PooledObjectPolicy as abstract base class for avoiding interface call

src/Microsoft.Extensions.ObjectPool/DefaultObjectPool.cs

@@ -15,6 +15,9 @@ public class DefaultObjectPool<T> : ObjectPool<T> where T : class
         private readonly bool _isDefaultPolicy;
         private T _firstItem;
 
+        // This class was introduced in 2.1 to avoid the interface call where possible
+        private readonly PooledObjectPolicy<T> _fastPolicy;
+
         public DefaultObjectPool(IPooledObjectPolicy<T> policy)
             : this(policy, Environment.ProcessorCount * 2)
         {
@@ -23,6 +26,7 @@ public DefaultObjectPool(IPooledObjectPolicy<T> policy)
         public DefaultObjectPool(IPooledObjectPolicy<T> policy, int maximumRetained)
         {
             _policy = policy ?? throw new ArgumentNullException(nameof(policy));
+            _fastPolicy = policy as PooledObjectPolicy<T>;
             _isDefaultPolicy = IsDefaultPolicy();
 
             // -1 due to _firstItem
@@ -64,12 +68,16 @@ private T GetViaScan()
                 }
             }
 
-            return item ?? _policy.Create();
+            return item ?? Create();
         }
 
+        // Non-inline to improve its code quality as uncommon path
+        [MethodImpl(MethodImplOptions.NoInlining)]
+        private T Create() => _fastPolicy?.Create() ?? _policy.Create();
+
         public override void Return(T obj)
         {
-            if (_isDefaultPolicy || _policy.Return(obj))
+            if (_isDefaultPolicy || (_fastPolicy?.Return(obj) ?? _policy.Return(obj)))
             {
                 if (_firstItem != null || Interlocked.CompareExchange(ref _firstItem, obj, null) != null)
                 {

src/Microsoft.Extensions.ObjectPool/DefaultPooledObjectPolicy.cs

@@ -3,16 +3,16 @@
 
 namespace Microsoft.Extensions.ObjectPool
 {
-    public class DefaultPooledObjectPolicy<T> : IPooledObjectPolicy<T> where T : class, new()
+    public class DefaultPooledObjectPolicy<T> : PooledObjectPolicy<T> where T : class, new()
     {
-        public T Create()
+        public override T Create()
         {
             return new T();
         }
 
         // DefaultObjectPool<T> doesn't call 'Return' for the default policy.
         // So take care adding any logic to this method, as it might require changes elsewhere.
-        public bool Return(T obj)
+        public override bool Return(T obj)
         {
             return true;
         }

src/Microsoft.Extensions.ObjectPool/PooledObjectPolicy.cs

@@ -0,0 +1,12 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.Extensions.ObjectPool
+{
+    public abstract class PooledObjectPolicy<T> : IPooledObjectPolicy<T>
+    {
+        public abstract T Create();
+
+        public abstract bool Return(T obj);
+    }
+}

src/Microsoft.Extensions.ObjectPool/StringBuilderPooledObjectPolicy.cs

@@ -5,18 +5,18 @@
 
 namespace Microsoft.Extensions.ObjectPool
 {
-    public class StringBuilderPooledObjectPolicy : IPooledObjectPolicy<StringBuilder>
+    public class StringBuilderPooledObjectPolicy : PooledObjectPolicy<StringBuilder>
     {
         public int InitialCapacity { get; set; } = 100;
 
         public int MaximumRetainedCapacity { get; set; } = 4 * 1024;
 
-        public StringBuilder Create()
+        public override StringBuilder Create()
         {
             return new StringBuilder(InitialCapacity);
         }
 
-        public bool Return(StringBuilder obj)
+        public override bool Return(StringBuilder obj)
         {
             if (obj.Capacity > MaximumRetainedCapacity)
             {

test/Microsoft.Extensions.ObjectPool.Test/DefaultObjectPoolTest.cs

@@ -10,6 +10,22 @@ namespace Microsoft.Extensions.ObjectPool.Test
 {
     public class DefaultObjectPoolTest
     {
+        [Fact]
+        public void DefaultObjectPoolWithDefaultPolicy_GetAnd_ReturnObject_SameInstance()
+        {
+            // Arrange
+            var pool = new DefaultObjectPool<object>(new DefaultPooledObjectPolicy<object>());
+
+            var obj1 = pool.Get();
+            pool.Return(obj1);
+
+            // Act
+            var obj2 = pool.Get();
+
+            // Assert
+            Assert.Same(obj1, obj2);
+        }
+
         [Fact]
         public void DefaultObjectPool_GetAndReturnObject_SameInstance()
         {