code: /*
   * 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.skywalking.oap.server.core.analysis.data;
  
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  import java.util.stream.Collectors;
  import org.apache.skywalking.oap.server.core.analysis.metrics.Metrics;
  import org.apache.skywalking.oap.server.core.storage.StorageID;
  
  /**
   * MergableBufferedData is a thread no safe implementation of {@link BufferedData}. {@link Metrics} in this cache would
   * be {@link Metrics#combine(Metrics)} if their {@link Metrics#id()}s are same.
   *
   * Concurrency {@link #accept(Metrics)}s and {@link #read()} while {@link #accept(Metrics)} are both not recommended.
   */
  public class MergableBufferedData<METRICS extends Metrics> implements BufferedData<METRICS> {
      private Map<StorageID, METRICS> buffer;
  
      public MergableBufferedData() {
          buffer = new HashMap<>();
      }
  
      /**
       * Accept the data into the cache and merge with the existing value.
       *
       * This method is not thread safe, should avoid concurrency calling.
       *
       * @param data to be added potentially.
       */
      @Override
      public void accept(final METRICS data) {
          final StorageID id = data.id();
          final METRICS existed = buffer.get(id);
          if (existed == null) {
              buffer.put(id, data);
          } else {
              existed.combine(data);
          }
      }
  
      @Override
      public List<METRICS> read() {
          try {
              return buffer.values().stream().collect(Collectors.toList());
          } finally {
              buffer.clear();
          }
      }
  }
  