Github user satishd commented on a diff in the pull request:
https://github.com/apache/storm/pull/2218#discussion_r129803794
--- Diff:
storm-client/src/jvm/org/apache/storm/topology/WindowPartitionCache.java ---
@@ -0,0 +1,142 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.storm.topology;
+
+import java.util.concurrent.ConcurrentMap;
+
+/**
+ * A loading cache abstraction for caching {@link
PersistentWindowedBoltExecutor.WindowPartition}.
+ *
+ * @param <K> the key type
+ * @param <V> the value type
+ */
+public interface WindowPartitionCache<K, V> {
+
+ /**
+ * Get value from the cache or load the value.
+ *
+ * @param key the key
+ * @return the value
+ */
+ V get(K key);
+
+ /**
+ * Get value from the cache or load the value pinning it
+ * so that the entry will never get evicted.
+ *
+ * @param key the key
+ * @return the value
+ */
+ V getPinned(K key);
--- End diff --
This method name can be changed to `pinAndGet` as `getPinned` was implies
getting the value if it is pinned.
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