U4-4931 - also for ObjectCacheRuntime provider

Conflicts:
	src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs

src/Umbraco.Core/Cache/ObjectCacheRuntimeCacheProvider.cs

@@ -19,11 +19,29 @@ namespace Umbraco.Core.Cache
         private readonly ReaderWriterLockSlim _locker = new ReaderWriterLockSlim(LockRecursionPolicy.SupportsRecursion);
         internal ObjectCache MemoryCache;
 
+        // an object that represent a value that has not been created yet
+        protected readonly object ValueNotCreated = new object();
+
         public ObjectCacheRuntimeCacheProvider()
         {
             MemoryCache = new MemoryCache("in-memory");
         }
 
+        protected object GetSafeLazyValue(Lazy<object> lazy, bool onlyIfValueIsCreated = false)
+        {
+            try
+            {
+                // if onlyIfValueIsCreated, do not trigger value creation
+                // must return something, though, to differenciate from null values
+                if (onlyIfValueIsCreated && lazy.IsValueCreated == false) return ValueNotCreated;
+                return lazy.Value;
+            }
+            catch
+            {
+                return null;
+            }
+        }
+
         #region Clear
 
         public virtual void ClearAllCache()
@@ -53,7 +71,8 @@ namespace Umbraco.Core.Cache
                     {
                         // x.Value is Lazy<object> and not null, its value may be null
                         // remove null values as well, does not hurt
-                        var value = ((Lazy<object>) x.Value).Value;
+                        // get non-created as NonCreatedValue & exceptions as null
+                        var value = GetSafeLazyValue((Lazy<object>)x.Value, true);
                         return value == null || value.GetType().ToString().InvariantEquals(typeName);
                     })
                     .Select(x => x.Key)
@@ -72,7 +91,8 @@ namespace Umbraco.Core.Cache
                     {
                         // x.Value is Lazy<object> and not null, its value may be null
                         // remove null values as well, does not hurt
-                        var value = ((Lazy<object>)x.Value).Value;
+                        // get non-created as NonCreatedValue & exceptions as null
+                        var value = GetSafeLazyValue((Lazy<object>)x.Value, true);
                         return value == null || value.GetType() == typeOfT;
                     })
                     .Select(x => x.Key)
@@ -91,7 +111,8 @@ namespace Umbraco.Core.Cache
                     {
                         // x.Value is Lazy<object> and not null, its value may be null
                         // remove null values as well, does not hurt
-                        var value = ((Lazy<object>)x.Value).Value;
+                        // get non-created as NonCreatedValue & exceptions as null
+                        var value = GetSafeLazyValue((Lazy<object>)x.Value, true);
                         if (value == null) return true;
                         return value.GetType() == typeOfT
                             && predicate(x.Key, (T) value);
@@ -132,35 +153,42 @@ namespace Umbraco.Core.Cache
 
         public IEnumerable<object> GetCacheItemsByKeySearch(string keyStartsWith)
         {
+            KeyValuePair<string, object>[] entries;
             using (new ReadLock(_locker))
             {
-                return MemoryCache
+                entries = MemoryCache
                     .Where(x => x.Key.InvariantStartsWith(keyStartsWith))
-                    .Select(x => ((Lazy<object>) x.Value).Value)
-                    .Where(x => x != null) // backward compat, don't store null values in the cache
-                    .ToList();
+                    .ToArray(); // evaluate while locked
             }
+            return entries
+                .Select(x => GetSafeLazyValue((Lazy<object>)x.Value)) // return exceptions as null
+                .Where(x => x != null) // backward compat, don't store null values in the cache
+                .ToList();
         }
 
         public IEnumerable<object> GetCacheItemsByKeyExpression(string regexString)
         {
+            KeyValuePair<string, object>[] entries;
             using (new ReadLock(_locker))
             {
-                return MemoryCache
+                entries = MemoryCache
                     .Where(x => Regex.IsMatch(x.Key, regexString))
-                    .Select(x => ((Lazy<object>) x.Value).Value)
-                    .Where(x => x != null) // backward compat, don't store null values in the cache
-                    .ToList();
+                    .ToArray(); // evaluate while locked
             }
+            return entries
+                .Select(x => GetSafeLazyValue((Lazy<object>)x.Value)) // return exceptions as null
+                .Where(x => x != null) // backward compat, don't store null values in the cache
+                .ToList();
         }
 
         public object GetCacheItem(string cacheKey)
         {
+            Lazy<object> result;
             using (new ReadLock(_locker))
             {
-                var result = MemoryCache.Get(cacheKey) as Lazy<object>;
-                return result == null ? null : result.Value;
+                result = MemoryCache.Get(cacheKey) as Lazy<object>; // null if key not found
             }
+            return result == null ? null : GetSafeLazyValue(result); // return exceptions as null
         }
 
         public object GetCacheItem(string cacheKey, Func<object> getCacheItem)
@@ -177,12 +205,12 @@ namespace Umbraco.Core.Cache
             using (var lck = new UpgradeableReadLock(_locker))
             {
                 result = MemoryCache.Get(cacheKey) as Lazy<object>;
-                if (result == null || (result.IsValueCreated && result.Value == null))
+                if (result == null || GetSafeLazyValue(result, true) == null) // get non-created as NonCreatedValue & exceptions as null
                 {
-                    lck.UpgradeToWriteLock();
-
                     result = new Lazy<object>(getCacheItem);
                     var policy = GetPolicy(timeout, isSliding, removedCallback, dependentFiles);
+
+                    lck.UpgradeToWriteLock();
                     MemoryCache.Set(cacheKey, result, policy);
                 }
             }