Remove fast-path closures from EventBasedLRUCache (#2170)

Author: stephentoub

src/Microsoft.IdentityModel.Tokens/EventBasedLRUCache.cs

@@ -390,10 +390,12 @@ public bool SetValue(TKey key, TValue value, DateTime expirationTime)
                 cacheItem.ExpirationTime = expirationTime;
                 if (_maintainLRU)
                 {
+                    var localCacheItem = cacheItem; // avoid closure when !_maintainLRU
+                    var localThis = this;
                     AddActionToEventQueue(() =>
                     {
-                        _doubleLinkedList.Remove(cacheItem);
-                        _doubleLinkedList.AddFirst(cacheItem);
+                        localThis._doubleLinkedList.Remove(localCacheItem);
+                        localThis._doubleLinkedList.AddFirst(localCacheItem);
                     });
                 }
             }
@@ -416,11 +418,13 @@ public bool SetValue(TKey key, TValue value, DateTime expirationTime)
                 // add the new node to the _doubleLinkedList if _maintainLRU == true
                 if (_maintainLRU)
                 {
+                    var localNewCacheItem = newCacheItem; // avoid closure when !_maintainLRU
+                    var localThis = this;
                     AddActionToEventQueue(() =>
                     {
                         // Add a remove operation in case two threads are trying to add the same value. Only the second remove will succeed in this case.
-                        _doubleLinkedList.Remove(newCacheItem);
-                        _doubleLinkedList.AddFirst(newCacheItem);
+                        localThis._doubleLinkedList.Remove(localNewCacheItem);
+                        localThis._doubleLinkedList.AddFirst(localNewCacheItem);
                     });
                 }
 
@@ -492,10 +496,12 @@ public bool TryGetValue(TKey key, out TValue value)
             // make sure node hasn't been removed by a different thread
             if (_maintainLRU)
             {
+                var localCacheItem = cacheItem; // avoid closure on fast path or when !_maintainLRU
+                var localThis = this;
                 AddActionToEventQueue(() =>
                 {
-                    _doubleLinkedList.Remove(cacheItem);
-                    _doubleLinkedList.AddFirst(cacheItem);
+                    localThis._doubleLinkedList.Remove(localCacheItem);
+                    localThis._doubleLinkedList.AddFirst(localCacheItem);
                 });
             }
 
@@ -516,7 +522,11 @@ public bool TryRemove(TKey key, out TValue value)
             }
 
             if (_maintainLRU)
-                AddActionToEventQueue(() => _doubleLinkedList.Remove(cacheItem));
+            {
+                var localCacheItem = cacheItem; // avoid closure on fast path or when !_maintainLRU
+                var localThis = this;
+                AddActionToEventQueue(() => localThis._doubleLinkedList.Remove(localCacheItem));
+            }
 
             value = cacheItem.Value;
             OnItemRemoved?.Invoke(cacheItem.Value);