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;
  
  import org.apache.skywalking.oap.server.core.config.ComponentLibraryCatalogService;
  
  /**
   * ComponentLibraryCatalogUtil provides convenience access for {@link ComponentLibraryCatalogService} service in the
   * core module's default provider.
   * Notice, this util should not be used out of the core module's default provide, otherwise, it breaks the isolation
   * cross modules.
   *
   * @since 9.4.0
   */
  public class ComponentLibraryCatalogUtil {
      private static ComponentLibraryCatalogService REF;
  
      public static ComponentLibraryCatalogService hold(final ComponentLibraryCatalogService ref) {
          if (REF != null) {
              throw new IllegalStateException("REF had been initialized. Repeatedly initialization is not allowed");
          }
          ComponentLibraryCatalogUtil.REF = ref;
          return ComponentLibraryCatalogUtil.REF;
      }
  
      public static ComponentLibraryCatalogService get() {
          if (REF == null) {
              throw new IllegalStateException("REF is not initialized");
          }
          return REF;
      }
  }
  