Add DuplicatePropertyNameChecker to ObjectPool

src/Microsoft.OData.Core/IWriterValidator.cs

@@ -15,10 +15,15 @@ namespace Microsoft.OData
     internal interface IWriterValidator
     {
         /// <summary>
-        /// Creates a DuplicatePropertyNameChecker instance.
+        /// Get a DuplicatePropertyNameChecker instance from the object pool.
         /// </summary>
-        /// <returns>The created instance.</returns>
-        IDuplicatePropertyNameChecker CreateDuplicatePropertyNameChecker();
+        /// <returns>The instance retrieved from the object pool.</returns>
+        IDuplicatePropertyNameChecker GetDuplicatePropertyNameChecker();
+
+        /// <summary>
+        /// Return a DuplicatePropertyNameChecker instance to the object pool.
+        /// </summary>
+        void ReturnDuplicatePropertyNameChecker(IDuplicatePropertyNameChecker duplicatePropertyNameChecker);
 
         /// <summary>
         /// Validates a resource in an expanded link to make sure that the types match.

src/Microsoft.OData.Core/Json/JsonLightInstanceAnnotationWriter.cs

@@ -201,11 +201,13 @@ internal void WriteInstanceAnnotation(
             ODataResourceValue resourceValue = value as ODataResourceValue;
             if (resourceValue != null)
             {
+                IDuplicatePropertyNameChecker duplicatePropertyNameChecker = this.valueSerializer.GetDuplicatePropertyNameChecker();
                 this.WriteInstanceAnnotationName(propertyName, name);
                 this.valueSerializer.WriteResourceValue(resourceValue,
                     expectedType,
                     treatLikeOpenProperty,
-                    this.valueSerializer.CreateDuplicatePropertyNameChecker());
+                    duplicatePropertyNameChecker);
+                this.valueSerializer.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
                 return;
             }
 
@@ -389,12 +391,14 @@ await this.valueSerializer.WriteNullValueAsync()
             ODataResourceValue resourceValue = annotationValue as ODataResourceValue;
             if (resourceValue != null)
             {
+                IDuplicatePropertyNameChecker duplicatePropertyNameChecker = this.valueSerializer.GetDuplicatePropertyNameChecker();
                 await this.WriteInstanceAnnotationNameAsync(propertyName, annotationName)
                     .ConfigureAwait(false);
                 await this.valueSerializer.WriteResourceValueAsync(resourceValue,
                     expectedType,
                     treatLikeOpenProperty,
-                    this.valueSerializer.CreateDuplicatePropertyNameChecker()).ConfigureAwait(false);
+                    duplicatePropertyNameChecker).ConfigureAwait(false);
+                this.valueSerializer.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
                 return;
             }
 

src/Microsoft.OData.Core/JsonLight/ODataJsonLightPropertySerializer.cs

@@ -78,14 +78,17 @@ internal void WriteTopLevelProperty(ODataProperty property)
 
                     // Note we do not allow named stream properties to be written as top level property.
                     this.JsonLightValueSerializer.AssertRecursionDepthIsZero();
+                    IDuplicatePropertyNameChecker duplicatePropertyNameChecker = this.GetDuplicatePropertyNameChecker();
+
                     this.WriteProperty(
                         property,
-                        null /*owningType*/,
-                        true /* isTopLevel */,
-                        this.CreateDuplicatePropertyNameChecker(),
-                        null /* metadataBuilder */);
-                    this.JsonLightValueSerializer.AssertRecursionDepthIsZero();
+                        owningType: null,
+                        isTopLevel: true,
+                        duplicatePropertyNameChecker: duplicatePropertyNameChecker,
+                        metadataBuilder : null);
 
+                    this.JsonLightValueSerializer.AssertRecursionDepthIsZero();
+                    this.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
                     this.JsonWriter.EndObjectScope();
                 });
         }
@@ -276,14 +279,17 @@ await this.WriteContextUriPropertyAsync(kind, () => contextInfo)
 
                     // Note we do not allow named stream properties to be written as top level property.
                     this.JsonLightValueSerializer.AssertRecursionDepthIsZero();
+                    IDuplicatePropertyNameChecker duplicatePropertyNameChecker = this.GetDuplicatePropertyNameChecker();
+
                     await this.WritePropertyAsync(
                         property,
-                        null /*owningType*/,
-                        true /* isTopLevel */,
-                        this.CreateDuplicatePropertyNameChecker(),
-                        null /* metadataBuilder */).ConfigureAwait(false);
-                    this.JsonLightValueSerializer.AssertRecursionDepthIsZero();
+                        owningType : null,
+                        isTopLevel : true,
+                        duplicatePropertyNameChecker : duplicatePropertyNameChecker,
+                        metadataBuilder : null).ConfigureAwait(false);
 
+                    this.JsonLightValueSerializer.AssertRecursionDepthIsZero();
+                    this.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
                     await this.AsynchronousJsonWriter.EndObjectScopeAsync().ConfigureAwait(false);
                 });
         }
@@ -645,11 +651,15 @@ private void WriteResourceProperty(
             Debug.Assert(!this.currentPropertyInfo.IsTopLevel, "Resource property should not be top level");
             this.JsonWriter.WriteName(property.Name);
 
+            IDuplicatePropertyNameChecker duplicatePropertyNameChecker = this.GetDuplicatePropertyNameChecker();
+
             this.JsonLightValueSerializer.WriteResourceValue(
                 resourceValue,
                 this.currentPropertyInfo.MetadataType.TypeReference,
                 isOpenPropertyType,
-                this.CreateDuplicatePropertyNameChecker());
+                duplicatePropertyNameChecker);
+
+            this.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
         }
 
         /// <summary>
@@ -1071,11 +1081,15 @@ private async Task WriteResourcePropertyAsync(
             await this.AsynchronousJsonWriter.WriteNameAsync(property.Name)
                 .ConfigureAwait(false);
 
+            IDuplicatePropertyNameChecker duplicatePropertyNameChecker = this.GetDuplicatePropertyNameChecker();
+
             await this.JsonLightValueSerializer.WriteResourceValueAsync(
                 resourceValue,
                 this.currentPropertyInfo.MetadataType.TypeReference,
                 isOpenPropertyType,
-                this.CreateDuplicatePropertyNameChecker()).ConfigureAwait(false);
+                duplicatePropertyNameChecker).ConfigureAwait(false);
+
+            this.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
         }
 
         /// <summary>

src/Microsoft.OData.Core/JsonLight/ODataJsonLightValueSerializer.cs

@@ -245,7 +245,7 @@ public virtual void WriteCollectionValue(
                     {
                         if (duplicatePropertyNamesChecker == null)
                         {
-                            duplicatePropertyNamesChecker = this.CreateDuplicatePropertyNameChecker();
+                            duplicatePropertyNamesChecker = this.GetDuplicatePropertyNameChecker();
                         }
 
                         this.WriteResourceValue(
@@ -286,6 +286,11 @@ public virtual void WriteCollectionValue(
                         }
                     }
                 }
+
+                if (duplicatePropertyNamesChecker != null)
+                {
+                    this.ReturnDuplicatePropertyNameChecker(duplicatePropertyNamesChecker);
+                }
             }
 
             // End the array scope which holds the items
@@ -567,7 +572,7 @@ await this.AsynchronousODataAnnotationWriter.WriteODataTypeInstanceAnnotationAsy
                     {
                         if (duplicatePropertyNamesChecker == null)
                         {
-                            duplicatePropertyNamesChecker = this.CreateDuplicatePropertyNameChecker();
+                            duplicatePropertyNamesChecker = this.GetDuplicatePropertyNameChecker();
                         }
 
                         await this.WriteResourceValueAsync(
@@ -608,6 +613,11 @@ await this.WriteResourceValueAsync(
                         }
                     }
                 }
+
+                if (duplicatePropertyNamesChecker != null)
+                {
+                    this.ReturnDuplicatePropertyNameChecker(duplicatePropertyNamesChecker);
+                }
             }
 
             // End the array scope which holds the items

src/Microsoft.OData.Core/JsonLight/ODataJsonLightWriter.cs

@@ -487,6 +487,9 @@ protected override void EndResource(ODataResource resource)
 
             this.jsonLightResourceSerializer.WriteResourceEndMetadataProperties(resourceScope, resourceScope.DuplicatePropertyNameChecker);
 
+            // Release the DuplicatePropertyNameChecker to the ObjectPool since an instance is removed from the ObjectPool each time we create a ResourceScope.
+            this.jsonLightResourceSerializer.ReturnDuplicatePropertyNameChecker(resourceScope.DuplicatePropertyNameChecker);
+
             // Close the object scope
             this.jsonWriter.EndObjectScope();
         }

src/Microsoft.OData.Core/ODataCollectionWriterCore.cs

@@ -106,7 +106,7 @@ protected IDuplicatePropertyNameChecker DuplicatePropertyNameChecker
             {
                 return duplicatePropertyNameChecker
                        ?? (duplicatePropertyNameChecker
-                           = outputContext.MessageWriterSettings.Validator.CreateDuplicatePropertyNameChecker());
+                           = outputContext.MessageWriterSettings.Validator.GetDuplicatePropertyNameChecker());
             }
         }
 

src/Microsoft.OData.Core/ODataParameterWriterCore.cs

@@ -84,7 +84,7 @@ protected IDuplicatePropertyNameChecker DuplicatePropertyNameChecker
                 return this.duplicatePropertyNameChecker ??
                        (this.duplicatePropertyNameChecker =
                            outputContext.MessageWriterSettings.Validator
-                           .CreateDuplicatePropertyNameChecker());
+                           .GetDuplicatePropertyNameChecker());
             }
         }
 

src/Microsoft.OData.Core/ODataSerializer.cs

@@ -81,12 +81,20 @@ internal IEdmModel Model
         }
 
         /// <summary>
-        /// Creates a new instance of a duplicate property names checker.
+        /// Get an instance of a duplicate property names checker from the object pool.
         /// </summary>
         /// <returns>The newly created instance of duplicate property names checker.</returns>
-        internal IDuplicatePropertyNameChecker CreateDuplicatePropertyNameChecker()
+        internal IDuplicatePropertyNameChecker GetDuplicatePropertyNameChecker()
         {
-            return MessageWriterSettings.Validator.CreateDuplicatePropertyNameChecker();
+            return MessageWriterSettings.Validator.GetDuplicatePropertyNameChecker();
+        }
+
+        /// <summary>
+        /// Returns an instance of a duplicate property names checker to the object pool.
+        /// </summary>
+        internal void ReturnDuplicatePropertyNameChecker(IDuplicatePropertyNameChecker duplicatePropertyNameChecker)
+        {
+            MessageWriterSettings.Validator.ReturnDuplicatePropertyNameChecker(duplicatePropertyNameChecker);
         }
     }
 }

src/Microsoft.OData.Core/ODataWriterCore.cs

@@ -4133,7 +4133,7 @@ internal ResourceBaseScope(WriterState state, ODataResourceBase resource, ODataR
 
                 if (resource != null)
                 {
-                    duplicatePropertyNameChecker = writerSettings.Validator.CreateDuplicatePropertyNameChecker();
+                    duplicatePropertyNameChecker = writerSettings.Validator.GetDuplicatePropertyNameChecker();
                 }
 
                 this.serializationInfo = serializationInfo;

src/Microsoft.OData.Core/ObjectPool.cs

@@ -0,0 +1,100 @@
+//---------------------------------------------------------------------
+// <copyright file="ObjectPool.cs" company="Microsoft">
+//      Copyright (C) Microsoft Corporation. All rights reserved. See License.txt in the project root for license information.
+// </copyright>
+//---------------------------------------------------------------------
+
+using System;
+
+namespace Microsoft.OData
+{
+    /// <summary>
+    /// Manages a pool of reusable objects. An object retrieved from the pool should be returned when it's no longer being used so that it can be later recycled.
+    /// </summary>
+    /// <typeparam name="T">The type of objects to pool.</typeparam>
+    /// <remarks>This object pool is not thread-safe and not intended to be shared across concurrent requests.
+    /// Consider using the DefaultObjectPool in 8.x once we drop support for netstandard 1.1
+    /// </remarks>
+    internal class ObjectPool<T> where T : class
+    {
+        private readonly Func<T> objectGenerator;
+        private ObjectWrapper[] items;
+        private T firstItem;
+
+        // The pool size is equal to the level of nesting in the response.
+        // 32 is an arbitrary figure. Could be adjusted appropriately.
+        private const int POOL_SIZE = 8;
+
+        /// <summary>
+        /// To initialize the object pool.
+        /// </summary>
+        /// <param name="objectGenerator">Used to create an instance of a <typeparamref name="T"/>.</param>
+        public ObjectPool(Func<T> objectGenerator)
+        {
+            this.objectGenerator = objectGenerator ?? throw new ArgumentNullException(nameof(objectGenerator));
+        }
+
+        /// <summary>
+        /// Gets an object from the pool if one is available, otherwise creates one. The object will need to be returned to the pool when no longer in use.
+        /// </summary>
+        /// <returns>An object of type <typeparamref name="T"/> from the pool.</returns>
+        /// <remarks>It's the responsibility of the caller to clean up the object before using it.</remarks>
+        public T Get()
+        {
+            T item = firstItem;
+
+            if (item != null)
+            {
+                firstItem = default(T);
+                return item;
+            }
+
+            if (items == null)
+            {
+                items = new ObjectWrapper[POOL_SIZE];
+            }
+
+            for (int i = 0; i < items.Length; i++)
+            {
+                item = items[i].Element;
+
+                if (item != null)
+                {
+                    items[i].Element = default(T);
+                    return item;
+                }
+            }
+
+            return objectGenerator();
+        }
+
+        /// <summary>
+        /// Return an object to the pool.
+        /// </summary>
+        /// <param name="obj">The object to return to the pool.</param> 
+        public void Return(T obj)
+        {
+            if (firstItem == null)
+            {
+                firstItem = obj;
+                return;
+            }
+
+            for (int i = 0; i < items.Length; ++i)
+            {
+                if (items[i].Element == null)
+                {
+                    items[i].Element = obj;
+                    break;
+                }
+            }
+        }
+
+        // PERF: the struct wrapper avoids array-covariance-checks from the runtime when assigning to elements of the array.
+        // See comment in this PR https://github.com/dotnet/extensions/pull/314#discussion_r169390645
+        private struct ObjectWrapper
+        {
+            public T Element;
+        }
+    }
+}