Fix caching paging during read.

pkg/analysis_server/lib/src/index/page_node_manager.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library index.page_node_manager;
 
 import 'dart:collection';
 import 'dart:typed_data';
 
+import 'package:analysis_server/src/index/b_plus_tree.dart';
 import 'package:analysis_server/src/index/lru_cache.dart';
 
-import 'b_plus_tree.dart';
-
 
 /**
  * A [NodeManager] that caches a specified number of index and leaf nodes.
  */
 class CachingNodeManager<K, V, N> implements NodeManager<K, V, N> {
   final NodeManager<K, V, N> _delegate;
   LRUCache<N, IndexNodeData<K, N>> _indexCache;
   LRUCache<N, LeafNodeData<K, V>> _leafCache;
 
   CachingNodeManager(this._delegate, int indexNodeCacheSize,
@@ skipping 28 matching lines @@
   }
 
   @override
   bool isIndex(N id) {
     return _delegate.isIndex(id);
   }
 
   @override
   IndexNodeData<K, N> readIndex(N id) {
     IndexNodeData<K, N> data = _indexCache.get(id);
-    if (data != null) {
-      return data;
+    if (data == null) {
+      data = _delegate.readIndex(id);
+      _indexCache.put(id, data);
     }
-    return _delegate.readIndex(id);
+    return data;
   }
 
   @override
   LeafNodeData<K, V> readLeaf(N id) {
     LeafNodeData<K, V> data = _leafCache.get(id);
-    if (data != null) {
-      return data;
+    if (data == null) {
+      data = _delegate.readLeaf(id);
+      _leafCache.put(id, data);
     }
-    return _delegate.readLeaf(id);
+    return data;
   }
 
   @override
   void writeIndex(N id, IndexNodeData<K, N> data) {
     _indexCache.put(id, data);
   }
 
   @override
   void writeLeaf(N id, LeafNodeData<K, V> data) {
     _leafCache.put(id, data);
@@ skipping 366 matching lines @@
   @override
   int decode(ByteData buffer) {
     return buffer.getUint32(0);
   }
 
   @override
   void encode(ByteData buffer, int element) {
     buffer.setUint32(0, element);
   }
 }