From 7ed6c0c1a2bd75c10e7d90e858ae7ac426f1ff66 Mon Sep 17 00:00:00 2001
From: Steve Megson <steve@megson.org>
Date: Sun, 24 Nov 2019 13:44:09 +0000
Subject: [PATCH 1/2] Thread safety in EnsureApplicationUrl

---
 src/Umbraco.Core/RuntimeState.cs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/Umbraco.Core/RuntimeState.cs b/src/Umbraco.Core/RuntimeState.cs
index 5d34fe70a1..65c93ece05 100644
--- a/src/Umbraco.Core/RuntimeState.cs
+++ b/src/Umbraco.Core/RuntimeState.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Threading;
 using System.Web;
@@ -22,7 +23,7 @@ namespace Umbraco.Core
         private readonly ILogger _logger;
         private readonly IUmbracoSettingsSection _settings;
         private readonly IGlobalSettings _globalSettings;
-        private readonly HashSet<string> _applicationUrls = new HashSet<string>();
+        private readonly ConcurrentDictionary<string, byte> _applicationUrls = new ConcurrentDictionary<string, byte>();
         private readonly Lazy<IMainDom> _mainDom;
         private readonly Lazy<IServerRegistrar> _serverRegistrar;
 
@@ -106,11 +107,11 @@ namespace Umbraco.Core
             // (this is a simplified version of what was in 7.x)
             // note: should this be optional? is it expensive?
             var url = request == null ? null : ApplicationUrlHelper.GetApplicationUrlFromCurrentRequest(request, _globalSettings);
-            var change = url != null && !_applicationUrls.Contains(url);
+            var change = url != null && !_applicationUrls.ContainsKey(url);
             if (change)
             {
                 _logger.Info(typeof(ApplicationUrlHelper), "New url {Url} detected, re-discovering application url.", url);
-                _applicationUrls.Add(url);
+                _applicationUrls[url] = 0;
             }
 
             if (ApplicationUrl != null && !change) return;

From 311e2afde08131b592ea8dbe5c15514ba969ce47 Mon Sep 17 00:00:00 2001
From: Steve Megson <steve@megson.org>
Date: Tue, 26 Nov 2019 08:51:48 +0000
Subject: [PATCH 2/2] Use ConcurrentHashSet

---
 .../Collections/ConcurrentHashSet.cs          | 38 +++++++++++++++----
 src/Umbraco.Core/RuntimeState.cs              |  9 ++---
 2 files changed, 35 insertions(+), 12 deletions(-)

diff --git a/src/Umbraco.Core/Collections/ConcurrentHashSet.cs b/src/Umbraco.Core/Collections/ConcurrentHashSet.cs
index 54367ed588..c4dba51acd 100644
--- a/src/Umbraco.Core/Collections/ConcurrentHashSet.cs
+++ b/src/Umbraco.Core/Collections/ConcurrentHashSet.cs
@@ -70,7 +70,23 @@ namespace Umbraco.Core.Collections
         /// The number of elements contained in the <see cref="T:System.Collections.ICollection"/>.
         /// </returns>
         /// <filterpriority>2</filterpriority>
-        public int Count => GetThreadSafeClone().Count;
+        public int Count
+        {
+            get
+            {
+                try
+                {
+                    _instanceLocker.EnterReadLock();
+                    return _innerSet.Count;
+                }
+                finally
+                {
+                    if (_instanceLocker.IsReadLockHeld)
+                        _instanceLocker.ExitReadLock();
+                }
+
+            }
+        }
 
         /// <summary>
         /// Gets a value indicating whether the <see cref="T:System.Collections.Generic.ICollection`1"/> is read-only.
@@ -105,8 +121,7 @@ namespace Umbraco.Core.Collections
         /// <returns></returns>
         public bool TryAdd(T item)
         {
-            var clone = GetThreadSafeClone();
-            if (clone.Contains(item)) return false;
+            if (Contains(item)) return false;
             try
             {
                 _instanceLocker.EnterWriteLock();
@@ -150,7 +165,16 @@ namespace Umbraco.Core.Collections
         /// <param name="item">The object to locate in the <see cref="T:System.Collections.Generic.ICollection`1"/>.</param>
         public bool Contains(T item)
         {
-            return GetThreadSafeClone().Contains(item);
+            try
+            {
+                _instanceLocker.EnterReadLock();
+                return _innerSet.Contains(item);
+            }
+            finally
+            {
+                if (_instanceLocker.IsReadLockHeld)
+                    _instanceLocker.ExitReadLock();
+            }
         }
 
         /// <summary>
@@ -168,13 +192,13 @@ namespace Umbraco.Core.Collections
             HashSet<T> clone = null;
             try
             {
-                _instanceLocker.EnterWriteLock();
+                _instanceLocker.EnterReadLock();
                 clone = new HashSet<T>(_innerSet, _innerSet.Comparer);
             }
             finally
             {
-                if (_instanceLocker.IsWriteLockHeld)
-                    _instanceLocker.ExitWriteLock();
+                if (_instanceLocker.IsReadLockHeld)
+                    _instanceLocker.ExitReadLock();
             }
             return clone;
         }
diff --git a/src/Umbraco.Core/RuntimeState.cs b/src/Umbraco.Core/RuntimeState.cs
index 65c93ece05..74ec70828b 100644
--- a/src/Umbraco.Core/RuntimeState.cs
+++ b/src/Umbraco.Core/RuntimeState.cs
@@ -1,9 +1,8 @@
 using System;
-using System.Collections.Concurrent;
-using System.Collections.Generic;
 using System.Threading;
 using System.Web;
 using Semver;
+using Umbraco.Core.Collections;
 using Umbraco.Core.Configuration;
 using Umbraco.Core.Configuration.UmbracoSettings;
 using Umbraco.Core.Exceptions;
@@ -23,7 +22,7 @@ namespace Umbraco.Core
         private readonly ILogger _logger;
         private readonly IUmbracoSettingsSection _settings;
         private readonly IGlobalSettings _globalSettings;
-        private readonly ConcurrentDictionary<string, byte> _applicationUrls = new ConcurrentDictionary<string, byte>();
+        private readonly ConcurrentHashSet<string> _applicationUrls = new ConcurrentHashSet<string>();
         private readonly Lazy<IMainDom> _mainDom;
         private readonly Lazy<IServerRegistrar> _serverRegistrar;
 
@@ -107,11 +106,11 @@ namespace Umbraco.Core
             // (this is a simplified version of what was in 7.x)
             // note: should this be optional? is it expensive?
             var url = request == null ? null : ApplicationUrlHelper.GetApplicationUrlFromCurrentRequest(request, _globalSettings);
-            var change = url != null && !_applicationUrls.ContainsKey(url);
+            var change = url != null && !_applicationUrls.Contains(url);
             if (change)
             {
                 _logger.Info(typeof(ApplicationUrlHelper), "New url {Url} detected, re-discovering application url.", url);
-                _applicationUrls[url] = 0;
+                _applicationUrls.Add(url);
             }
 
             if (ApplicationUrl != null && !change) return;