content: /*
   * Copyright 1999-2019 Alibaba Group Holding Ltd.
   *
   * Licensed 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 com.alibaba.csp.sentinel.metric.extension;
  
  import java.util.ArrayList;
  import java.util.List;
  
  import com.alibaba.csp.sentinel.log.RecordLog;
  import com.alibaba.csp.sentinel.spi.SpiLoader;
  
  /**
   * Get all {@link MetricExtension} via SPI.
   *
   * @author Carpenter Lee
   * @since 1.6.1
   */
  public class MetricExtensionProvider {
      private static List<MetricExtension> metricExtensions = new ArrayList<>();
  
      static {
          resolveInstance();
      }
  
      private static void resolveInstance() {
          List<MetricExtension> extensions = SpiLoader.of(MetricExtension.class).loadInstanceList();
  
          if (extensions.isEmpty()) {
              RecordLog.info("[MetricExtensionProvider] No existing MetricExtension found");
          } else {
              metricExtensions.addAll(extensions);
              RecordLog.info("[MetricExtensionProvider] MetricExtension resolved, size={}", extensions.size());
          }
      }
  
      /**
       * <p>Get all registered metric extensions.</p>
       * <p>DO NOT MODIFY the returned list, use {@link #addMetricExtension(MetricExtension)}.</p>
       *
       * @return all registered metric extensions
       */
      public static List<MetricExtension> getMetricExtensions() {
          return metricExtensions;
      }
  
      /**
       * Add metric extension.
       * <p>
       * Note that this method is NOT thread safe.
       * </p>
       *
       * @param metricExtension the metric extension to add.
       */
      public static void addMetricExtension(MetricExtension metricExtension) {
          metricExtensions.add(metricExtension);
      }
  
  }
  