CopyOnWriteRegistry: Pick the correct registry to dispose.

When the registry hasn't been touched, nothing needs to be disposed. Only when
the registry has been modified, and hence a new (write) registry allocated,
should the registry be disposed. This is determined by the _writeRegistry
field being non-null.

Fixes Resharper warnings in that class.

Issue autofac#746

src/Autofac/Core/Registration/CopyOnWriteRegistry.cs

@@ -46,12 +46,9 @@ internal class CopyOnWriteRegistry : IComponentRegistry
 
         public CopyOnWriteRegistry(IComponentRegistry readRegistry, Func<IComponentRegistry> createWriteRegistry)
         {
-            if (readRegistry == null) throw new ArgumentNullException(nameof(readRegistry));
-            if (createWriteRegistry == null) throw new ArgumentNullException(nameof(createWriteRegistry));
-
-            _readRegistry = readRegistry;
-            _createWriteRegistry = createWriteRegistry;
-            this.Properties = new FallbackDictionary<string, object>(readRegistry.Properties);
+            _readRegistry = readRegistry ?? throw new ArgumentNullException(nameof(readRegistry));
+            _createWriteRegistry = createWriteRegistry ?? throw new ArgumentNullException(nameof(createWriteRegistry));
+            Properties = new FallbackDictionary<string, object>(readRegistry.Properties);
         }
 
         private IComponentRegistry Registry => _writeRegistry ?? _readRegistry;
@@ -69,7 +66,9 @@ public CopyOnWriteRegistry(IComponentRegistry readRegistry, Func<IComponentRegis
 
         public void Dispose()
         {
-            _readRegistry?.Dispose();
+            // The _readRegistry doesn't need to be disposed if it still points to the initial registry.
+            // Only the potentially allocated registry, containing additional registrations, needs to be disposed.
+            _writeRegistry?.Dispose();
         }
 
         public bool TryGetRegistration(Service service, out IComponentRegistration registration)
@@ -101,8 +100,8 @@ public IEnumerable<IComponentRegistration> RegistrationsFor(Service service)
 
         public event EventHandler<ComponentRegisteredEventArgs> Registered
         {
-            add { WriteRegistry.Registered += value; }
-            remove { WriteRegistry.Registered -= value; }
+            add => WriteRegistry.Registered += value;
+            remove => WriteRegistry.Registered -= value;
         }
 
         public void AddRegistrationSource(IRegistrationSource source)
@@ -116,8 +115,8 @@ public void AddRegistrationSource(IRegistrationSource source)
 
         public event EventHandler<RegistrationSourceAddedEventArgs> RegistrationSourceAdded
         {
-            add { WriteRegistry.RegistrationSourceAdded += value; }
-            remove { WriteRegistry.RegistrationSourceAdded -= value; }
+            add => WriteRegistry.RegistrationSourceAdded += value;
+            remove => WriteRegistry.RegistrationSourceAdded -= value;
         }
     }
 }

test/Autofac.Test/Core/Registration/CopyOnWriteRegistryTests.cs

@@ -48,5 +48,19 @@ public void RegistrationsMadeByUpdatingAChildScopeDoNotAppearInTheParentScope()
             Assert.True(childScope.IsRegistered<object>());
             Assert.False(container.IsRegistered<object>());
         }
+
+        [Fact]
+        public void OnlyRegistrationsMadeOnTheRegistryAreDisposedWhenTheRegistryIsDisposed()
+        {
+            var componentRegistration = Mocks.GetComponentRegistration();
+            var readOnlyRegistry = new ComponentRegistry();
+            readOnlyRegistry.Register(componentRegistration);
+            var cow = new CopyOnWriteRegistry(readOnlyRegistry, () => new ComponentRegistry());
+            var nestedComponentRegistration = Mocks.GetComponentRegistration();
+            cow.Register(nestedComponentRegistration);
+            cow.Dispose();
+            Assert.False(componentRegistration.IsDisposed);
+            Assert.True(nestedComponentRegistration.IsDisposed);
+        }
     }
 }

test/Autofac.Test/Mocks.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.Reflection;
+using Autofac.Core;
 using Autofac.Core.Activators.Reflection;
 
 namespace Autofac.Test
@@ -21,6 +23,11 @@ public static Startable GetStartable()
             return new Startable();
         }
 
+        public static MockComponentRegistration GetComponentRegistration()
+        {
+            return new MockComponentRegistration();
+        }
+
         internal class MockConstructorFinder : IConstructorFinder
         {
             public ConstructorInfo[] FindConstructors(Type targetType)
@@ -46,5 +53,49 @@ public void Start()
                 StartCount++;
             }
         }
+
+        internal class MockComponentRegistration : IComponentRegistration
+        {
+            public void Dispose()
+            {
+                IsDisposed = true;
+            }
+
+            public bool IsDisposed { get; set; }
+
+            public Guid Id { get; }
+
+            public IInstanceActivator Activator { get; }
+
+            public IComponentLifetime Lifetime { get; }
+
+            public InstanceSharing Sharing { get; }
+
+            public InstanceOwnership Ownership { get; }
+
+            public IEnumerable<Service> Services { get; } = new Service[0];
+
+            public IDictionary<string, object> Metadata { get; }
+
+            public IComponentRegistration Target { get; }
+
+            public event EventHandler<PreparingEventArgs> Preparing;
+
+            public void RaisePreparing(IComponentContext context, ref IEnumerable<Parameter> parameters)
+            {
+            }
+
+            public event EventHandler<ActivatingEventArgs<object>> Activating;
+
+            public void RaiseActivating(IComponentContext context, IEnumerable<Parameter> parameters, ref object instance)
+            {
+            }
+
+            public event EventHandler<ActivatedEventArgs<object>> Activated;
+
+            public void RaiseActivated(IComponentContext context, IEnumerable<Parameter> parameters, object instance)
+            {
+            }
+        }
     }
 }