apollo-client/src/main/java/com/ctrip/framework/apollo/internals/DefaultConfigManager.java/DefaultConfigManager/getConfig
class DefaultConfigManager:  @Override
  public Config getConfig(String namespace) {
    Config config = m_configs.get(namespace);

    if (config == null) {
      synchronized (this) {
        config = m_configs.get(namespace);

        if (config == null) {
          ConfigFactory factory = m_factoryManager.getFactory(namespace);

          config = factory.create(namespace);
          m_configs.put(namespace, config);
        }
      }
    }

    return config;
  }