Fix Metal renderer memory leakage on macOS

src/Skia/Avalonia.Skia/Gpu/Metal/AutoReleasePool.cs

@@ -0,0 +1,30 @@
+using System;
+using System.Runtime.InteropServices;
+using System.Threading;
+
+namespace Avalonia.Skia.Metal;
+
+internal sealed partial class AutoReleasePool : IDisposable
+{
+    private IntPtr _pool;
+
+    public AutoReleasePool()
+    {
+        _pool = Push();
+    }
+
+    public void Dispose()
+    {
+        var pool = Interlocked.Exchange(ref _pool, IntPtr.Zero);
+        if (pool != IntPtr.Zero)
+        {
+            Pop(pool);
+        }
+    }
+
+    [LibraryImport("libobjc", EntryPoint = "objc_autoreleasePoolPush")]
+    private static partial IntPtr Push();
+
+    [LibraryImport("libobjc", EntryPoint = "objc_autoreleasePoolPop")]
+    private static partial void Pop(IntPtr pool);
+}

src/Skia/Avalonia.Skia/Gpu/Metal/SkiaMetalGpu.cs

@@ -97,15 +97,33 @@ public void Dispose()
         public ISkiaGpuRenderSession BeginRenderingSession(IRenderTarget.RenderTargetSceneInfo sceneInfo)
         {
             // TODO: use expectedPixelSize
-            var session = (_target ?? throw new ObjectDisposedException(nameof(SkiaMetalRenderTarget))).BeginRendering();
-            var backendTarget = new GRBackendRenderTarget(session.Size.Width, session.Size.Height,
-                new GRMtlTextureInfo(session.Texture));
+            IMetalPlatformSurfaceRenderingSession? session = null;
+            GRBackendRenderTarget? backendTarget = null;
+            SKSurface? surface = null;
+            var success = false;
+            try
+            {
+                session = (_target ?? throw new ObjectDisposedException(nameof(SkiaMetalRenderTarget))).BeginRendering();
+                backendTarget = new GRBackendRenderTarget(session.Size.Width, session.Size.Height,
+                    new GRMtlTextureInfo(session.Texture));
 
-            var surface = SKSurface.Create(_gpu._context!, backendTarget,
-                session.IsYFlipped ? GRSurfaceOrigin.BottomLeft : GRSurfaceOrigin.TopLeft,
-                SKColorType.Bgra8888);
+                surface = SKSurface.Create(_gpu._context!, backendTarget,
+                    session.IsYFlipped ? GRSurfaceOrigin.BottomLeft : GRSurfaceOrigin.TopLeft,
+                    SKColorType.Bgra8888);
 
-            return new SkiaMetalRenderSession(_gpu, surface, session, backendTarget);
+                var result = new SkiaMetalRenderSession(_gpu, surface, session, backendTarget);
+                success = true;
+                return result;
+            }
+            finally
+            {
+                if (!success)
+                {
+                    surface?.Dispose();
+                    backendTarget?.Dispose();
+                    session?.Dispose();
+                }
+            }
         }
 
         public PlatformRenderTargetState State => _target?.State ?? PlatformRenderTargetState.Disposed;
@@ -117,12 +135,14 @@ internal class SkiaMetalRenderSession : ISkiaGpuRenderSession
         private SKSurface? _surface;
         private IMetalPlatformSurfaceRenderingSession? _session;
         private GRBackendRenderTarget? _backendTarget;
+        private readonly AutoReleasePool _autoReleasePool;
 
         public SkiaMetalRenderSession(SkiaMetalGpu gpu,
             SKSurface surface,
             IMetalPlatformSurfaceRenderingSession session,
             GRBackendRenderTarget backendTarget)
         {
+            _autoReleasePool = new AutoReleasePool();
             _gpu = gpu;
             _surface = surface;
             _session = session;
@@ -141,6 +161,8 @@ public void Dispose()
             _session = null;
             _backendTarget?.Dispose();
             _backendTarget = null;
+
+            _autoReleasePool.Dispose();
         }
 
         public GRContext GrContext => _gpu._context!;