NuCache: reorg some classes

src/Umbraco.Web/PublishedCache/NuCache/Snap/GenObj.cs

@@ -0,0 +1,37 @@
+using System;
+using System.Threading;
+
+namespace Umbraco.Web.PublishedCache.NuCache.Snap
+{
+    internal class GenObj
+    {
+        public GenObj(long gen)
+        {
+            Gen = gen;
+            WeakGenRef = new WeakReference(null);
+        }
+
+        public GenRef GetGenRef()
+        {
+            // not thread-safe but always invoked from within a lock
+            var genRef = (GenRef)WeakGenRef.Target;
+            if (genRef == null)
+                WeakGenRef.Target = genRef = new GenRef(this);
+            return genRef;
+        }
+
+        public readonly long Gen;
+        public readonly WeakReference WeakGenRef;
+        public int Count;
+
+        public void Reference()
+        {
+            Interlocked.Increment(ref Count);
+        }
+
+        public void Release()
+        {
+            Interlocked.Decrement(ref Count);
+        }
+    }
+}

src/Umbraco.Web/PublishedCache/NuCache/Snap/GenRef.cs

@@ -0,0 +1,13 @@
+namespace Umbraco.Web.PublishedCache.NuCache.Snap
+{
+    internal class GenRef
+    {
+        public GenRef(GenObj genObj)
+        {
+            GenObj = genObj;
+        }
+
+        public readonly GenObj GenObj;
+        public long Gen => GenObj.Gen;
+    }
+}

src/Umbraco.Web/PublishedCache/NuCache/Snap/LinkedNode.cs

@@ -0,0 +1,20 @@
+namespace Umbraco.Web.PublishedCache.NuCache.Snap
+{
+    internal class LinkedNode<TValue>
+        where TValue : class
+    {
+        public LinkedNode(TValue value, long gen, LinkedNode<TValue> next = null)
+        {
+            Value = value;
+            Gen = gen;
+            Next = next;
+        }
+
+        public readonly long Gen;
+
+        // reading & writing references is thread-safe on all .NET platforms
+        // mark as volatile to ensure we always read the correct value
+        public volatile TValue Value;
+        public volatile LinkedNode<TValue> Next;
+    }
+}