By reference string comparison in template cache (#1947)

* By reference string comparison in template cache

* Removed by-value template cache

src/Serilog/Core/Pipeline/ByReferenceStringComparer.cs

@@ -0,0 +1,44 @@
+// Copyright 2013-2015 Serilog Contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+namespace Serilog.Core.Pipeline;
+
+class ByReferenceStringComparer : IEqualityComparer, IEqualityComparer<string>
+{
+    public static readonly ByReferenceStringComparer Instance = new();
+
+    ByReferenceStringComparer()
+    {
+    }
+
+    public new bool Equals(object? x, object? y)
+    {
+        return ReferenceEquals(x, y);
+    }
+
+    public int GetHashCode(object obj)
+    {
+        return RuntimeHelpers.GetHashCode(obj);
+    }
+
+    public bool Equals(string? x, string? y)
+    {
+        return ReferenceEquals(x, y);
+    }
+
+    public int GetHashCode(string obj)
+    {
+        return GetHashCode((object) obj);
+    }
+}

src/Serilog/Core/Pipeline/MessageTemplateCache.cs

@@ -28,7 +28,7 @@ class MessageTemplateCache : IMessageTemplateParser
     // https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2#thread-safety
     //
     // Hence the reason to use Hashtable, otherwise read operation should have been placed into the lock section
-    readonly Hashtable _templates = new();
+    readonly Hashtable _templates = new(ByReferenceStringComparer.Instance);
     const int MaxCacheItems = 1000;
     const int MaxCachedTemplateLength = 1024;
 

test/Serilog.PerformanceTests/Support/ConcurrentDictionaryTemplateCache.cs

@@ -4,7 +4,7 @@ class ConcurrentDictionaryMessageTemplateCache : IMessageTemplateParser
 {
     readonly IMessageTemplateParser _innerParser;
 
-    readonly ConcurrentDictionary<string, MessageTemplate> _templates = new();
+    readonly ConcurrentDictionary<string, MessageTemplate> _templates = new(ByReferenceStringComparer.Instance);
 
     const int MaxCacheItems = 1000;
     const int MaxCachedTemplateLength = 1024;

test/Serilog.PerformanceTests/Support/DictionaryMessageTemplateCache.cs

@@ -5,7 +5,7 @@ class DictionaryMessageTemplateCache : IMessageTemplateParser
     readonly IMessageTemplateParser _innerParser;
     readonly object _templatesLock = new();
 
-    readonly Dictionary<string, MessageTemplate> _templates = new();
+    readonly Dictionary<string, MessageTemplate> _templates = new(ByReferenceStringComparer.Instance);
 
     const int MaxCacheItems = 1000;
     const int MaxCachedTemplateLength = 1024;