From 7165fe6abb147e9d7dadb72a32dc7540497e0e45 Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Fri, 27 Nov 2020 14:23:30 -0500
Subject: [PATCH] Thread safe SKTextBlobBuilder

---
 .../Avalonia.Skia/PlatformRenderInterface.cs    | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs b/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs
index 72700fb8fd..6d0be9f64d 100644
--- a/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs
+++ b/src/Skia/Avalonia.Skia/PlatformRenderInterface.cs
@@ -3,6 +3,8 @@ using System.Collections;
 using System.Collections.Generic;
 using System.IO; 
 using System.Linq;
+using System.Threading;
+
 using Avalonia.Controls.Platform.Surfaces;
 using Avalonia.Media;
 using Avalonia.OpenGL;
@@ -166,12 +168,13 @@ namespace Avalonia.Skia
             LinearMetrics = true
         };
 
-        private static readonly SKTextBlobBuilder s_textBlobBuilder = new SKTextBlobBuilder();
+        private static readonly ThreadLocal<SKTextBlobBuilder> s_textBlobBuilderThreadLocal = new ThreadLocal<SKTextBlobBuilder>(() => new SKTextBlobBuilder());
 
         /// <inheritdoc />
         public IGlyphRunImpl CreateGlyphRun(GlyphRun glyphRun, out double width)
         {
             var count = glyphRun.GlyphIndices.Length;
+            var textBlobBuilder = s_textBlobBuilderThreadLocal.Value;
 
             var glyphTypeface = (GlyphTypefaceImpl)glyphRun.GlyphTypeface.PlatformImpl;
 
@@ -191,15 +194,15 @@ namespace Avalonia.Skia
             {
                 if (glyphTypeface.IsFixedPitch)
                 {
-                    s_textBlobBuilder.AddRun(glyphRun.GlyphIndices.Buffer.Span, s_font);
+                    textBlobBuilder.AddRun(glyphRun.GlyphIndices.Buffer.Span, s_font);
 
-                    textBlob = s_textBlobBuilder.Build();
+                    textBlob = textBlobBuilder.Build();
 
                     width = glyphTypeface.GetGlyphAdvance(glyphRun.GlyphIndices[0]) * scale * glyphRun.GlyphIndices.Length;
                 }
                 else
                 {
-                    var buffer = s_textBlobBuilder.AllocateHorizontalRun(s_font, count, 0);
+                    var buffer = textBlobBuilder.AllocateHorizontalRun(s_font, count, 0);
 
                     var positions = buffer.GetPositionSpan();
 
@@ -219,12 +222,12 @@ namespace Avalonia.Skia
 
                     buffer.SetGlyphs(glyphRun.GlyphIndices.Buffer.Span);
 
-                    textBlob = s_textBlobBuilder.Build();
+                    textBlob = textBlobBuilder.Build();
                 }
             }
             else
             {
-                var buffer = s_textBlobBuilder.AllocatePositionedRun(s_font, count);
+                var buffer = textBlobBuilder.AllocatePositionedRun(s_font, count);
 
                 var glyphPositions = buffer.GetPositionSpan();
 
@@ -250,7 +253,7 @@ namespace Avalonia.Skia
 
                 width = currentX;
 
-                textBlob = s_textBlobBuilder.Build();
+                textBlob = textBlobBuilder.Build();
             }
 
             return new GlyphRunImpl(textBlob);