Avoid string/StringBuilder/char[] allocation in LogValuesFormatter's …

…ctor (#44746) This is producing thousands of allocations at ASP.NET startup, due to almost 1000 call sites to LoggerMessage.Define.
dotnet · Nov 17, 2020 · 69d6127 · 69d6127
1 parent f6bfec0
commit 69d6127
Show file tree

Hide file tree

Showing 2 changed files with 25 additions and 6 deletions.
diff --git a/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/LogValuesFormatter.cs b/src/libraries/Microsoft.Extensions.Logging.Abstractions/src/LogValuesFormatter.cs
@@ -20,6 +20,10 @@ internal class LogValuesFormatter
         private readonly string _format;
         private readonly List<string> _valueNames = new List<string>();
 
+        // NOTE: If this assembly ever builds for netcoreapp, the below code should change to:
+        // - Be annotated as [SkipLocalsInit] to avoid zero'ing the stackalloc'd char span
+        // - Format _valueNames.Count directly into a span
+
         public LogValuesFormatter(string format)
         {
             if (format == null)
@@ -29,35 +33,42 @@ public LogValuesFormatter(string format)
 
             OriginalFormat = format;
 
-            var sb = new StringBuilder();
+            var vsb = new ValueStringBuilder(stackalloc char[256]);
             int scanIndex = 0;
             int endIndex = format.Length;
 
             while (scanIndex < endIndex)
             {
                 int openBraceIndex = FindBraceIndex(format, '{', scanIndex, endIndex);
+                if (scanIndex == 0 && openBraceIndex == endIndex)
+                {
+                    // No holes found.
+                    _format = format;
+                    return;
+                }
+
                 int closeBraceIndex = FindBraceIndex(format, '}', openBraceIndex, endIndex);
 
                 if (closeBraceIndex == endIndex)
                 {
-                    sb.Append(format, scanIndex, endIndex - scanIndex);
+                    vsb.Append(format.AsSpan(scanIndex, endIndex - scanIndex));
                     scanIndex = endIndex;
                 }
                 else
                 {
                     // Format item syntax : { index[,alignment][ :formatString] }.
                     int formatDelimiterIndex = FindIndexOfAny(format, FormatDelimiters, openBraceIndex, closeBraceIndex);
 
-                    sb.Append(format, scanIndex, openBraceIndex - scanIndex + 1);
-                    sb.Append(_valueNames.Count.ToString(CultureInfo.InvariantCulture));
+                    vsb.Append(format.AsSpan(scanIndex, openBraceIndex - scanIndex + 1));
+                    vsb.Append(_valueNames.Count.ToString());
                     _valueNames.Add(format.Substring(openBraceIndex + 1, formatDelimiterIndex - openBraceIndex - 1));
-                    sb.Append(format, formatDelimiterIndex, closeBraceIndex - formatDelimiterIndex + 1);
+                    vsb.Append(format.AsSpan(formatDelimiterIndex, closeBraceIndex - formatDelimiterIndex + 1));
 
                     scanIndex = closeBraceIndex + 1;
                 }
             }
 
-            _format = sb.ToString();
+            _format = vsb.ToString();
         }
 
         public string OriginalFormat { get; private set; }

diff --git a/...soft.Extensions.Logging.Abstractions/src/Microsoft.Extensions.Logging.Abstractions.csproj b/...soft.Extensions.Logging.Abstractions/src/Microsoft.Extensions.Logging.Abstractions.csproj
@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;net461</TargetFrameworks>
     <EnableDefaultItems>true</EnableDefaultItems>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 
   <ItemGroup>
@@ -12,6 +13,13 @@
              Link="Common\src\Extensions\Logging\NullExternalScopeProvider.cs" />
     <Compile Include="$(CommonPath)Extensions\Logging\NullScope.cs"
              Link="Common\src\Extensions\Logging\NullScope.cs" />
+    <Compile Include="$(CommonPath)System\Text\ValueStringBuilder.cs"
+             Link="Common\System\Text\ValueStringBuilder.cs" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="System.Buffers" Version="$(SystemBuffersVersion)" />
+    <PackageReference Include="System.Memory" Version="$(SystemMemoryVersion)" />
   </ItemGroup>
 
 </Project>