From 887a3a9f807a72d0ce3d20a5805547a4ef8c37a8 Mon Sep 17 00:00:00 2001
From: David Fowler <davidfowl@gmail.com>
Date: Tue, 22 Jun 2021 08:30:13 -0700
Subject: [PATCH] Improve performance of IsRootScope check - Stash a field
 instead of doing an equality comparison.

Fixes #54351
---
 .../src/ServiceLookup/ServiceProviderEngineScope.cs          | 5 +++--
 .../src/ServiceProvider.cs                                   | 4 ++--
 .../tests/DI.Tests/ServiceProviderEngineScopeTests.cs        | 2 +-
 3 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/ServiceProviderEngineScope.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/ServiceProviderEngineScope.cs
index 06498ff98baac..4ad8b1579a029 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/ServiceProviderEngineScope.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceLookup/ServiceProviderEngineScope.cs
@@ -16,10 +16,11 @@ internal sealed class ServiceProviderEngineScope : IServiceScope, IServiceProvid
         private bool _disposed;
         private List<object> _disposables;
 
-        public ServiceProviderEngineScope(ServiceProvider provider)
+        public ServiceProviderEngineScope(ServiceProvider provider, bool isRootScope)
         {
             ResolvedServices = new Dictionary<ServiceCacheKey, object>();
             RootProvider = provider;
+            IsRootScope = isRootScope;
         }
 
         internal Dictionary<ServiceCacheKey, object> ResolvedServices { get; }
@@ -29,7 +30,7 @@ public ServiceProviderEngineScope(ServiceProvider provider)
         // For other scopes, it protects ResolvedServices and the list of disposables
         internal object Sync => ResolvedServices;
 
-        public bool IsRootScope => this == RootProvider.Root;
+        public bool IsRootScope { get; }
 
         internal ServiceProvider RootProvider { get; }
 
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs
index d21d9807f5f77..fb7052ec8ea66 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/src/ServiceProvider.cs
@@ -36,7 +36,7 @@ internal ServiceProvider(IEnumerable<ServiceDescriptor> serviceDescriptors, Serv
             _createServiceAccessor = CreateServiceAccessor;
             _realizedServices = new ConcurrentDictionary<Type, Func<ServiceProviderEngineScope, object>>();
 
-            Root = new ServiceProviderEngineScope(this);
+            Root = new ServiceProviderEngineScope(this, isRootScope: true);
             CallSiteFactory = new CallSiteFactory(serviceDescriptors);
             // The list of built in services that aren't part of the list of service descriptors
             // keep this in sync with CallSiteFactory.IsService
@@ -173,7 +173,7 @@ internal IServiceScope CreateScope()
                 ThrowHelper.ThrowObjectDisposedException();
             }
 
-            return new ServiceProviderEngineScope(this);
+            return new ServiceProviderEngineScope(this, isRootScope: false);
         }
 
         private ServiceProviderEngine GetEngine()
diff --git a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderEngineScopeTests.cs b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderEngineScopeTests.cs
index 5c19caa922e76..d43752db21eba 100644
--- a/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderEngineScopeTests.cs
+++ b/src/libraries/Microsoft.Extensions.DependencyInjection/tests/DI.Tests/ServiceProviderEngineScopeTests.cs
@@ -12,7 +12,7 @@ public class ServiceProviderEngineScopeTests
         public void DoubleDisposeWorks()
         {
             var provider = new ServiceProvider(new ServiceCollection(), ServiceProviderOptions.Default);
-            var serviceProviderEngineScope = new ServiceProviderEngineScope(provider);
+            var serviceProviderEngineScope = new ServiceProviderEngineScope(provider, isRootScope: true);
             serviceProviderEngineScope.ResolvedServices.Add(new ServiceCacheKey(typeof(IFakeService), 0), null);
             serviceProviderEngineScope.Dispose();
             serviceProviderEngineScope.Dispose();