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 backtype.storm.state;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  /**
   * An in-memory implementation of the {@link State}
   */
  public class InMemoryKeyValueState<K, V> implements KeyValueState<K, V> {
      private static final Logger LOG = LoggerFactory.getLogger(InMemoryKeyValueState.class);
      private static final long DEFAULT_TXID = -1;
      private TxIdState<K, V> commitedState;
      private TxIdState<K, V> preparedState;
      private Map<K, V> state = new ConcurrentHashMap<>();
  
      private static class TxIdState<K, V> {
          private long txid;
          private Map<K, V> state;
  
          TxIdState(long txid, Map<K, V> state) {
              this.txid = txid;
              this.state = state;
          }
  
          @Override
          public String toString() {
              return "TxIdState{" + "txid=" + txid + ", state=" + state + '}';
          }
      }
  
      @Override
      public void put(K key, V value) {
          state.put(key, value);
      }
  
      @Override
      public V get(K key) {
          return state.get(key);
      }
  
      @Override
      public V get(K key, V defaultValue) {
          V val = get(key);
          return val != null ? val : defaultValue;
      }
  
      @Override
      public void commit() {
          commitedState = new TxIdState<>(DEFAULT_TXID, new ConcurrentHashMap<>(state));
      }
  
      @Override
      public void prepareCommit(long txid) {
          LOG.debug("prepare commit, txid {}", txid);
          if (preparedState != null && txid > preparedState.txid) {
              throw new RuntimeException("Cannot prepare a new txn while there is a pending txn");
          }
          preparedState = new TxIdState<>(txid, new ConcurrentHashMap<>(state));
      }
  
      @Override
      public void commit(long txid) {
          LOG.debug("commit, txid {}", txid);
          if (preparedState != null && txid == preparedState.txid) {
              commitedState = preparedState;
              preparedState = null;
          } else {
              throw new RuntimeException("Invalid prepared state for commit, " +
                      "preparedState " + preparedState + " txid " + txid);
          }
      }
  
      @Override
      public void rollback() {
          preparedState = null;
          if (commitedState != null) {
              state = commitedState.state;
          } else {
              state = new ConcurrentHashMap<>();
          }
      }
  
      @Override
      public String toString() {
          return "InMemoryKeyValueState{" +
                  "commitedState=" + commitedState +
                  ", preparedState=" + preparedState +
                  ", state=" + state +
                  '}';
      }
  }
  