content: /*
   * 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.kafka.common.utils;
  
  import java.util.Collection;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentMap;
  
  /**
   * A simple read-optimized map implementation that synchronizes only writes and does a full copy on each modification.
   * <p>
   * Through the {@link org.apache.kafka.jmh.util.ConcurrentMapBenchmark}, we observed that in scenarios where
   * write operations (i.e. computeIfAbsent) constitute 10%, the get performance of CopyOnWriteMap is lower compared to
   * ConcurrentHashMap. However, when iterating over entrySet and values, CopyOnWriteMap performs better than ConcurrentHashMap.
   */
  public class CopyOnWriteMap<K, V> implements ConcurrentMap<K, V> {
  
      private volatile Map<K, V> map;
  
      public CopyOnWriteMap() {
          this.map = Collections.emptyMap();
      }
  
      public CopyOnWriteMap(Map<K, V> map) {
          this.map = Collections.unmodifiableMap(map);
      }
  
      @Override
      public boolean containsKey(Object k) {
          return map.containsKey(k);
      }
  
      @Override
      public boolean containsValue(Object v) {
          return map.containsValue(v);
      }
  
      @Override
      public Set<java.util.Map.Entry<K, V>> entrySet() {
          return map.entrySet();
      }
  
      @Override
      public V get(Object k) {
          return map.get(k);
      }
  
      @Override
      public boolean isEmpty() {
          return map.isEmpty();
      }
  
      @Override
      public Set<K> keySet() {
          return map.keySet();
      }
  
      @Override
      public int size() {
          return map.size();
      }
  
      @Override
      public Collection<V> values() {
          return map.values();
      }
  
      @Override
      public synchronized void clear() {
          this.map = Collections.emptyMap();
      }
  
      @Override
      public synchronized V put(K k, V v) {
          Map<K, V> copy = new HashMap<>(this.map);
          V prev = copy.put(k, v);
          this.map = Collections.unmodifiableMap(copy);
          return prev;
      }
  
      @Override
      public synchronized void putAll(Map<? extends K, ? extends V> entries) {
          Map<K, V> copy = new HashMap<>(this.map);
          copy.putAll(entries);
          this.map = Collections.unmodifiableMap(copy);
      }
  
      @Override
      public synchronized V remove(Object key) {
          Map<K, V> copy = new HashMap<>(this.map);
          V prev = copy.remove(key);
          this.map = Collections.unmodifiableMap(copy);
          return prev;
      }
  
      @Override
      public synchronized V putIfAbsent(K k, V v) {
          if (!containsKey(k))
              return put(k, v);
          else
              return get(k);
      }
  
      @Override
      public synchronized boolean remove(Object k, Object v) {
          if (containsKey(k) && get(k).equals(v)) {
              remove(k);
              return true;
          } else {
              return false;
          }
      }
  
      @Override
      public synchronized boolean replace(K k, V original, V replacement) {
          if (containsKey(k) && get(k).equals(original)) {
              put(k, replacement);
              return true;
          } else {
              return false;
          }
      }
  
      @Override
      public synchronized V replace(K k, V v) {
          if (containsKey(k)) {
              return put(k, v);
          } else {
              return null;
          }
      }
  
  }
  