Github user hanm commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/590#discussion_r219659865
--- Diff: src/java/main/org/apache/zookeeper/server/util/BitMap.java ---
@@ -0,0 +1,125 @@
+/**
+ * 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.zookeeper.server.util;
+
+import java.util.Map;
+import java.util.HashMap;
+import java.util.BitSet;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+
+/**
+ * This is a helper class to maintain the bit to specific value and the
+ * reversed value to bit mapping.
+ */
+public class BitMap<T> {
+
+ private final Map<T, Integer> value2Bit = new HashMap<T, Integer>();
+ private final Map<Integer, T> bit2Value = new HashMap<Integer, T>();
+
+ private final BitSet freedBitSet = new BitSet();
+ private Integer nextBit = Integer.valueOf(0);
+
+ private final ReentrantReadWriteLock rwLock = new
ReentrantReadWriteLock();
+
+ public Integer add(T value) {
+ Integer bit = getBit(value);
+ if (bit != null) {
+ return bit;
+ }
--- End diff --
I am also wondering, if this optimization is indeed useful, why not do the
same for the `remove` methods, that is, check and return early with a read lock
before trying to acquire a write lock.
---
