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
   * <p>
   * http://www.apache.org/licenses/LICENSE-2.0
   * <p>
   * 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 storm.trident.windowing;
  
  import java.io.Serializable;
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Enumeration;
  import java.util.Iterator;
  import java.util.List;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicInteger;
  
  /**
   * In-memory store implementation of {@code WindowsStore} which can be backed by persistent store.
   */
  public class InMemoryWindowsStore implements WindowsStore, Serializable {
  
      private final ConcurrentHashMap<String, Object> store = new ConcurrentHashMap<>();
  
      private int maxSize;
      private AtomicInteger currentSize;
      private WindowsStore backingStore;
  
      public InMemoryWindowsStore() {
      }
  
      /**
       * @param maxSize      maximum size of in-memory store
       * @param backingStore backing store containing the entries
       */
      public InMemoryWindowsStore(int maxSize, WindowsStore backingStore) {
          this.maxSize = maxSize;
          currentSize = new AtomicInteger();
          this.backingStore = backingStore;
      }
  
      @Override
      public Object get(String key) {
          Object value = store.get(key);
  
          if (value == null && backingStore != null) {
              value = backingStore.get(key);
          }
  
          return value;
      }
  
      @Override
      public Iterable<Object> get(List<String> keys) {
          List<Object> values = new ArrayList<>();
          for (String key : keys) {
              values.add(get(key));
          }
          return values;
      }
  
      @Override
      public Iterable<String> getAllKeys() {
          if (backingStore != null) {
              return backingStore.getAllKeys();
          }
  
          final Enumeration<String> storeEnumeration = store.keys();
          final Iterator<String> resultIterator = new Iterator<String>() {
              @Override
              public boolean hasNext() {
                  return storeEnumeration.hasMoreElements();
              }
  
              @Override
              public String next() {
                  return storeEnumeration.nextElement();
              }
  
              @Override
              public void remove() {
                  throw new UnsupportedOperationException("remove operation is not supported as it is immutable.");
              }
          };
  
          return new Iterable<String>() {
              @Override
              public Iterator<String> iterator() {
                  return resultIterator;
              }
          };
      }
  
      @Override
      public void put(String key, Object value) {
          _put(key, value);
  
          if (backingStore != null) {
              backingStore.put(key, value);
          }
      }
  
      private void _put(String key, Object value) {
          if (!canAdd()) {
              return;
          }
  
          store.put(key, value);
          incrementCurrentSize();
      }
  
      private void incrementCurrentSize() {
          if (backingStore != null) {
              currentSize.incrementAndGet();
          }
      }
  
      private boolean canAdd() {
          return backingStore == null || currentSize.get() < maxSize;
      }
  
      @Override
      public void putAll(Collection<Entry> entries) {
          for (Entry entry : entries) {
              _put(entry.key, entry.value);
          }
          if (backingStore != null) {
              backingStore.putAll(entries);
          }
      }
  
      @Override
      public void remove(String key) {
          _remove(key);
  
          if (backingStore != null) {
              backingStore.remove(key);
          }
      }
  
      private void _remove(String key) {
          Object oldValue = store.remove(key);
  
          if (oldValue != null) {
              decrementSize();
              if (backingStore != null) {
                  backingStore.remove(key);
              }
          }
  
      }
  
      private void decrementSize() {
          if (backingStore != null) {
              currentSize.decrementAndGet();
          }
      }
  
      @Override
      public void removeAll(Collection<String> keys) {
          for (String key : keys) {
              _remove(key);
          }
  
          if (backingStore != null) {
              backingStore.removeAll(keys);
          }
      }
  
      @Override
      public void shutdown() {
          store.clear();
  
          if (backingStore != null) {
              backingStore.shutdown();
          }
      }
  
      @Override
      public String toString() {
          return "InMemoryWindowsStore{" +
                  " store:size = " + store.size() +
                  " backingStore = " + backingStore +
                  '}';
      }
  }
  