
     {
         entityManager.RemoveWhere(BulletHitsTank);
         entityManager.RemoveWhere(BulletHitsWall);
         entityManager.RemoveWhere(BulletTimesOut);
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 
     private bool BulletTimesOut(Bullet bullet)

tanks-backend/TanksServer/GameLogic/ITickStep.cs

@@ -2,5 +2,5 @@ namespace TanksServer.GameLogic;
 
 public interface ITickStep
 {
-    Task TickAsync(TimeSpan delta);
+    ValueTask TickAsync(TimeSpan delta);
 }

tanks-backend/TanksServer/GameLogic/MoveBullets.cs

@@ -5,12 +5,12 @@ internal sealed class MoveBullets(
     IOptions<GameRules> config
 ) : ITickStep
 {
-    public Task TickAsync(TimeSpan delta)
+    public ValueTask TickAsync(TimeSpan delta)
     {
         foreach (var bullet in entityManager.Bullets)
             MoveBullet(bullet, delta);
 
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 
     private void MoveBullet(Bullet bullet, TimeSpan delta)

tanks-backend/TanksServer/GameLogic/MoveTanks.cs

@@ -8,12 +8,12 @@ internal sealed class MoveTanks(
 {
     private readonly GameRules _config = options.Value;
 
-    public Task TickAsync(TimeSpan delta)
+    public ValueTask TickAsync(TimeSpan delta)
     {
         foreach (var tank in entityManager.Tanks)
             tank.Moving = TryMoveTank(tank, delta);
 
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 
     private bool TryMoveTank(Tank tank, TimeSpan delta)

tanks-backend/TanksServer/GameLogic/RotateTanks.cs

@@ -8,7 +8,7 @@ internal sealed class RotateTanks(
 {
     private readonly GameRules _config = options.Value;
 
-    public Task TickAsync(TimeSpan delta)
+    public ValueTask TickAsync(TimeSpan delta)
     {
         foreach (var tank in entityManager.Tanks)
         {
@@ -30,6 +30,6 @@ internal sealed class RotateTanks(
             logger.LogTrace("rotated tank to {}", tank.Rotation);
         }
 
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 }

tanks-backend/TanksServer/GameLogic/ShootFromTanks.cs

@@ -9,12 +9,12 @@ internal sealed class ShootFromTanks(
 {
     private readonly GameRules _config = options.Value;
 
-    public Task TickAsync(TimeSpan _)
+    public ValueTask TickAsync(TimeSpan _)
     {
         foreach (var tank in entityManager.Tanks.Where(t => !t.Moving))
             Shoot(tank);
 
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 
     private void Shoot(Tank tank)

tanks-backend/TanksServer/GameLogic/SpawnPowerUp.cs

@@ -8,14 +8,14 @@ internal sealed class SpawnPowerUp(
     private readonly double _spawnChance = options.Value.PowerUpSpawnChance;
     private readonly int _maxCount = options.Value.MaxPowerUpCount;
 
-    public Task TickAsync(TimeSpan delta)
+    public ValueTask TickAsync(TimeSpan delta)
     {
         if (entityManager.PowerUps.Count() >= _maxCount)
-            return Task.CompletedTask;
+            return ValueTask.CompletedTask;
         if (Random.Shared.NextDouble() > _spawnChance * delta.TotalSeconds)
-            return Task.CompletedTask;
+            return ValueTask.CompletedTask;
 
         entityManager.SpawnPowerUp();
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 }

tanks-backend/TanksServer/GameLogic/TankSpawnQueue.cs

@@ -43,12 +43,12 @@ internal sealed class TankSpawnQueue(
         return true;
     }
 
-    public Task TickAsync(TimeSpan _)
+    public ValueTask TickAsync(TimeSpan _)
     {
         if (!TryDequeueNext(out var player))
-            return Task.CompletedTask;
+            return ValueTask.CompletedTask;
 
         entityManager.SpawnTank(player);
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }
 }

tanks-backend/TanksServer/Graphics/GeneratePixelsTickStep.cs

@@ -12,7 +12,7 @@ internal sealed class GeneratePixelsTickStep(
     private readonly List<IDrawStep> _drawSteps = drawSteps.ToList();
     private readonly List<IFrameConsumer> _consumers = consumers.ToList();
 
-    public async Task TickAsync(TimeSpan _)
+    public async ValueTask TickAsync(TimeSpan _)
     {
         PixelGrid observerPixelGrid = new(MapService.PixelsPerRow, MapService.PixelsPerColumn);
 

tanks-backend/TanksServer/Graphics/IFrameConsumer.cs

@@ -4,5 +4,5 @@ namespace TanksServer.Graphics;
 
 internal interface IFrameConsumer
 {
-    Task OnFrameDoneAsync(GamePixelGrid gamePixelGrid, PixelGrid observerPixels);
+    ValueTask OnFrameDoneAsync(GamePixelGrid gamePixelGrid, PixelGrid observerPixels);
 }

tanks-backend/TanksServer/Interactivity/ClientScreenServer.cs

@@ -16,6 +16,6 @@ internal sealed class ClientScreenServer(
             player
         ));
 
-    public Task OnFrameDoneAsync(GamePixelGrid gamePixelGrid, PixelGrid observerPixels)
+    public ValueTask OnFrameDoneAsync(GamePixelGrid gamePixelGrid, PixelGrid observerPixels)
         => ParallelForEachConnectionAsync(c => c.OnGameTickAsync(observerPixels, gamePixelGrid).AsTask());
 }

tanks-backend/TanksServer/Interactivity/ClientScreenServerConnection.cs

@@ -8,45 +8,26 @@ internal sealed class ClientScreenServerConnection(
     WebSocket webSocket,
     ILogger<ClientScreenServerConnection> logger,
     string? playerName = null
-) : WebsocketServerConnection(logger, new ByteChannelWebSocket(webSocket, logger, 0)),
+) : WebsocketServerConnection(logger, new ByteChannelWebSocket(webSocket, logger, 0))
-    IDisposable
 {
-    private readonly SemaphoreSlim _wantedFramesOnTick = new(0, 2);
+    private bool _wantsFrameOnTick = true;
-    private readonly SemaphoreSlim _mutex = new(1);
 
-    private PixelGrid? _lastSentPixels = null;
+    private PixelGrid? _lastSentPixels;
-    private PixelGrid? _nextPixels = null;
+    private PixelGrid? _nextPixels;
     private readonly PlayerScreenData? _nextPlayerData = playerName != null ? new PlayerScreenData(logger) : null;
 
-    protected override async ValueTask HandleMessageAsync(Memory<byte> _)
+    protected override async ValueTask HandleMessageLockedAsync(Memory<byte> _)
-    {
-        await _mutex.WaitAsync();
-        try
     {
         if (_nextPixels == null)
         {
-                _wantedFramesOnTick.Release();
+            _wantsFrameOnTick = true;
             return;
         }
 
-            _lastSentPixels = _nextPixels;
+        await SendNowAsync();
-            _nextPixels = null;
-            await SendNowAsync(_lastSentPixels);
-        }
-        catch (SemaphoreFullException)
-        {
-            logger.LogWarning("ignoring request for more frames");
-        }
-        finally
-        {
-            _mutex.Release();
-        }
     }
 
-    public async ValueTask OnGameTickAsync(PixelGrid pixels, GamePixelGrid gamePixelGrid)
+    public ValueTask OnGameTickAsync(PixelGrid pixels, GamePixelGrid gamePixelGrid) => LockedAsync(async () =>
-    {
-        await _mutex.WaitAsync();
-        try
     {
         if (pixels == _lastSentPixels)
             return;
@@ -62,39 +43,31 @@ internal sealed class ClientScreenServerConnection(
             }
         }
 
-            var sendImmediately = await _wantedFramesOnTick.WaitAsync(TimeSpan.Zero);
-            if (sendImmediately)
-            {
-                await SendNowAsync(pixels);
-                return;
-            }
-
-            _wantedFramesOnTick.Release();
         _nextPixels = pixels;
-        }
+        if (_wantsFrameOnTick)
-        finally
+            _ = await SendNowAsync();
-        {
+    });
-            _mutex.Release();
-        }
-    }
 
-    private async ValueTask SendNowAsync(PixelGrid pixels)
+    private async ValueTask<bool> SendNowAsync()
     {
-        Logger.LogTrace("sending");
+        var pixels = _nextPixels
+                     ?? throw new InvalidOperationException("next pixels not set");
+
         try
         {
-            Logger.LogTrace("sending {} bytes of pixel data", pixels.Data.Length);
             await Socket.SendBinaryAsync(pixels.Data, _nextPlayerData == null);
             if (_nextPlayerData != null)
-            {
                 await Socket.SendBinaryAsync(_nextPlayerData.GetPacket());
-            }
+
+            _lastSentPixels = _nextPixels;
+            _nextPixels = null;
+            _wantsFrameOnTick = false;
+            return true;
         }
         catch (WebSocketException ex)
         {
             Logger.LogWarning(ex, "send failed");
+            return false;
         }
     }
-
-    public void Dispose() => _wantedFramesOnTick.Dispose();
 }

tanks-backend/TanksServer/Interactivity/ControlsServerConnection.cs

@@ -23,7 +23,7 @@ internal sealed class ControlsServerConnection(
         Shoot = 0x05
     }
 
-    protected override ValueTask HandleMessageAsync(Memory<byte> buffer)
+    protected override ValueTask HandleMessageLockedAsync(Memory<byte> buffer)
     {
         var type = (MessageType)buffer.Span[0];
         var control = (InputType)buffer.Span[1];

tanks-backend/TanksServer/Interactivity/PlayerInfoConnection.cs

@@ -10,19 +10,19 @@ internal sealed class PlayerInfoConnection(
     ILogger logger,
     WebSocket rawSocket,
     MapEntityManager entityManager
-) : WebsocketServerConnection(logger, new ByteChannelWebSocket(rawSocket, logger, 0)), IDisposable
+) : WebsocketServerConnection(logger, new ByteChannelWebSocket(rawSocket, logger, 0))
 {
-    private readonly SemaphoreSlim _wantedFrames = new(1);
     private readonly AppSerializerContext _context = new(new JsonSerializerOptions(JsonSerializerDefaults.Web));
+    private bool _wantsInfoOnTick;
     private byte[] _lastMessage = [];
 
-    protected override ValueTask HandleMessageAsync(Memory<byte> buffer)
+    protected override ValueTask HandleMessageLockedAsync(Memory<byte> buffer)
     {
         var response = GetMessageToSend();
         if (response == null)
         {
             Logger.LogTrace("cannot respond directly, increasing wanted frames");
-            _wantedFrames.Release();
+            _wantsInfoOnTick = true;
             return ValueTask.CompletedTask;
         }
 
@@ -30,21 +30,18 @@ internal sealed class PlayerInfoConnection(
         return Socket.SendTextAsync(response);
     }
 
-    public async Task OnGameTickAsync()
+    public ValueTask OnGameTickAsync() => LockedAsync(() =>
     {
-        if (!await _wantedFrames.WaitAsync(TimeSpan.Zero))
+        if (!_wantsInfoOnTick)
-            return;
+            return ValueTask.CompletedTask;
 
         var response = GetMessageToSend();
         if (response == null)
-        {
+            return ValueTask.CompletedTask;
-            _wantedFrames.Release();
-            return;
-        }
 
         Logger.LogTrace("responding indirectly");
-        await Socket.SendTextAsync(response);
+        return Socket.SendTextAsync(response);
-    }
+    });
 
     private byte[]? GetMessageToSend()
     {
@@ -77,6 +74,4 @@ internal sealed class PlayerInfoConnection(
         str.Append(']');
         return str.ToString();
     }
-
-    public void Dispose() => _wantedFrames.Dispose();
 }

tanks-backend/TanksServer/Interactivity/PlayerServer.cs

@@ -14,7 +14,7 @@ internal sealed class PlayerServer(
     private readonly Dictionary<string, Player> _players = [];
     private readonly SemaphoreSlim _mutex = new(1, 1);
 
-    public Player? GetOrAdd(string name)
+    public Player GetOrAdd(string name)
     {
         _mutex.Wait();
         try
@@ -67,6 +67,6 @@ internal sealed class PlayerServer(
     public Task HandleClientAsync(WebSocket webSocket, Player player)
         => HandleClientAsync(new PlayerInfoConnection(player, connectionLogger, webSocket, entityManager));
 
-    public Task TickAsync(TimeSpan delta)
+    public ValueTask TickAsync(TimeSpan delta)
-        => ParallelForEachConnectionAsync(connection => connection.OnGameTickAsync());
+        => ParallelForEachConnectionAsync(connection => connection.OnGameTickAsync().AsTask());
 }

tanks-backend/TanksServer/Interactivity/SendToServicePointDisplay.cs

@@ -48,7 +48,7 @@ internal sealed class SendToServicePointDisplay : IFrameConsumer
         };
     }
 
-    public async Task OnFrameDoneAsync(GamePixelGrid gamePixelGrid, PixelGrid observerPixels)
+    public async ValueTask OnFrameDoneAsync(GamePixelGrid gamePixelGrid, PixelGrid observerPixels)
     {
         if (DateTime.Now < _nextFrameAfter)
             return;

tanks-backend/TanksServer/Interactivity/WebsocketServer.cs

@@ -14,7 +14,7 @@ internal abstract class WebsocketServer<T>(
     public async Task StoppingAsync(CancellationToken cancellationToken)
     {
         logger.LogInformation("closing connections");
-        await Locked(async () =>
+        await LockedAsync(async () =>
         {
             _closing = true;
             await Task.WhenAll(_connections.Select(c => c.CloseAsync()));
@@ -22,35 +22,24 @@ internal abstract class WebsocketServer<T>(
         logger.LogInformation("closed connections");
     }
 
-    protected Task ParallelForEachConnectionAsync(Func<T, Task> body)
+    protected ValueTask ParallelForEachConnectionAsync(Func<T, Task> body) =>
-    {
+        LockedAsync(async () => await Task.WhenAll(_connections.Select(body)), CancellationToken.None);
-        _mutex.Wait();
-        try
-        {
-            return Task.WhenAll(_connections.Select(body));
-        }
-        finally
-        {
-            _mutex.Release();
-        }
-    }
 
-    private Task AddConnectionAsync(T connection) => Locked(() =>
+    private ValueTask AddConnectionAsync(T connection) => LockedAsync(async () =>
     {
         if (_closing)
         {
             logger.LogWarning("refusing connection because server is shutting down");
-            return connection.CloseAsync();
+            await connection.CloseAsync();
         }
 
         _connections.Add(connection);
-        return Task.CompletedTask;
     }, CancellationToken.None);
 
-    private Task RemoveConnectionAsync(T connection) => Locked(() =>
+    private ValueTask RemoveConnectionAsync(T connection) => LockedAsync(() =>
     {
         _connections.Remove(connection);
-        return Task.CompletedTask;
+        return ValueTask.CompletedTask;
     }, CancellationToken.None);
 
     protected async Task HandleClientAsync(T connection)
@@ -60,7 +49,7 @@ internal abstract class WebsocketServer<T>(
         await RemoveConnectionAsync(connection);
     }
 
-    private async Task Locked(Func<Task> action, CancellationToken cancellationToken)
+    private async ValueTask LockedAsync(Func<ValueTask> action, CancellationToken cancellationToken)
     {
         await _mutex.WaitAsync(cancellationToken);
         try

tanks-backend/TanksServer/Interactivity/WebsocketServerConnection.cs

@@ -3,8 +3,9 @@ namespace TanksServer.Interactivity;
 internal abstract class WebsocketServerConnection(
     ILogger logger,
     ByteChannelWebSocket socket
-)
+) : IDisposable
 {
+    private readonly SemaphoreSlim _mutex = new(1);
     protected readonly ByteChannelWebSocket Socket = socket;
     protected readonly ILogger Logger = logger;
 
@@ -17,9 +18,24 @@ internal abstract class WebsocketServerConnection(
     public async Task ReceiveAsync()
     {
         await foreach (var buffer in Socket.ReadAllAsync())
-            await HandleMessageAsync(buffer);
+            await LockedAsync(() => HandleMessageLockedAsync(buffer));
         Logger.LogTrace("done receiving");
     }
 
-    protected abstract ValueTask HandleMessageAsync(Memory<byte> buffer);
+    protected abstract ValueTask HandleMessageLockedAsync(Memory<byte> buffer);
+
+    protected async ValueTask LockedAsync(Func<ValueTask> action)
+    {
+        await _mutex.WaitAsync();
+        try
+        {
+            await action();
+        }
+        finally
+        {
+            _mutex.Release();
+        }
+    }
+
+    public void Dispose() => _mutex.Dispose();
 }