Fix #6102 - Intense CPU utilization on page change (#6542)

* Fix #6102 - Intense CPU utilization on page change

The issue here was that every time a Razor Page changed, we would
subscribe an additional time to the endpoint change notifications. This
means that if you tweaked a page 30 times, we would update the address
table 31 times when you save the file. If you were doing a lot of editing
then this would grow to a really large amount of computation.

The fix is to use DataSourceDependentCache, which is an existing utility
type we developed for this purpose. I'm not sure why it wasn't being
used for this already. We're already using DataSourceDependentCache in a
bunch of other places, and it's well tested.

I also tweaked the stucture of this code to be more similar to
EndpointNameAddressScheme. This involved some test changes that all
seemed like good cleanup. The way this was being tested was a little
wonky.

(cherry picked from commit a5658a8)

Author: rynowak

src/Http/Routing/src/DataSourceDependentCache.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;
@@ -8,7 +8,7 @@
 
 namespace Microsoft.AspNetCore.Routing
 {
-    internal class DataSourceDependentCache<T> where T : class
+    internal sealed class DataSourceDependentCache<T> : IDisposable where T : class
     {
         private readonly EndpointDataSource _dataSource;
         private readonly Func<IReadOnlyList<Endpoint>, T> _initializeCore;
@@ -19,13 +19,21 @@ internal class DataSourceDependentCache<T> where T : class
         private bool _initialized;
         private T _value;
 
+        private IDisposable _disposable;
+        private bool _disposed;
+
         public DataSourceDependentCache(EndpointDataSource dataSource, Func<IReadOnlyList<Endpoint>, T> initialize)
         {
             if (dataSource == null)
             {
                 throw new ArgumentNullException(nameof(dataSource));
             }
 
+            if (initialize == null)
+            {
+                throw new ArgumentNullException(nameof(initialize));
+            }
+
             _dataSource = dataSource;
             _initializeCore = initialize;
 
@@ -51,9 +59,32 @@ private T Initialize()
                 var changeToken = _dataSource.GetChangeToken();
                 _value = _initializeCore(_dataSource.Endpoints);
 
-                changeToken.RegisterChangeCallback(_initializerWithState, null);
+                // Don't resubscribe if we're already disposed.
+                if (_disposed)
+                {
+                    return _value;
+                }
+
+                _disposable = changeToken.RegisterChangeCallback(_initializerWithState, null);
                 return _value;
             }
         }
+
+        public void Dispose()
+        {
+            lock (_lock)
+            {
+                if (!_disposed)
+                {
+                    _disposable?.Dispose();
+                    _disposable = null;
+
+                    // Tracking whether we're disposed or not prevents a race-condition
+                    // between disposal and Initialize(). If a change callback fires after
+                    // we dispose, then we don't want to reregister.
+                    _disposed = true;
+                }
+            }
+        }
     }
 }

src/Http/Routing/src/DefaultLinkGenerator.cs

@@ -19,7 +19,7 @@
 
 namespace Microsoft.AspNetCore.Routing
 {
-    internal sealed class DefaultLinkGenerator : LinkGenerator
+    internal sealed class DefaultLinkGenerator : LinkGenerator, IDisposable
     {
         private readonly ParameterPolicyFactory _parameterPolicyFactory;
         private readonly ObjectPool<UriBuildingContext> _uriBuildingContextPool;
@@ -364,6 +364,11 @@ public static RouteValueDictionary GetAmbientValues(HttpContext httpContext)
             return httpContext?.Features.Get<IRouteValuesFeature>()?.RouteValues;
         }
 
+        public void Dispose()
+        {
+            _cache.Dispose();
+        }
+
         private static class Log
         {
             public static class EventIds

src/Http/Routing/src/DependencyInjection/RoutingServiceCollectionExtensions.cs

@@ -66,6 +66,7 @@ public static IServiceCollection AddRouting(this IServiceCollection services)
             services.TryAddSingleton<MatcherFactory, DfaMatcherFactory>();
             services.TryAddTransient<DfaMatcherBuilder>();
             services.TryAddSingleton<DfaGraphWriter>();
+            services.TryAddTransient<DataSourceDependentMatcher.Lifetime>();
 
             // Link generation related services
             services.TryAddSingleton<LinkGenerator, DefaultLinkGenerator>();
@@ -77,7 +78,6 @@ public static IServiceCollection AddRouting(this IServiceCollection services)
             //
             services.TryAddSingleton<EndpointSelector, DefaultEndpointSelector>();
             services.TryAddEnumerable(ServiceDescriptor.Singleton<MatcherPolicy, HttpMethodMatcherPolicy>());
-
             return services;
         }
 

src/Http/Routing/src/EndpointNameAddressScheme.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;
@@ -9,7 +9,7 @@
 
 namespace Microsoft.AspNetCore.Routing
 {
-    internal class EndpointNameAddressScheme : IEndpointAddressScheme<string>
+    internal sealed class EndpointNameAddressScheme : IEndpointAddressScheme<string>, IDisposable
     {
         private readonly DataSourceDependentCache<Dictionary<string, Endpoint[]>> _cache;
 
@@ -103,5 +103,10 @@ string GetEndpointName(Endpoint endpoint)
                 return endpoint.Metadata.GetMetadata<IEndpointNameMetadata>()?.EndpointName;
             }
         }
+
+        public void Dispose()
+        {
+            _cache.Dispose();
+        }
     }
 }

src/Http/Routing/src/Matching/DataSourceDependentMatcher.cs

@@ -1,27 +1,31 @@
-// 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.Collections.Generic;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
-using Microsoft.AspNetCore.Http.Features;
 
 namespace Microsoft.AspNetCore.Routing.Matching
 {
-    internal class DataSourceDependentMatcher : Matcher
+    internal sealed class DataSourceDependentMatcher : Matcher
     {
         private readonly Func<MatcherBuilder> _matcherBuilderFactory;
         private readonly DataSourceDependentCache<Matcher> _cache;
 
         public DataSourceDependentMatcher(
             EndpointDataSource dataSource,
+            Lifetime lifetime,
             Func<MatcherBuilder> matcherBuilderFactory)
         {
             _matcherBuilderFactory = matcherBuilderFactory;
 
             _cache = new DataSourceDependentCache<Matcher>(dataSource, CreateMatcher);
             _cache.EnsureInitialized();
+
+            // This will Dispose the cache when the lifetime is disposed, this allows
+            // the service provider to manage the lifetime of the cache.
+            lifetime.Cache = _cache;
         }
 
         // Used in tests
@@ -48,5 +52,41 @@ private Matcher CreateMatcher(IReadOnlyList<Endpoint> endpoints)
 
             return builder.Build();
         }
+
+        // Used to tie the lifetime of a DataSourceDependentCache to the service provider
+        public sealed class Lifetime : IDisposable
+        {
+            private readonly object _lock = new object();
+            private DataSourceDependentCache<Matcher> _cache;
+            private bool _disposed;
+
+            public DataSourceDependentCache<Matcher> Cache
+            {
+                get => _cache;
+                set
+                {
+                    lock (_lock)
+                    {
+                        if (_disposed)
+                        {
+                            value?.Dispose();
+                        }
+
+                        _cache = value;
+                    }
+                }
+            }
+
+            public void Dispose()
+            {
+                lock (_lock)
+                {
+                    _cache?.Dispose();
+                    _cache = null;
+
+                    _disposed = true;
+                }
+            }
+        }
     }
 }

src/Http/Routing/src/Matching/DfaMatcherFactory.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;
@@ -29,7 +29,11 @@ public override Matcher CreateMatcher(EndpointDataSource dataSource)
                 throw new ArgumentNullException(nameof(dataSource));
             }
 
-            return new DataSourceDependentMatcher(dataSource, () =>
+            // Creates a tracking entry in DI to stop listening for change events
+            // when the services are disposed.
+            var lifetime = _services.GetRequiredService<DataSourceDependentMatcher.Lifetime>();
+
+            return new DataSourceDependentMatcher(dataSource, lifetime, () =>
             {
                 return _services.GetRequiredService<DfaMatcherBuilder>();
             });