storm-core/src/jvm/org/apache/storm/state/InMemoryKeyValueStateProvider.java

/**
 * 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.state;

import org.apache.storm.task.TopologyContext;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Provides {@link InMemoryKeyValueState}
 */
public class InMemoryKeyValueStateProvider implements StateProvider {
    private final ConcurrentHashMap<String, State> states = new ConcurrentHashMap<>();

    @Override
    public State newState(String namespace, Map stormConf, TopologyContext context) {
        State state = states.get(namespace);
        if (state == null) {
            State newState = new InMemoryKeyValueState<>();
            state = states.putIfAbsent(namespace, newState);
            if (state == null) {
                state = newState;
            }
        }
        return state;
    }
}