[Mvc] Fix global state in controller and action endpoint data sources.

* Create data sources "per router" instance.
* Make a global shared order sequence "per router" for conventional and
  controller and page routes.
* Create DynamicControllerEndpointSelector and DynamicPageEndpointSelector
  instances per data source.

src/Mvc/Mvc.Core/src/Builder/ControllerEndpointRouteBuilderExtensions.cs

@@ -5,10 +5,10 @@ using System;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc.Core;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Routing;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Constraints;
-using Microsoft.AspNetCore.Routing.Patterns;
 using Microsoft.Extensions.DependencyInjection;
 
 namespace Microsoft.AspNetCore.Builder
@@ -213,7 +213,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureControllerServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var dataSource = GetOrCreateDataSource(endpoints);
+            dataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, dataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -222,6 +224,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicControllerMetadata(action, controller, area: null));
+                b.Metadata.Add(new ControllerEndpointDataSourceIdMetadata(dataSource.DataSourceId));
             });
             return builder;
         }
@@ -289,7 +292,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureControllerServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var dataSource = GetOrCreateDataSource(endpoints);
+            dataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, dataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -298,6 +303,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicControllerMetadata(action, controller, area: null));
+                b.Metadata.Add(new ControllerEndpointDataSourceIdMetadata(dataSource.DataSourceId));
             });
             return builder;
         }
@@ -357,7 +363,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureControllerServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var dataSource = GetOrCreateDataSource(endpoints);
+            dataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, dataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -366,6 +374,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicControllerMetadata(action, controller, area));
+                b.Metadata.Add(new ControllerEndpointDataSourceIdMetadata(dataSource.DataSourceId));
             });
             return builder;
         }
@@ -435,7 +444,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureControllerServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var dataSource = GetOrCreateDataSource(endpoints);
+            dataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, dataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -444,6 +455,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicControllerMetadata(action, controller, area));
+                b.Metadata.Add(new ControllerEndpointDataSourceIdMetadata(dataSource.DataSourceId));
             });
             return builder;
         }
@@ -507,11 +519,50 @@ namespace Microsoft.AspNetCore.Builder
 
             // Called for side-effect to make sure that the data source is registered.
             var controllerDataSource = GetOrCreateDataSource(endpoints);
+            RegisterInCache(endpoints.ServiceProvider, controllerDataSource);
 
             // The data source is just used to share the common order with conventionally routed actions.
             controllerDataSource.AddDynamicControllerEndpoint(endpoints, pattern, typeof(TTransformer), state);
         }
 
+        /// <summary>
+        /// Adds a specialized <see cref="RouteEndpoint"/> to the <see cref="IEndpointRouteBuilder"/> that will
+        /// attempt to select a controller action using the route values produced by <typeparamref name="TTransformer"/>.
+        /// </summary>
+        /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add the route to.</param>
+        /// <param name="pattern">The URL pattern of the route.</param>
+        /// <param name="state">A state object to provide to the <typeparamref name="TTransformer" /> instance.</param>
+        /// <param name="order">The matching order for the dynamic route.</param>
+        /// <typeparam name="TTransformer">The type of a <see cref="DynamicRouteValueTransformer"/>.</typeparam>
+        /// <remarks>
+        /// <para>
+        /// This method allows the registration of a <see cref="RouteEndpoint"/> and <see cref="DynamicRouteValueTransformer"/>
+        /// that combine to dynamically select a controller action using custom logic.
+        /// </para>
+        /// <para>
+        /// The instance of <typeparamref name="TTransformer"/> will be retrieved from the dependency injection container.
+        /// Register <typeparamref name="TTransformer"/> as transient in <c>ConfigureServices</c>. Using the transient lifetime
+        /// is required when using <paramref name="state" />.
+        /// </para>
+        /// </remarks>
+        public static void MapDynamicControllerRoute<TTransformer>(this IEndpointRouteBuilder endpoints, string pattern, object state, int order)
+            where TTransformer : DynamicRouteValueTransformer
+        {
+            if (endpoints == null)
+            {
+                throw new ArgumentNullException(nameof(endpoints));
+            }
+
+            EnsureControllerServices(endpoints);
+
+            // Called for side-effect to make sure that the data source is registered.
+            var controllerDataSource = GetOrCreateDataSource(endpoints);
+            RegisterInCache(endpoints.ServiceProvider, controllerDataSource);
+
+            // The data source is just used to share the common order with conventionally routed actions.
+            controllerDataSource.AddDynamicControllerEndpoint(endpoints, pattern, typeof(TTransformer), state, order);
+        }
+
         private static DynamicControllerMetadata CreateDynamicControllerMetadata(string action, string controller, string area)
         {
             return new DynamicControllerMetadata(new RouteValueDictionary()
@@ -539,11 +590,19 @@ namespace Microsoft.AspNetCore.Builder
             var dataSource = endpoints.DataSources.OfType<ControllerActionEndpointDataSource>().FirstOrDefault();
             if (dataSource == null)
             {
-                dataSource = endpoints.ServiceProvider.GetRequiredService<ControllerActionEndpointDataSource>();
+                var orderProvider = endpoints.ServiceProvider.GetRequiredService<OrderedEndpointsSequenceProviderCache>();
+                var factory = endpoints.ServiceProvider.GetRequiredService<ControllerActionEndpointDataSourceFactory>();
+                dataSource = factory.Create(orderProvider.GetOrCreateOrderedEndpointsSequenceProvider(endpoints));
                 endpoints.DataSources.Add(dataSource);
             }
 
             return dataSource;
         }
+
+        private static void RegisterInCache(IServiceProvider serviceProvider, ControllerActionEndpointDataSource dataSource)
+        {
+            var cache = serviceProvider.GetRequiredService<DynamicControllerEndpointSelectorCache>();
+            cache.AddDataSource(dataSource);
+        }
     }
 }

src/Mvc/Mvc.Core/src/DependencyInjection/MvcCoreServiceCollectionExtensions.cs

@@ -269,10 +269,11 @@ namespace Microsoft.Extensions.DependencyInjection
             //
             // Endpoint Routing / Endpoints
             //
-            services.TryAddSingleton<OrderedEndpointsSequenceProvider>();
+            services.TryAddSingleton<ControllerActionEndpointDataSourceFactory>();
-            services.TryAddSingleton<ControllerActionEndpointDataSource>();
+            services.TryAddSingleton<OrderedEndpointsSequenceProviderCache>();
+            services.TryAddSingleton<ControllerActionEndpointDataSourceIdProvider>();
             services.TryAddSingleton<ActionEndpointFactory>();
-            services.TryAddSingleton<DynamicControllerEndpointSelector>();
+            services.TryAddSingleton<DynamicControllerEndpointSelectorCache>();
             services.TryAddEnumerable(ServiceDescriptor.Singleton<MatcherPolicy, DynamicControllerEndpointMatcherPolicy>());
 
             //

src/Mvc/Mvc.Core/src/Infrastructure/OrderedEndpointsSequenceProvider.cs

@@ -1,26 +1,23 @@
 // 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;
+
 namespace Microsoft.AspNetCore.Mvc.Infrastructure
 {
     internal class OrderedEndpointsSequenceProvider
     {
-        private object Lock = new object();
-
         // In traditional conventional routing setup, the routes defined by a user have a order
         // defined by how they are added into the list. We would like to maintain the same order when building
         // up the endpoints too.
         //
         // Start with an order of '1' for conventional routes as attribute routes have a default order of '0'.
         // This is for scenarios dealing with migrating existing Router based code to Endpoint Routing world.
-        private int _current = 1;
+        private int _current = 0;
 
         public int GetNext()
         {
-            lock (Lock)
+            return Interlocked.Increment(ref _current);
-            {
-                return _current++;
-            }
         }
     }
 }

src/Mvc/Mvc.Core/src/Infrastructure/OrderedEndpointsSequenceProviderCache.cs

@@ -0,0 +1,18 @@
+// 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.Collections.Concurrent;
+using Microsoft.AspNetCore.Routing;
+
+namespace Microsoft.AspNetCore.Mvc.Infrastructure
+{
+    internal class OrderedEndpointsSequenceProviderCache
+    {
+        private readonly ConcurrentDictionary<IEndpointRouteBuilder, OrderedEndpointsSequenceProvider> _sequenceProviderCache = new();
+
+        public OrderedEndpointsSequenceProvider GetOrCreateOrderedEndpointsSequenceProvider(IEndpointRouteBuilder endpoints)
+        {
+            return _sequenceProviderCache.GetOrAdd(endpoints, new OrderedEndpointsSequenceProvider());
+        }
+    }
+}

src/Mvc/Mvc.Core/src/Routing/ControllerActionEndpointDataSource.cs

@@ -19,13 +19,17 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         private readonly List<ConventionalRouteEntry> _routes;
 
         public ControllerActionEndpointDataSource(
+            ControllerActionEndpointDataSourceIdProvider dataSourceIdProvider,
             IActionDescriptorCollectionProvider actions,
             ActionEndpointFactory endpointFactory,
             OrderedEndpointsSequenceProvider orderSequence)
             : base(actions)
         {
             _endpointFactory = endpointFactory;
+
+            DataSourceId = dataSourceIdProvider.CreateId();
             _orderSequence = orderSequence;
+
             _routes = new List<ConventionalRouteEntry>();
 
             DefaultBuilder = new ControllerActionEndpointConventionBuilder(Lock, Conventions);
@@ -35,6 +39,8 @@ namespace Microsoft.AspNetCore.Mvc.Routing
             Subscribe();
         }
 
+        public int DataSourceId { get; }
+
         public ControllerActionEndpointConventionBuilder DefaultBuilder { get; }
 
         // Used to control whether we create 'inert' (non-routable) endpoints for use in dynamic
@@ -101,12 +107,12 @@ namespace Microsoft.AspNetCore.Mvc.Routing
             return endpoints;
         }
 
-        internal void AddDynamicControllerEndpoint(IEndpointRouteBuilder endpoints, string pattern, Type transformerType, object state)
+        internal void AddDynamicControllerEndpoint(IEndpointRouteBuilder endpoints, string pattern, Type transformerType, object state, int? order = null)
         {
             CreateInertEndpoints = true;
             lock (Lock)
             {
-                var order = _orderSequence.GetNext();
+                order ??= _orderSequence.GetNext();
 
                 endpoints.Map(
                     pattern,
@@ -116,8 +122,9 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                     })
                     .Add(b =>
                     {
-                        ((RouteEndpointBuilder)b).Order = order;
+                        ((RouteEndpointBuilder)b).Order = order.Value;
                         b.Metadata.Add(new DynamicControllerRouteValueTransformerMetadata(transformerType, state));
+                        b.Metadata.Add(new ControllerEndpointDataSourceIdMetadata(DataSourceId));
                     });
             }
         }

src/Mvc/Mvc.Core/src/Routing/ControllerActionEndpointDataSourceFactory.cs

@@ -0,0 +1,29 @@
+// 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 Microsoft.AspNetCore.Mvc.Routing;
+
+namespace Microsoft.AspNetCore.Mvc.Infrastructure
+{
+    internal class ControllerActionEndpointDataSourceFactory
+    {
+        private readonly ControllerActionEndpointDataSourceIdProvider _dataSourceIdProvider;
+        private readonly IActionDescriptorCollectionProvider _actions;
+        private readonly ActionEndpointFactory _factory;
+
+        public ControllerActionEndpointDataSourceFactory(
+            ControllerActionEndpointDataSourceIdProvider dataSourceIdProvider,
+            IActionDescriptorCollectionProvider actions,
+            ActionEndpointFactory factory)
+        {
+            _dataSourceIdProvider = dataSourceIdProvider;
+            _actions = actions;
+            _factory = factory;
+        }
+
+        public ControllerActionEndpointDataSource Create(OrderedEndpointsSequenceProvider orderProvider)
+        {
+            return new ControllerActionEndpointDataSource(_dataSourceIdProvider, _actions, _factory, orderProvider);
+        }
+    }
+}

src/Mvc/Mvc.Core/src/Routing/ControllerActionEndpointDataSourceIdProvider.cs

@@ -0,0 +1,17 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Mvc.Routing
+{
+    internal class ControllerActionEndpointDataSourceIdProvider
+    {
+        private int _nextId = 1;
+
+        internal int CreateId()
+        {
+            return Interlocked.Increment(ref _nextId);
+        }
+    }
+}

src/Mvc/Mvc.Core/src/Routing/ControllerEndpointDataSourceIdMetadata.cs

@@ -0,0 +1,15 @@
+// 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.AspNetCore.Mvc.Routing
+{
+    internal class ControllerEndpointDataSourceIdMetadata
+    {
+        public ControllerEndpointDataSourceIdMetadata(int id)
+        {
+            Id = id;
+        }
+
+        public int Id { get; }
+    }
+}

src/Mvc/Mvc.Core/src/Routing/DynamicControllerEndpointMatcherPolicy.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
@@ -15,14 +16,14 @@ namespace Microsoft.AspNetCore.Mvc.Routing
 {
     internal class DynamicControllerEndpointMatcherPolicy : MatcherPolicy, IEndpointSelectorPolicy
     {
-        private readonly DynamicControllerEndpointSelector _selector;
+        private readonly DynamicControllerEndpointSelectorCache _selectorCache;
         private readonly EndpointMetadataComparer _comparer;
 
-        public DynamicControllerEndpointMatcherPolicy(DynamicControllerEndpointSelector selector, EndpointMetadataComparer comparer)
+        public DynamicControllerEndpointMatcherPolicy(DynamicControllerEndpointSelectorCache selectorCache, EndpointMetadataComparer comparer)
         {
-            if (selector == null)
+            if (selectorCache == null)
             {
-                throw new ArgumentNullException(nameof(selector));
+                throw new ArgumentNullException(nameof(selectorCache));
             }
 
             if (comparer == null)
@@ -30,7 +31,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                 throw new ArgumentNullException(nameof(comparer));
             }
 
-            _selector = selector;
+            _selectorCache = selectorCache;
             _comparer = comparer;
         }
 
@@ -79,6 +80,9 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                 throw new ArgumentNullException(nameof(candidates));
             }
 
+            // The per-route selector, must be the same for all the endpoints we are dealing with.
+            DynamicControllerEndpointSelector selector = null;
+
             // There's no real benefit here from trying to avoid the async state machine.
             // We only execute on nodes that contain a dynamic policy, and thus always have
             // to await something.
@@ -127,7 +131,9 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                     continue;
                 }
 
-                var endpoints = _selector.SelectEndpoints(dynamicValues);
+                selector = ResolveSelector(selector, endpoint);
+
+                var endpoints = selector.SelectEndpoints(dynamicValues);
                 if (endpoints.Count == 0 && dynamicControllerMetadata != null)
                 {
                     // Naving no match for a fallback is a configuration error. We can't really check
@@ -172,5 +178,14 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                 candidates.ExpandEndpoint(i, endpoints, _comparer);
             }
         }
+
+        private DynamicControllerEndpointSelector ResolveSelector(DynamicControllerEndpointSelector currentSelector, Endpoint endpoint)
+        {
+            var selector = _selectorCache.GetEndpointSelector(endpoint);
+
+            Debug.Assert(currentSelector == null || ReferenceEquals(currentSelector, selector));
+
+            return selector;
+        }
     }
 }

src/Mvc/Mvc.Core/src/Routing/DynamicControllerEndpointSelector.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;
@@ -11,25 +11,15 @@ namespace Microsoft.AspNetCore.Mvc.Routing
 {
     internal class DynamicControllerEndpointSelector : IDisposable
     {
-        private readonly EndpointDataSource _dataSource;
         private readonly DataSourceDependentCache<ActionSelectionTable<Endpoint>> _cache;
 
-        public DynamicControllerEndpointSelector(ControllerActionEndpointDataSource dataSource)
+        public DynamicControllerEndpointSelector(EndpointDataSource dataSource)
-            : this((EndpointDataSource)dataSource)
-        {
-        }
-
-        // Exposed for tests. We need to accept a more specific type in the constructor for DI
-        // to work.
-        protected DynamicControllerEndpointSelector(EndpointDataSource dataSource)
         {
             if (dataSource == null)
             {
                 throw new ArgumentNullException(nameof(dataSource));
             }
 
-            _dataSource = dataSource;
-
             _cache = new DataSourceDependentCache<ActionSelectionTable<Endpoint>>(dataSource, Initialize);
         }
 

src/Mvc/Mvc.Core/src/Routing/DynamicControllerEndpointSelectorCache.cs

@@ -0,0 +1,46 @@
+// 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.Concurrent;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+
+namespace Microsoft.AspNetCore.Mvc.Routing
+{
+    internal class DynamicControllerEndpointSelectorCache
+    {
+        private readonly ConcurrentDictionary<int, EndpointDataSource> _dataSourceCache = new();
+        private readonly ConcurrentDictionary<int, DynamicControllerEndpointSelector> _endpointSelectorCache = new();
+
+        public void AddDataSource(ControllerActionEndpointDataSource dataSource)
+        {
+            _dataSourceCache.GetOrAdd(dataSource.DataSourceId, dataSource);
+        }
+
+        // For testing purposes only
+        internal void AddDataSource(EndpointDataSource dataSource, int key) =>
+            _dataSourceCache.GetOrAdd(key, dataSource);
+
+        public DynamicControllerEndpointSelector GetEndpointSelector(Endpoint endpoint)
+        {
+            if (endpoint?.Metadata == null)
+            {
+                return null;
+            }
+
+            var dataSourceId = endpoint.Metadata.GetMetadata<ControllerEndpointDataSourceIdMetadata>();
+            return _endpointSelectorCache.GetOrAdd(dataSourceId.Id, key => EnsureDataSource(key));
+        }
+
+        private DynamicControllerEndpointSelector EnsureDataSource(int key)
+        {
+            if (!_dataSourceCache.TryGetValue(key, out var dataSource))
+            {
+                throw new InvalidOperationException($"Data source with key '{key}' not registered.");
+            }
+
+            return new DynamicControllerEndpointSelector(dataSource);
+        }
+    }
+}

src/Mvc/Mvc.Core/test/Routing/ControllerActionEndpointDataSourceTest.cs

@@ -246,7 +246,6 @@ namespace Microsoft.AspNetCore.Mvc.Routing
             dataSource.AddRoute("1", "/1/{controller}/{action}/{id?}", null, null, null);
             dataSource.AddRoute("2", "/2/{controller}/{action}/{id?}", null, null, null);
 
-            
             dataSource.DefaultBuilder.Add(b =>
             {
                 if (b.Metadata.OfType<ActionDescriptor>().FirstOrDefault()?.AttributeRouteInfo != null)
@@ -385,7 +384,11 @@ namespace Microsoft.AspNetCore.Mvc.Routing
 
         private protected override ActionEndpointDataSourceBase CreateDataSource(IActionDescriptorCollectionProvider actions, ActionEndpointFactory endpointFactory)
         {
-            return new ControllerActionEndpointDataSource(actions, endpointFactory, new OrderedEndpointsSequenceProvider());
+            return new ControllerActionEndpointDataSource(
+                new ControllerActionEndpointDataSourceIdProvider(),
+                actions,
+                endpointFactory,
+                new OrderedEndpointsSequenceProvider());
         }
 
         protected override ActionDescriptor CreateActionDescriptor(

src/Mvc/Mvc.Core/test/Routing/DynamicControllerEndpointMatcherPolicyTest.cs

@@ -19,6 +19,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
     {
         public DynamicControllerEndpointMatcherPolicyTest()
         {
+            var dataSourceKey = new ControllerEndpointDataSourceIdMetadata(1);
             var actions = new ActionDescriptor[]
             {
                 new ControllerActionDescriptor()
@@ -59,12 +60,13 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                 new EndpointMetadataCollection(new object[]
                 {
                     new DynamicControllerRouteValueTransformerMetadata(typeof(CustomTransformer), State),
+                    dataSourceKey
                 }),
                 "dynamic");
 
             DataSource = new DefaultEndpointDataSource(ControllerEndpoints);
 
-            Selector = new TestDynamicControllerEndpointSelector(DataSource);
+            SelectorCache = new TestDynamicControllerEndpointSelectorCache(DataSource, 1);
 
             var services = new ServiceCollection();
             services.AddRouting();
@@ -88,7 +90,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
 
         private Endpoint DynamicEndpoint { get; }
 
-        private DynamicControllerEndpointSelector Selector { get; }
+        private DynamicControllerEndpointSelectorCache SelectorCache { get; }
 
         private IServiceProvider Services { get; }
 
@@ -102,7 +104,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_NoMatch()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { null, };
@@ -132,7 +134,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_HasMatchNoEndpointFound()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { null, };
@@ -163,7 +165,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_HasMatchFindsEndpoint_WithoutRouteValues()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { null, };
@@ -209,7 +211,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_ThrowsForTransformerWithInvalidLifetime()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -240,7 +242,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_HasMatchFindsEndpoint_WithRouteValues()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -297,7 +299,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_CanDiscardFoundEndpoints()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -336,7 +338,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_CanReplaceFoundEndpoints()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -398,7 +400,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public async Task ApplyAsync_CanExpandTheListOfFoundEndpoints()
         {
             // Arrange
-            var policy = new DynamicControllerEndpointMatcherPolicy(Selector, Comparer);
+            var policy = new DynamicControllerEndpointMatcherPolicy(SelectorCache, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -437,11 +439,11 @@ namespace Microsoft.AspNetCore.Mvc.Routing
             Assert.Same(ControllerEndpoints[2], candidates[1].Endpoint);
         }
 
-        private class TestDynamicControllerEndpointSelector : DynamicControllerEndpointSelector
+        private class TestDynamicControllerEndpointSelectorCache : DynamicControllerEndpointSelectorCache
         {
-            public TestDynamicControllerEndpointSelector(EndpointDataSource dataSource)
+            public TestDynamicControllerEndpointSelectorCache(EndpointDataSource dataSource, int key)
-                : base(dataSource)
             {
+                AddDataSource(dataSource, key);
             }
         }
 

src/Mvc/Mvc.RazorPages/src/Builder/RazorPagesEndpointRouteBuilderExtensions.cs

@@ -5,6 +5,7 @@ using System;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Mvc.ApplicationModels;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Routing;
 using Microsoft.AspNetCore.Routing;
@@ -75,7 +76,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureRazorPagesServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var pageDataSource = GetOrCreateDataSource(endpoints);
+            pageDataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, pageDataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -84,6 +87,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicPageMetadata(page, area: null));
+                b.Metadata.Add(new PageEndpointDataSourceIdMetadata(pageDataSource.DataSourceId));
             });
             return builder;
         }
@@ -141,7 +145,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureRazorPagesServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var pageDataSource = GetOrCreateDataSource(endpoints);
+            pageDataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, pageDataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -150,6 +156,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicPageMetadata(page, area: null));
+                b.Metadata.Add(new PageEndpointDataSourceIdMetadata(pageDataSource.DataSourceId));
             });
             return builder;
         }
@@ -199,7 +206,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureRazorPagesServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var pageDataSource = GetOrCreateDataSource(endpoints);
+            pageDataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, pageDataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -208,6 +217,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicPageMetadata(page, area));
+                b.Metadata.Add(new PageEndpointDataSourceIdMetadata(pageDataSource.DataSourceId));
             });
             return builder;
         }
@@ -267,7 +277,9 @@ namespace Microsoft.AspNetCore.Builder
             EnsureRazorPagesServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            GetOrCreateDataSource(endpoints).CreateInertEndpoints = true;
+            var pageDataSource = GetOrCreateDataSource(endpoints);
+            pageDataSource.CreateInertEndpoints = true;
+            RegisterInCache(endpoints.ServiceProvider, pageDataSource);
 
             // Maps a fallback endpoint with an empty delegate. This is OK because
             // we don't expect the delegate to run.
@@ -276,6 +288,7 @@ namespace Microsoft.AspNetCore.Builder
             {
                 // MVC registers a policy that looks for this metadata.
                 b.Metadata.Add(CreateDynamicPageMetadata(page, area));
+                b.Metadata.Add(new PageEndpointDataSourceIdMetadata(pageDataSource.DataSourceId));
             });
             return builder;
         }
@@ -337,9 +350,51 @@ namespace Microsoft.AspNetCore.Builder
             EnsureRazorPagesServices(endpoints);
 
             // Called for side-effect to make sure that the data source is registered.
-            var dataSource = GetOrCreateDataSource(endpoints);
+            var pageDataSource = GetOrCreateDataSource(endpoints);
+            RegisterInCache(endpoints.ServiceProvider, pageDataSource);
 
-            dataSource.AddDynamicPageEndpoint(endpoints, pattern, typeof(TTransformer), state);
+            pageDataSource.AddDynamicPageEndpoint(endpoints, pattern, typeof(TTransformer), state);
+        }
+
+        /// <summary>
+        /// Adds a specialized <see cref="RouteEndpoint"/> to the <see cref="IEndpointRouteBuilder"/> that will
+        /// attempt to select a page using the route values produced by <typeparamref name="TTransformer"/>.
+        /// </summary>
+        /// <param name="endpoints">The <see cref="IEndpointRouteBuilder"/> to add the route to.</param>
+        /// <param name="pattern">The URL pattern of the route.</param>
+        /// <param name="state">A state object to provide to the <typeparamref name="TTransformer" /> instance.</param>
+        /// <param name="order">The matching order for the dynamic route.</param>
+        /// <typeparam name="TTransformer">The type of a <see cref="DynamicRouteValueTransformer"/>.</typeparam>
+        /// <remarks>
+        /// <para>
+        /// This method allows the registration of a <see cref="RouteEndpoint"/> and <see cref="DynamicRouteValueTransformer"/>
+        /// that combine to dynamically select a page using custom logic.
+        /// </para>
+        /// <para>
+        /// The instance of <typeparamref name="TTransformer"/> will be retrieved from the dependency injection container.
+        /// Register <typeparamref name="TTransformer"/> with the desired service lifetime in <c>ConfigureServices</c>.
+        /// </para>
+        /// </remarks>
+        public static void MapDynamicPageRoute<TTransformer>(this IEndpointRouteBuilder endpoints, string pattern, object state, int order)
+            where TTransformer : DynamicRouteValueTransformer
+        {
+            if (endpoints == null)
+            {
+                throw new ArgumentNullException(nameof(endpoints));
+            }
+
+            if (pattern == null)
+            {
+                throw new ArgumentNullException(nameof(pattern));
+            }
+
+            EnsureRazorPagesServices(endpoints);
+
+            // Called for side-effect to make sure that the data source is registered.
+            var pageDataSource = GetOrCreateDataSource(endpoints);
+            RegisterInCache(endpoints.ServiceProvider, pageDataSource);
+
+            pageDataSource.AddDynamicPageEndpoint(endpoints, pattern, typeof(TTransformer), state, order);
         }
 
         private static DynamicPageMetadata CreateDynamicPageMetadata(string page, string area)
@@ -353,7 +408,7 @@ namespace Microsoft.AspNetCore.Builder
 
         private static void EnsureRazorPagesServices(IEndpointRouteBuilder endpoints)
         {
-            var marker = endpoints.ServiceProvider.GetService<PageActionEndpointDataSource>();
+            var marker = endpoints.ServiceProvider.GetService<PageActionEndpointDataSourceFactory>();
             if (marker == null)
             {
                 throw new InvalidOperationException(Mvc.Core.Resources.FormatUnableToFindServices(
@@ -368,11 +423,19 @@ namespace Microsoft.AspNetCore.Builder
             var dataSource = endpoints.DataSources.OfType<PageActionEndpointDataSource>().FirstOrDefault();
             if (dataSource == null)
             {
-                dataSource = endpoints.ServiceProvider.GetRequiredService<PageActionEndpointDataSource>();
+                var orderProviderCache = endpoints.ServiceProvider.GetRequiredService<OrderedEndpointsSequenceProviderCache>();
+                var factory = endpoints.ServiceProvider.GetRequiredService<PageActionEndpointDataSourceFactory>();
+                dataSource = factory.Create(orderProviderCache.GetOrCreateOrderedEndpointsSequenceProvider(endpoints));
                 endpoints.DataSources.Add(dataSource);
             }
 
             return dataSource;
         }
+
+        private static void RegisterInCache(IServiceProvider serviceProvider, PageActionEndpointDataSource dataSource)
+        {
+            var cache = serviceProvider.GetRequiredService<DynamicPageEndpointSelectorCache>();
+            cache.AddDataSource(dataSource);
+        }
     }
 }

src/Mvc/Mvc.RazorPages/src/DependencyInjection/MvcRazorPagesMvcCoreBuilderExtensions.cs

@@ -89,15 +89,15 @@ namespace Microsoft.Extensions.DependencyInjection
             // Routing
             services.TryAddEnumerable(ServiceDescriptor.Singleton<MatcherPolicy, PageLoaderMatcherPolicy>());
             services.TryAddEnumerable(ServiceDescriptor.Singleton<MatcherPolicy, DynamicPageEndpointMatcherPolicy>());
-            services.TryAddSingleton<DynamicPageEndpointSelector>();
+            services.TryAddSingleton<DynamicPageEndpointSelectorCache>();
+            services.TryAddSingleton<PageActionEndpointDataSourceIdProvider>();
 
             // Action description and invocation
             services.TryAddEnumerable(
                 ServiceDescriptor.Singleton<IActionDescriptorProvider, PageActionDescriptorProvider>());
             services.TryAddEnumerable(
                 ServiceDescriptor.Singleton<IPageRouteModelProvider, CompiledPageRouteModelProvider>());
-            services.TryAddSingleton<PageActionEndpointDataSource>();
+            services.TryAddSingleton<PageActionEndpointDataSourceFactory>();
-            services.TryAddSingleton<DynamicPageEndpointSelector>();
             services.TryAddEnumerable(ServiceDescriptor.Singleton<MatcherPolicy, DynamicPageEndpointMatcherPolicy>());
 
             services.TryAddEnumerable(

src/Mvc/Mvc.RazorPages/src/Infrastructure/DynamicPageEndpointMatcherPolicy.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
@@ -15,15 +16,15 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
 {
     internal class DynamicPageEndpointMatcherPolicy : MatcherPolicy, IEndpointSelectorPolicy
     {
-        private readonly DynamicPageEndpointSelector _selector;
+        private readonly DynamicPageEndpointSelectorCache _selectorCache;
         private readonly PageLoader _loader;
         private readonly EndpointMetadataComparer _comparer;
 
-        public DynamicPageEndpointMatcherPolicy(DynamicPageEndpointSelector selector, PageLoader loader, EndpointMetadataComparer comparer)
+        public DynamicPageEndpointMatcherPolicy(DynamicPageEndpointSelectorCache selectorCache, PageLoader loader, EndpointMetadataComparer comparer)
         {
-            if (selector == null)
+            if (selectorCache == null)
             {
-                throw new ArgumentNullException(nameof(selector));
+                throw new ArgumentNullException(nameof(selectorCache));
             }
 
             if (loader == null)
@@ -36,7 +37,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                 throw new ArgumentNullException(nameof(comparer));
             }
 
-            _selector = selector;
+            _selectorCache = selectorCache;
             _loader = loader;
             _comparer = comparer;
         }
@@ -86,6 +87,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                 throw new ArgumentNullException(nameof(candidates));
             }
 
+            DynamicPageEndpointSelector selector = null;
+
             // There's no real benefit here from trying to avoid the async state machine.
             // We only execute on nodes that contain a dynamic policy, and thus always have
             // to await something.
@@ -132,7 +135,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                     continue;
                 }
 
-                var endpoints = _selector.SelectEndpoints(dynamicValues);
+                selector = ResolveSelector(selector, endpoint);
+                var endpoints = selector.SelectEndpoints(dynamicValues);
                 if (endpoints.Count == 0 && dynamicPageMetadata != null)
                 {
                     // Having no match for a fallback is a configuration error. We can't really check
@@ -196,5 +200,15 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                 candidates.ExpandEndpoint(i, loadedEndpoints, _comparer);
             }
         }
+
+        private DynamicPageEndpointSelector ResolveSelector(DynamicPageEndpointSelector currentSelector, Endpoint endpoint)
+        {
+            var selector = _selectorCache.GetEndpointSelector(endpoint);
+
+            Debug.Assert(currentSelector == null || ReferenceEquals(currentSelector, selector));
+
+            return selector;
+        }
+
     }
 }

src/Mvc/Mvc.RazorPages/src/Infrastructure/DynamicPageEndpointSelector.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;
@@ -14,14 +14,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         private readonly EndpointDataSource _dataSource;
         private readonly DataSourceDependentCache<ActionSelectionTable<Endpoint>> _cache;
 
-        public DynamicPageEndpointSelector(PageActionEndpointDataSource dataSource)
+        public DynamicPageEndpointSelector(EndpointDataSource dataSource)
-            : this((EndpointDataSource)dataSource)
-        {
-        }
-
-        // Exposed for tests. We need to accept a more specific type in the constructor for DI
-        // to work.
-        protected DynamicPageEndpointSelector(EndpointDataSource dataSource)
         {
             if (dataSource == null)
             {

src/Mvc/Mvc.RazorPages/src/Infrastructure/DynamicPageEndpointSelectorCache.cs

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+
+namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
+{
+    internal class DynamicPageEndpointSelectorCache
+    {
+        private readonly ConcurrentDictionary<int, EndpointDataSource> _dataSourceCache = new();
+        private readonly ConcurrentDictionary<int, DynamicPageEndpointSelector> _endpointSelectorCache = new();
+
+        public void AddDataSource(PageActionEndpointDataSource dataSource)
+        {
+            _dataSourceCache.GetOrAdd(dataSource.DataSourceId, dataSource);
+        }
+
+        // For testing purposes only
+        internal void AddDataSource(EndpointDataSource dataSource, int key) =>
+            _dataSourceCache.GetOrAdd(key, dataSource);
+
+        public DynamicPageEndpointSelector GetEndpointSelector(Endpoint endpoint)
+        {
+            if (endpoint?.Metadata == null)
+            {
+                return null;
+            }
+
+            var dataSourceId = endpoint.Metadata.GetMetadata<PageEndpointDataSourceIdMetadata>();
+            return _endpointSelectorCache.GetOrAdd(dataSourceId.Id, key => EnsureDataSource(key));
+        }
+
+        private DynamicPageEndpointSelector EnsureDataSource(int key)
+        {
+            if (!_dataSourceCache.TryGetValue(key, out var dataSource))
+            {
+                throw new InvalidOperationException($"Data source with key '{key}' not registered.");
+            }
+
+            return new DynamicPageEndpointSelector(dataSource);
+        }
+    }
+}

src/Mvc/Mvc.RazorPages/src/Infrastructure/PageActionEndpointDataSource.cs

@@ -18,11 +18,13 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         private readonly OrderedEndpointsSequenceProvider _orderSequence;
 
         public PageActionEndpointDataSource(
+            PageActionEndpointDataSourceIdProvider dataSourceIdProvider,
             IActionDescriptorCollectionProvider actions,
             ActionEndpointFactory endpointFactory,
             OrderedEndpointsSequenceProvider orderedEndpoints)
             : base(actions)
         {
+            DataSourceId = dataSourceIdProvider.CreateId();
             _endpointFactory = endpointFactory;
             _orderSequence = orderedEndpoints;
             DefaultBuilder = new PageActionEndpointConventionBuilder(Lock, Conventions);
@@ -32,6 +34,8 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
             Subscribe();
         }
 
+        public int DataSourceId { get; }
+
         public PageActionEndpointConventionBuilder DefaultBuilder { get; }
 
         // Used to control whether we create 'inert' (non-routable) endpoints for use in dynamic
@@ -53,12 +57,12 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
             return endpoints;
         }
 
-        internal void AddDynamicPageEndpoint(IEndpointRouteBuilder endpoints, string pattern, Type transformerType, object state)
+        internal void AddDynamicPageEndpoint(IEndpointRouteBuilder endpoints, string pattern, Type transformerType, object state, int? order = null)
         {
             CreateInertEndpoints = true;
             lock (Lock)
             {
-                var order = _orderSequence.GetNext();
+                order ??= _orderSequence.GetNext();
 
                 endpoints.Map(
                     pattern,
@@ -68,11 +72,11 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                     })
                     .Add(b =>
                     {
-                        ((RouteEndpointBuilder)b).Order = order;
+                        ((RouteEndpointBuilder)b).Order = order.Value;
                         b.Metadata.Add(new DynamicPageRouteValueTransformerMetadata(transformerType, state));
+                        b.Metadata.Add(new PageEndpointDataSourceIdMetadata(DataSourceId));
                     });
             }
         }
     }
 }
-

src/Mvc/Mvc.RazorPages/src/Infrastructure/PageActionEndpointDataSourceFactory.cs

@@ -0,0 +1,30 @@
+// 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 Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.AspNetCore.Mvc.Routing;
+
+namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
+{
+    internal class PageActionEndpointDataSourceFactory
+    {
+        private readonly PageActionEndpointDataSourceIdProvider _dataSourceIdProvider;
+        private readonly IActionDescriptorCollectionProvider _actions;
+        private readonly ActionEndpointFactory _endpointFactory;
+
+        public PageActionEndpointDataSourceFactory(
+            PageActionEndpointDataSourceIdProvider dataSourceIdProvider,
+            IActionDescriptorCollectionProvider actions,
+            ActionEndpointFactory endpointFactory)
+        {
+            _dataSourceIdProvider = dataSourceIdProvider;
+            _actions = actions;
+            _endpointFactory = endpointFactory;
+        }
+
+        public PageActionEndpointDataSource Create(OrderedEndpointsSequenceProvider orderProvider)
+        {
+            return new PageActionEndpointDataSource(_dataSourceIdProvider, _actions, _endpointFactory, orderProvider);
+        }
+    }
+}

src/Mvc/Mvc.RazorPages/src/Infrastructure/PageActionEndpointDataSourceIdProvider.cs

@@ -0,0 +1,17 @@
+// 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;
+
+namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
+{
+    internal class PageActionEndpointDataSourceIdProvider
+    {
+        private int _nextId = 1;
+
+        internal int CreateId()
+        {
+            return Interlocked.Increment(ref _nextId);
+        }
+    }
+}

src/Mvc/Mvc.RazorPages/src/Infrastructure/PageEndpointDataSourceIdMetadata.cs

@@ -0,0 +1,15 @@
+// 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.AspNetCore.Mvc.RazorPages.Infrastructure
+{
+    internal class PageEndpointDataSourceIdMetadata
+    {
+        public PageEndpointDataSourceIdMetadata(int id)
+        {
+            Id = id;
+        }
+
+        public int Id { get; }
+    }
+}

src/Mvc/Mvc.RazorPages/test/Infrastructure/DynamicPageEndpointMatcherPolicyTest.cs

@@ -51,12 +51,13 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                 new EndpointMetadataCollection(new object[]
                 {
                     new DynamicPageRouteValueTransformerMetadata(typeof(CustomTransformer), State),
+                    new PageEndpointDataSourceIdMetadata(1),
                 }),
                 "dynamic");
 
             DataSource = new DefaultEndpointDataSource(PageEndpoints);
 
-            Selector = new TestDynamicPageEndpointSelector(DataSource);
+            SelectorCache = new TestDynamicPageEndpointSelectorCache(DataSource);
 
             var services = new ServiceCollection();
             services.AddRouting();
@@ -106,7 +107,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
 
         private PageLoader Loader { get; }
 
-        private DynamicPageEndpointSelector Selector { get; }
+        private DynamicPageEndpointSelectorCache SelectorCache { get; }
 
         private object State { get; }
 
@@ -120,7 +121,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_NoMatch()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { null, };
@@ -150,7 +151,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_HasMatchNoEndpointFound()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { null, };
@@ -181,7 +182,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_HasMatchFindsEndpoint_WithoutRouteValues()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { null, };
@@ -221,7 +222,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_HasMatchFindsEndpoint_WithRouteValues()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -272,7 +273,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_Throws_ForTransformersWithInvalidLifetime()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -302,7 +303,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_CanDiscardFoundEndpoints()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -340,7 +341,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_CanReplaceFoundEndpoints()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -400,7 +401,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
         public async Task ApplyAsync_CanExpandTheListOfFoundEndpoints()
         {
             // Arrange
-            var policy = new DynamicPageEndpointMatcherPolicy(Selector, Loader, Comparer);
+            var policy = new DynamicPageEndpointMatcherPolicy(SelectorCache, Loader, Comparer);
 
             var endpoints = new[] { DynamicEndpoint, };
             var values = new RouteValueDictionary[] { new RouteValueDictionary(new { slug = "test", }), };
@@ -438,11 +439,11 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
             Assert.Same(LoadedEndpoints[1], candidates[1].Endpoint);
         }
 
-        private class TestDynamicPageEndpointSelector : DynamicPageEndpointSelector
+        private class TestDynamicPageEndpointSelectorCache : DynamicPageEndpointSelectorCache
         {
-            public TestDynamicPageEndpointSelector(EndpointDataSource dataSource)
+            public TestDynamicPageEndpointSelectorCache(EndpointDataSource dataSource)
-                : base(dataSource)
             {
+                AddDataSource(dataSource, 1);
             }
         }
 

src/Mvc/Mvc.RazorPages/test/Infrastructure/PageActionEndpointDataSourceTest.cs

@@ -92,7 +92,7 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
 
         private protected override ActionEndpointDataSourceBase CreateDataSource(IActionDescriptorCollectionProvider actions, ActionEndpointFactory endpointFactory)
         {
-            return new PageActionEndpointDataSource(actions, endpointFactory, new OrderedEndpointsSequenceProvider());
+            return new PageActionEndpointDataSource(new PageActionEndpointDataSourceIdProvider(), actions, endpointFactory, new OrderedEndpointsSequenceProvider());
         }
 
         protected override ActionDescriptor CreateActionDescriptor(

src/Mvc/benchmarks/Microsoft.AspNetCore.Mvc.Performance/ControllerActionEndpointDatasourceBenchmark.cs

@@ -109,6 +109,7 @@ namespace Microsoft.AspNetCore.Mvc.Performance
         private ControllerActionEndpointDataSource CreateDataSource(IActionDescriptorCollectionProvider actionDescriptorCollectionProvider)
         {
             var dataSource = new ControllerActionEndpointDataSource(
+                new ControllerActionEndpointDataSourceIdProvider(),
                 actionDescriptorCollectionProvider,
                 new ActionEndpointFactory(new MockRoutePatternTransformer()),
                 new OrderedEndpointsSequenceProvider());

src/Mvc/test/Mvc.FunctionalTests/RoutingAcrossPipelineBranchesTest.cs

@@ -0,0 +1,172 @@
+// 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.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Net.Http.Json;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Hosting;
+using Microsoft.AspNetCore.Mvc.Testing;
+using RoutingWebSite;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.FunctionalTests
+{
+    public class RoutingAcrossPipelineBranchesTests : IClassFixture<MvcTestFixture<RoutingWebSite.StartupRoutingDifferentBranches>>
+    {
+        public RoutingAcrossPipelineBranchesTests(MvcTestFixture<RoutingWebSite.StartupRoutingDifferentBranches> fixture)
+        {
+            Factory = fixture.Factories.FirstOrDefault() ?? fixture.WithWebHostBuilder(ConfigureWebHostBuilder);
+        }
+
+        private static void ConfigureWebHostBuilder(IWebHostBuilder builder) => builder.UseStartup<RoutingWebSite.StartupRoutingDifferentBranches>();
+
+        public WebApplicationFactory<StartupRoutingDifferentBranches> Factory { get; }
+
+        [Fact]
+        public async Task MatchesConventionalRoutesInTheirBranches()
+        {
+            var client = Factory.CreateClient();
+
+            // Arrange
+            var subdirRequest = new HttpRequestMessage(HttpMethod.Get, "subdir/literal/Branches/Index/s");
+            var commonRequest = new HttpRequestMessage(HttpMethod.Get, "common/Branches/Index/c/literal");
+            var defaultRequest = new HttpRequestMessage(HttpMethod.Get, "Branches/literal/Index/d");
+
+            // Act
+            var subdirResponse = await client.SendAsync(subdirRequest);
+            var subdirContent = await subdirResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            var commonResponse = await client.SendAsync(commonRequest);
+            var commonContent = await commonResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            var defaultResponse = await client.SendAsync(defaultRequest);
+            var defaultContent = await defaultResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, subdirResponse.StatusCode);
+            Assert.True(subdirContent.RouteValues.TryGetValue("subdir", out var subdir));
+            Assert.Equal("s", subdir);
+
+            Assert.Equal(HttpStatusCode.OK, commonResponse.StatusCode);
+            Assert.True(commonContent.RouteValues.TryGetValue("common", out var common));
+            Assert.Equal("c", common);
+
+            Assert.Equal(HttpStatusCode.OK, defaultResponse.StatusCode);
+            Assert.True(defaultContent.RouteValues.TryGetValue("default", out var @default));
+            Assert.Equal("d", @default);
+        }
+
+        [Fact]
+        public async Task LinkGenerationWorksOnEachBranch()
+        {
+            var client = Factory.CreateClient();
+            var linkQuery = "?link";
+
+                // Arrange
+            var subdirRequest = new HttpRequestMessage(HttpMethod.Get, "subdir/literal/Branches/Index/s" + linkQuery);
+            var commonRequest = new HttpRequestMessage(HttpMethod.Get, "common/Branches/Index/c/literal" + linkQuery);
+            var defaultRequest = new HttpRequestMessage(HttpMethod.Get, "Branches/literal/Index/d" + linkQuery);
+
+            // Act
+            var subdirResponse = await client.SendAsync(subdirRequest);
+            var subdirContent = await subdirResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            var commonResponse = await client.SendAsync(commonRequest);
+            var commonContent = await commonResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            var defaultResponse = await client.SendAsync(defaultRequest);
+            var defaultContent = await defaultResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, subdirResponse.StatusCode);
+            Assert.Equal("/subdir/literal/Branches/Index/s", subdirContent.Link);
+
+            Assert.Equal(HttpStatusCode.OK, commonResponse.StatusCode);
+            Assert.Equal("/common/Branches/Index/c/literal", commonContent.Link);
+
+            Assert.Equal(HttpStatusCode.OK, defaultResponse.StatusCode);
+            Assert.Equal("/Branches/literal/Index/d", defaultContent.Link);
+        }
+
+        // This still works because even though each middleware now gets its own data source,
+        // those data sources still get added to a global collection in IOptions<RouteOptions>>.DataSources
+        [Fact]
+        public async Task LinkGenerationStillWorksAcrossBranches()
+        {
+            var client = Factory.CreateClient();
+            var linkQuery = "?link";
+
+            // Arrange
+            var subdirRequest = new HttpRequestMessage(HttpMethod.Get, "subdir/literal/Branches/Index/s" + linkQuery + "&link_common=c&link_subdir");
+            var defaultRequest = new HttpRequestMessage(HttpMethod.Get, "Branches/literal/Index/d" + linkQuery + "&link_subdir=s");
+
+            // Act
+            var subdirResponse = await client.SendAsync(subdirRequest);
+            var subdirContent = await subdirResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            var defaultResponse = await client.SendAsync(defaultRequest);
+            var defaultContent = await defaultResponse.Content.ReadFromJsonAsync<RouteInfo>();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, subdirResponse.StatusCode);
+            // Note that this link and the one below don't account for the path base being in a different branch.
+            // The recommendation for customers doing link generation across branches will be to always generate absolute
+            // URIs by explicitly passing the path base to the link generator.
+            // In the future there are improvements we might be able to do in most common cases to lift this limitation if we receive
+            // feedback about it.
+            Assert.Equal("/subdir/Branches/Index/c/literal", subdirContent.Link);
+
+            Assert.Equal(HttpStatusCode.OK, defaultResponse.StatusCode);
+            Assert.Equal("/literal/Branches/Index/s", defaultContent.Link);
+        }
+
+        [Fact]
+        public async Task DoesNotMatchConventionalRoutesDefinedInOtherBranches()
+        {
+            var client = Factory.CreateClient();
+
+            // Arrange
+            var commonRequest = new HttpRequestMessage(HttpMethod.Get, "common/literal/Branches/Index/s");
+            var subdirRequest = new HttpRequestMessage(HttpMethod.Get, "subdir/Branches/Index/c/literal");
+            var defaultRequest = new HttpRequestMessage(HttpMethod.Get, "common/Branches/literal/Index/d");
+
+            // Act
+            var commonResponse = await client.SendAsync(commonRequest);
+
+            var subdirResponse = await client.SendAsync(subdirRequest);
+
+            var defaultResponse = await client.SendAsync(defaultRequest);
+
+            // Assert
+            Assert.Equal(HttpStatusCode.NotFound, commonResponse.StatusCode);
+            Assert.Equal(HttpStatusCode.NotFound, subdirResponse.StatusCode);
+            Assert.Equal(HttpStatusCode.NotFound, defaultResponse.StatusCode);
+        }
+
+        [Fact]
+        public async Task ConventionalAndDynamicRouteOrdersAreScopedPerBranch()
+        {
+            var client = Factory.CreateClient();
+
+            // Arrange
+            var request = new HttpRequestMessage(HttpMethod.Get, "dynamicattributeorder/dynamic/route/rest");
+
+            // Act
+            var response = await client.SendAsync(request);
+            var content = await response.Content.ReadFromJsonAsync<RouteInfo>();
+
+            // Assert
+            Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+            Assert.True(content.RouteValues.TryGetValue("action", out var action));
+
+            // The dynamic route wins because it has Order 1 (scope to that router) and
+            // has higher precedence.
+            Assert.Equal("Index", action);
+        }
+
+        private record RouteInfo(string RouteName, IDictionary<string, string> RouteValues, string Link);
+    }
+}

src/Mvc/test/WebSites/Common/TestResponseGenerator.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;

src/Mvc/test/WebSites/RoutingWebSite/Controllers/BranchesController.cs

@@ -0,0 +1,29 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Mvc.RoutingWebSite.Controllers
+{
+    public class BranchesController : Controller
+    {
+        private readonly TestResponseGenerator _generator;
+
+        public BranchesController(TestResponseGenerator generator)
+        {
+            _generator = generator;
+        }
+
+        public IActionResult Index()
+        {
+            return _generator.Generate();
+        }
+
+        [HttpGet("dynamicattributeorder/{some}/{value}/{**slug}", Order = 1)]
+        public IActionResult Attribute()
+        {
+            return _generator.Generate();
+        }
+    }
+}

src/Mvc/test/WebSites/RoutingWebSite/Program.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.IO;

src/Mvc/test/WebSites/RoutingWebSite/StartupForDynamic.cs

@@ -7,6 +7,7 @@ using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Routing;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.Extensions.DependencyInjection;
@@ -24,6 +25,8 @@ namespace RoutingWebSite
                 .SetCompatibilityVersion(CompatibilityVersion.Latest);
 
             services.AddTransient<Transformer>();
+            services.AddScoped<TestResponseGenerator>();
+            services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();
 
             // Used by some controllers defined in this project.
             services.Configure<RouteOptions>(options => options.ConstraintMap["slugify"] = typeof(SlugifyParameterTransformer));

src/Mvc/test/WebSites/RoutingWebSite/StartupRoutingDifferentBranches.cs

@@ -0,0 +1,104 @@
+// 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.Tasks;
+using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.ApplicationModels;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
+using Microsoft.AspNetCore.Mvc.Routing;
+using Microsoft.AspNetCore.Routing;
+using Microsoft.Extensions.DependencyInjection;
+
+namespace RoutingWebSite
+{
+    public class StartupRoutingDifferentBranches
+    {
+        // Set up application services
+        public void ConfigureServices(IServiceCollection services)
+        {
+            var pageRouteTransformerConvention = new PageRouteTransformerConvention(new SlugifyParameterTransformer());
+
+            services
+                .AddMvc(ConfigureMvcOptions)
+                .AddNewtonsoftJson()
+                .AddRazorPagesOptions(options =>
+                {
+                    options.Conventions.AddPageRoute("/PageRouteTransformer/PageWithConfiguredRoute", "/PageRouteTransformer/NewConventionRoute/{id?}");
+                    options.Conventions.AddFolderRouteModelConvention("/PageRouteTransformer", model =>
+                    {
+                        pageRouteTransformerConvention.Apply(model);
+                    });
+                })
+                .SetCompatibilityVersion(CompatibilityVersion.Latest);
+
+            ConfigureRoutingServices(services);
+
+            services.AddScoped<TestResponseGenerator>();
+            // This is used by test response generator
+            services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();
+            services.AddSingleton<BranchesTransformer>();
+        }
+
+        public virtual void Configure(IApplicationBuilder app)
+        {
+            app.Map("/subdir", branch =>
+            {
+                branch.UseRouting();
+
+                branch.UseEndpoints(endpoints =>
+                {
+                    endpoints.MapRazorPages();
+                    endpoints.MapControllerRoute(null, "literal/{controller}/{action}/{subdir}");
+                    endpoints.MapDynamicControllerRoute<BranchesTransformer>("literal/dynamic/controller/{**slug}");
+                });
+            });
+
+            app.Map("/common", branch =>
+            {
+                branch.UseRouting();
+
+                branch.UseEndpoints(endpoints =>
+                {
+                    endpoints.MapControllerRoute(null, "{controller}/{action}/{common}/literal");
+                    endpoints.MapDynamicControllerRoute<BranchesTransformer>("dynamic/controller/literal/{**slug}");
+                });
+            });
+
+            app.UseRouting();
+            app.UseEndpoints(endpoints =>
+            {
+                endpoints.MapControllers();
+                endpoints.MapDynamicControllerRoute<BranchesTransformer>("dynamicattributeorder/dynamic/route/{**slug}");
+                endpoints.MapControllerRoute(null, "{controller}/literal/{action}/{default}");
+            });
+
+            app.Run(c =>
+            {
+                return c.Response.WriteAsync("Hello from middleware after routing");
+            });
+        }
+
+        protected virtual void ConfigureMvcOptions(MvcOptions options)
+        {
+            // Add route token transformer to one controller
+            options.Conventions.Add(new ControllerRouteTokenTransformerConvention(
+                typeof(ParameterTransformerController),
+                new SlugifyParameterTransformer()));
+        }
+
+        protected virtual void ConfigureRoutingServices(IServiceCollection services)
+        {
+            services.AddRouting(options => options.ConstraintMap["slugify"] = typeof(SlugifyParameterTransformer));
+        }
+    }
+
+    public class BranchesTransformer : DynamicRouteValueTransformer
+    {
+        public override ValueTask<RouteValueDictionary> TransformAsync(HttpContext httpContext, RouteValueDictionary values)
+        {
+            return new ValueTask<RouteValueDictionary>(new RouteValueDictionary(new { controller = "Branches", action = "Index" }));
+        }
+    }
+}