Cache the per-property key node when serializing

YamlDotNet/Serialization/ObjectGraphTraversalStrategies/FullObjectGraphTraversalStrategy.cs

@@ -21,6 +21,7 @@
 
 using System;
 using System.Collections;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Text;
 using YamlDotNet.Core;
@@ -41,6 +42,11 @@ public class FullObjectGraphTraversalStrategy : IObjectGraphTraversalStrategy
         private readonly INamingConvention namingConvention;
         private readonly IObjectFactory objectFactory;
 
+        // The key node emitted for a property is fully determined by the property's (immutable) name,
+        // so cache it per descriptor instead of allocating a fresh ObjectDescriptor for every property
+        // of every object during serialization.
+        private readonly ConcurrentDictionary<IPropertyDescriptor, ObjectDescriptor> keyNodeDescriptors = new ConcurrentDictionary<IPropertyDescriptor, ObjectDescriptor>();
+
         public FullObjectGraphTraversalStrategy(ITypeInspector typeDescriptor, ITypeResolver typeResolver, int maxRecursion,
             INamingConvention namingConvention, IObjectFactory objectFactory)
         {
@@ -269,7 +275,8 @@ protected virtual void TraverseProperties<TContext>(IObjectDescriptor value, IOb
                 var propertyValue = propertyDescriptor.Read(source);
                 if (visitor.EnterMapping(propertyDescriptor, propertyValue, context, serializer))
                 {
-                    Traverse(null, propertyDescriptor.Name, new ObjectDescriptor(propertyDescriptor.Name, typeof(string), typeof(string), ScalarStyle.Plain), visitor, context, path, serializer);
+                    var keyNode = keyNodeDescriptors.GetOrAdd(propertyDescriptor, static pd => new ObjectDescriptor(pd.Name, typeof(string), typeof(string), ScalarStyle.Plain));
+                    Traverse(null, propertyDescriptor.Name, keyNode, visitor, context, path, serializer);
                     Traverse(propertyDescriptor, propertyDescriptor.Name, propertyValue, visitor, context, path, serializer);
                 }
             }