Annotate ObjectPool with nullable

src/ObjectPool/ref/Microsoft.Extensions.ObjectPool.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(DefaultNetCoreTargetFramework)</TargetFrameworks>
     <TargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true'">$(DefaultNetCoreTargetFramework)</TargetFrameworks>
+    <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="Microsoft.Extensions.ObjectPool.netstandard2.0.cs" />

src/ObjectPool/ref/Microsoft.Extensions.ObjectPool.netcoreapp.cs

@@ -22,7 +22,7 @@ public DefaultPooledObjectPolicy() { }
         public override T Create() { throw null; }
         public override bool Return(T obj) { throw null; }
     }
-    public partial interface IPooledObjectPolicy<T>
+    public partial interface IPooledObjectPolicy<T> where T : notnull
     {
         T Create();
         bool Return(T obj);
@@ -40,7 +40,7 @@ public override void Return(T obj) { }
     }
     public static partial class ObjectPool
     {
-        public static Microsoft.Extensions.ObjectPool.ObjectPool<T> Create<T>(Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T> policy = null) where T : class, new() { throw null; }
+        public static Microsoft.Extensions.ObjectPool.ObjectPool<T> Create<T>(Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T>? policy = null) where T : class, new() { throw null; }
     }
     public abstract partial class ObjectPoolProvider
     {
@@ -59,7 +59,7 @@ protected ObjectPool() { }
         public abstract T Get();
         public abstract void Return(T obj);
     }
-    public abstract partial class PooledObjectPolicy<T> : Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T>
+    public abstract partial class PooledObjectPolicy<T> : Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T> where T : notnull
     {
         protected PooledObjectPolicy() { }
         public abstract T Create();

src/ObjectPool/ref/Microsoft.Extensions.ObjectPool.netstandard2.0.cs

@@ -22,7 +22,7 @@ public DefaultPooledObjectPolicy() { }
         public override T Create() { throw null; }
         public override bool Return(T obj) { throw null; }
     }
-    public partial interface IPooledObjectPolicy<T>
+    public partial interface IPooledObjectPolicy<T> where T : notnull
     {
         T Create();
         bool Return(T obj);
@@ -40,7 +40,7 @@ public override void Return(T obj) { }
     }
     public static partial class ObjectPool
     {
-        public static Microsoft.Extensions.ObjectPool.ObjectPool<T> Create<T>(Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T> policy = null) where T : class, new() { throw null; }
+        public static Microsoft.Extensions.ObjectPool.ObjectPool<T> Create<T>(Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T>? policy = null) where T : class, new() { throw null; }
     }
     public abstract partial class ObjectPoolProvider
     {
@@ -59,7 +59,7 @@ protected ObjectPool() { }
         public abstract T Get();
         public abstract void Return(T obj);
     }
-    public abstract partial class PooledObjectPolicy<T> : Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T>
+    public abstract partial class PooledObjectPolicy<T> : Microsoft.Extensions.ObjectPool.IPooledObjectPolicy<T> where T : notnull
     {
         protected PooledObjectPolicy() { }
         public abstract T Create();

src/ObjectPool/src/DefaultObjectPool.cs

@@ -1,8 +1,9 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.
 
 using System;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Threading;
 
@@ -18,10 +19,10 @@ public class DefaultObjectPool<T> : ObjectPool<T> where T : class
         private protected readonly ObjectWrapper[] _items;
         private protected readonly IPooledObjectPolicy<T> _policy;
         private protected readonly bool _isDefaultPolicy;
-        private protected T _firstItem;
+        private protected T? _firstItem;
 
         // This class was introduced in 2.1 to avoid the interface call where possible
-        private protected readonly PooledObjectPolicy<T> _fastPolicy;
+        private protected readonly PooledObjectPolicy<T>? _fastPolicy;
 
         /// <summary>
         /// Creates an instance of <see cref="DefaultObjectPool{T}"/>.
@@ -97,7 +98,7 @@ public override void Return(T obj)
         [DebuggerDisplay("{Element}")]
         private protected struct ObjectWrapper
         {
-            public T Element;
+            public T? Element;
         }
     }
 }

src/ObjectPool/src/DisposableObjectPool.cs

@@ -1,8 +1,7 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.
 
 using System;
-using System.Runtime.CompilerServices;
 using System.Threading;
 
 namespace Microsoft.Extensions.ObjectPool
@@ -82,7 +81,7 @@ public void Dispose()
             }
         }
 
-        private void DisposeItem(T item)
+        private void DisposeItem(T? item)
         {
             if (item is IDisposable disposable)
             {

src/ObjectPool/src/IPooledObjectPolicy.cs

@@ -7,7 +7,7 @@ namespace Microsoft.Extensions.ObjectPool
     /// Represents a policy for managing pooled objects.
     /// </summary>
     /// <typeparam name="T">The type of object which is being pooled.</typeparam>
-    public interface IPooledObjectPolicy<T>
+    public interface IPooledObjectPolicy<T> where T : notnull
     {
         /// <summary>
         /// Create a <typeparamref name="T"/>.

src/ObjectPool/src/LeakTrackingObjectPool.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.
 
 using System;
@@ -31,8 +31,7 @@ public override T Get()
 
         public override void Return(T obj)
         {
-            Tracker tracker;
-            if (_trackers.TryGetValue(obj, out tracker))
+            if (_trackers.TryGetValue(obj, out var tracker))
             {
                 _trackers.Remove(obj);
                 tracker.Dispose();

src/ObjectPool/src/Microsoft.Extensions.ObjectPool.csproj

@@ -8,6 +8,7 @@
     <PackageTags>pooling</PackageTags>
     <IsPackable>true</IsPackable>
     <IsAspNetCoreApp>true</IsAspNetCoreApp>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/ObjectPool/src/ObjectPool.cs

@@ -1,6 +1,8 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace Microsoft.Extensions.ObjectPool
 {
     /// <summary>
@@ -28,7 +30,7 @@ public abstract class ObjectPool<T> where T : class
     public static class ObjectPool
     {
         /// <inheritdoc />
-        public static ObjectPool<T> Create<T>(IPooledObjectPolicy<T> policy = null) where T : class, new()
+        public static ObjectPool<T> Create<T>(IPooledObjectPolicy<T>? policy = null) where T : class, new()
         {
             var provider = new DefaultObjectPoolProvider();
             return provider.Create(policy ?? new DefaultPooledObjectPolicy<T>());

src/ObjectPool/src/PooledObjectPolicy.cs

@@ -3,7 +3,7 @@
 
 namespace Microsoft.Extensions.ObjectPool
 {
-    public abstract class PooledObjectPolicy<T> : IPooledObjectPolicy<T>
+    public abstract class PooledObjectPolicy<T> : IPooledObjectPolicy<T> where T : notnull
     {
         public abstract T Create();
 

src/ObjectPool/test/Microsoft.Extensions.ObjectPool.Tests.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>$(DefaultNetCoreTargetFramework);net472</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/ObjectPool/test/ThreadingTest.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.
 
 using System.Threading;
@@ -8,8 +8,8 @@ namespace Microsoft.Extensions.ObjectPool
 {
     public class ThreadingTest
     {
-        private CancellationTokenSource _cts;
-        private DefaultObjectPool<Item> _pool;
+        private CancellationTokenSource _cts = default!;
+        private DefaultObjectPool<Item> _pool = default!;
         private bool _foundError;
 
         [Fact]