Great AppCaches renaming

src/Umbraco.Core/Cache/HttpRequestAppCache.cs

@@ -0,0 +1,138 @@
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Web;
+
+namespace Umbraco.Core.Cache
+{
+    /// <summary>
+    /// Implements a fast <see cref="IAppCache"/> on top of HttpContext.Items.
+    /// </summary>
+    /// <remarks>
+    /// <para>If no current HttpContext items can be found (no current HttpContext,
+    /// or no Items...) then this cache acts as a pass-through and does not cache
+    /// anything.</para>
+    /// </remarks>
+    internal class HttpRequestAppCache : FastDictionaryAppCacheBase
+    {
+        private readonly HttpContextBase _context;
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="HttpRequestAppCache"/> class with a context, for unit tests!
+        /// </summary>
+        public HttpRequestAppCache(HttpContextBase context)
+        {
+            _context = context;
+        }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="HttpRequestAppCache"/> class.
+        /// </summary>
+        /// <remarks>
+        /// <para>Will use HttpContext.Current.</para>
+        /// fixme - should use IHttpContextAccessor
+        /// </remarks>
+        public HttpRequestAppCache()
+        { }
+
+        private IDictionary ContextItems => _context?.Items ?? HttpContext.Current?.Items;
+
+        private bool HasContextItems => _context?.Items != null || HttpContext.Current != null;
+
+        /// <inheritdoc />
+        public override object Get(string key, Func<object> factory)
+        {
+            //no place to cache so just return the callback result
+            if (HasContextItems == false) return factory();
+
+            key = GetCacheKey(key);
+
+            Lazy<object> result;
+
+            try
+            {
+                EnterWriteLock();
+                result = ContextItems[key] as Lazy<object>; // null if key not found
+
+                // cannot create value within the lock, so if result.IsValueCreated is false, just
+                // do nothing here - means that if creation throws, a race condition could cause
+                // more than one thread to reach the return statement below and throw - accepted.
+
+                if (result == null || GetSafeLazyValue(result, true) == null) // get non-created as NonCreatedValue & exceptions as null
+                {
+                    result = GetSafeLazy(factory);
+                    ContextItems[key] = result;
+                }
+            }
+            finally
+            {
+                ExitWriteLock();
+            }
+
+            // using GetSafeLazy and GetSafeLazyValue ensures that we don't cache
+            // exceptions (but try again and again) and silently eat them - however at
+            // some point we have to report them - so need to re-throw here
+
+            // this does not throw anymore
+            //return result.Value;
+
+            var value = result.Value; // will not throw (safe lazy)
+            if (value is ExceptionHolder eh) eh.Exception.Throw(); // throw once!
+            return value;
+        }
+
+        #region Entries
+
+        protected override IEnumerable<DictionaryEntry> GetDictionaryEntries()
+        {
+            const string prefix = CacheItemPrefix + "-";
+
+            if (HasContextItems == false) return Enumerable.Empty<DictionaryEntry>();
+
+            return ContextItems.Cast<DictionaryEntry>()
+                .Where(x => x.Key is string s && s.StartsWith(prefix));
+        }
+
+        protected override void RemoveEntry(string key)
+        {
+            if (HasContextItems == false) return;
+
+            ContextItems.Remove(key);
+        }
+
+        protected override object GetEntry(string key)
+        {
+            return HasContextItems ? ContextItems[key] : null;
+        }
+
+        #endregion
+
+        #region Lock
+
+        private bool _entered;
+
+        protected override void EnterReadLock() => EnterWriteLock();
+
+        protected override void EnterWriteLock()
+        {
+            if (HasContextItems)
+            {
+                System.Threading.Monitor.Enter(ContextItems.SyncRoot, ref _entered);
+            }
+        }
+
+        protected override void ExitReadLock() => ExitWriteLock();
+
+        protected override void ExitWriteLock()
+        {
+            if (_entered)
+            {
+                _entered = false;
+                System.Threading.Monitor.Exit(ContextItems.SyncRoot);
+            }
+        }
+
+        #endregion
+    }
+}