Make SecureConversation inner channel factory share the same HttpClie…

…nt as outer factory (#4438)

* Make SecureConversation inner channel factory share the same HttpClient as outer factory

* Fix lock semantics ref counting in mrucache

Co-authored-by: Matt Connew <matt.connew@microsoft.com>

src/System.Private.ServiceModel/src/Internals/System/Runtime/MruCache.cs

@@ -2,7 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-
 using System.Collections.Generic;
 using System.ServiceModel;
 
@@ -17,12 +16,29 @@ internal class MruCache<TKey, TValue> : IDisposable
         private readonly int _lowWatermark;
         private readonly int _highWatermark;
         private CacheEntry _mruEntry;
+        private int _refCount = 1;
+        private object _mutex = new object();
 
         public MruCache(int watermark)
             : this(watermark * 4 / 5, watermark)
         {
         }
 
+        // Returns whether the cache can be used by the caller after calling AddRef
+        public bool AddRef()
+        {
+            lock(_mutex)
+            {
+                if (_refCount == 0)
+                {
+                    return false;
+                }
+
+                _refCount++;
+                return true;
+            }
+        }
+
         //
         // The cache will grow until the high watermark. At which point, the least recently used items
         // will be purge until the cache's size is reduced to low watermark
@@ -202,17 +218,29 @@ public bool TryGetValue(TKey key, out TValue value)
 
         public void Dispose()
         {
-            Dispose(true);
+            int refCount;
+            lock (_mutex)
+            {
+                refCount = --_refCount;
+            }
+            Fx.Assert(refCount >= 0, "Ref count shouldn't go below zero");
+            if (refCount == 0)
+            {
+                Dispose(true);
+            }
         }
 
         protected virtual void Dispose(bool disposing)
         {
             if (disposing)
             {
-                if (!IsDisposed)
+                lock (_mutex)
                 {
-                    IsDisposed = true;
-                    Clear(true);
+                    if (!IsDisposed)
+                    {
+                        IsDisposed = true;
+                        Clear(true);
+                    }
                 }
             }
         }

src/System.Private.ServiceModel/src/System/ServiceModel/Channels/HttpChannelFactory.cs

@@ -131,6 +131,7 @@ internal HttpChannelFactory(HttpTransportBindingElement bindingElement, BindingC
             WebSocketSettings = WebSocketHelper.GetRuntimeWebSocketSettings(bindingElement.WebSocketSettings);
             _clientWebSocketFactory = ClientWebSocketFactory.GetFactory();
             _webSocketSoapContentType = new Lazy<string>(() => MessageEncoderFactory.CreateSessionEncoder().ContentType, LazyThreadSafetyMode.ExecutionAndPublication);
+            _httpClientCache = bindingElement.GetProperty<MruCache<string, HttpClient>>(context);
         }
 
         public bool AllowCookies { get; }
@@ -255,17 +256,6 @@ internal async Task<HttpClient> GetHttpClientAsync(EndpointAddress to, Uri via,
             NetworkCredential credential = await HttpChannelUtilities.GetCredentialAsync(AuthenticationScheme,
                 tokenProvider, impersonationLevelWrapper, authenticationLevelWrapper, timeout);
 
-            if (_httpClientCache == null)
-            {
-                lock (ThisLock)
-                {
-                    if (_httpClientCache == null)
-                    {
-                        _httpClientCache = new MruCache<string, HttpClient>(10);
-                    }
-                }
-            }
-
             HttpClient httpClient;
 
             string connectionGroupName = GetConnectionGroupName(credential, authenticationLevelWrapper.Value,

src/System.Private.ServiceModel/src/System/ServiceModel/Channels/HttpTransportBindingElement.cs

@@ -6,6 +6,7 @@
 using System.ComponentModel;
 using System.Diagnostics.Contracts;
 using System.Net;
+using System.Net.Http;
 using System.Net.Security;
 using System.Runtime;
 using System.Security.Authentication.ExtendedProtection;
@@ -29,6 +30,7 @@ public class HttpTransportBindingElement
         private WebSocketTransportSettings _webSocketSettings;
         private ExtendedProtectionPolicy _extendedProtectionPolicy;
         private int _maxPendingAccepts;
+        private MruCache<string, HttpClient> _httpClientCache;
 
         public HttpTransportBindingElement()
             : base()
@@ -395,6 +397,11 @@ public override T GetProperty<T>(BindingContext context)
             {
                 return (T)(object)new TransportCompressionSupportHelper();
             }
+            else if (typeof(T) == typeof(MruCache<string, HttpClient>))
+            {
+                EnsureHttpClientCache();
+                return (T)(object)_httpClientCache;
+            }
             else
             {
                 Contract.Assert(context.BindingParameters != null);
@@ -406,6 +413,16 @@ public override T GetProperty<T>(BindingContext context)
             }
         }
 
+        private MruCache<string, HttpClient> EnsureHttpClientCache()
+        {
+            if (_httpClientCache == null || !_httpClientCache.AddRef())
+            {
+                _httpClientCache = new MruCache<string, HttpClient>(10);
+            }
+
+            return _httpClientCache;
+        }
+
         public override bool CanBuildChannelFactory<TChannel>(BindingContext context)
         {
             if (typeof(TChannel) == typeof(IRequestChannel))