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.receiver.configuration.discovery;
  
  import com.google.common.hash.Hashing;
  import java.io.StringReader;
  import java.nio.charset.StandardCharsets;
  import java.util.HashMap;
  import org.apache.skywalking.oap.server.configuration.api.ConfigChangeWatcher;
  import org.apache.skywalking.oap.server.library.module.ModuleProvider;
  
  /**
   * AgentConfigurationsWatcher used to handle dynamic configuration changes.
   */
  public class AgentConfigurationsWatcher extends ConfigChangeWatcher {
      private volatile String settingsString;
      private volatile AgentConfigurationsTable agentConfigurationsTable;
      private final AgentConfigurations emptyAgentConfigurations;
  
      public AgentConfigurationsWatcher(ModuleProvider provider) {
          super(ConfigurationDiscoveryModule.NAME, provider, "agentConfigurations");
          this.settingsString = null;
          this.agentConfigurationsTable = new AgentConfigurationsTable();
          // noinspection UnstableApiUsage
          this.emptyAgentConfigurations = new AgentConfigurations(
              null, new HashMap<>(),
              Hashing.sha512().hashString("EMPTY", StandardCharsets.UTF_8).toString()
          );
      }
  
      @Override
      public void notify(ConfigChangeEvent value) {
          if (value.getEventType().equals(EventType.DELETE)) {
              settingsString = null;
              this.agentConfigurationsTable = new AgentConfigurationsTable();
          } else {
              settingsString = value.getNewValue();
              AgentConfigurationsReader agentConfigurationsReader =
                  new AgentConfigurationsReader(new StringReader(value.getNewValue()));
              this.agentConfigurationsTable = agentConfigurationsReader.readAgentConfigurationsTable();
          }
      }
  
      @Override
      public String value() {
          return settingsString;
      }
  
      /**
       * Get service dynamic configuration information, if there is no dynamic configuration information, return to empty
       * dynamic configuration to prevent the server from deleted the dynamic configuration, but it does not take effect
       * on the agent side.
       *
       * @param service Service name to be queried
       * @return Service dynamic configuration information
       */
      public AgentConfigurations getAgentConfigurations(String service) {
          AgentConfigurations agentConfigurations = agentConfigurationsTable.getAgentConfigurationsCache().get(service);
          if (null == agentConfigurations) {
              return emptyAgentConfigurations;
          } else {
              return agentConfigurations;
          }
      }
  }
  