content: /*
   * Copyright 1999-2020 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
   *
   *      https://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.slots.block.degrade.circuitbreaker;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import com.alibaba.csp.sentinel.util.AssertUtil;
  
  /**
   * <p>Registry for circuit breaker event observers.</p>
   *
   * @author Eric Zhao
   * @since 1.8.0
   */
  public class EventObserverRegistry {
  
      private final Map<String, CircuitBreakerStateChangeObserver> stateChangeObserverMap = new HashMap<>();
  
      /**
       * Register a circuit breaker state change observer.
       *
       * @param name observer name
       * @param observer a valid observer
       */
      public void addStateChangeObserver(String name, CircuitBreakerStateChangeObserver observer) {
          AssertUtil.notNull(name, "name cannot be null");
          AssertUtil.notNull(observer, "observer cannot be null");
          stateChangeObserverMap.put(name, observer);
      }
  
      public boolean removeStateChangeObserver(String name) {
          AssertUtil.notNull(name, "name cannot be null");
          return stateChangeObserverMap.remove(name) != null;
      }
  
      /**
       * Get all registered state chane observers.
       *
       * @return all registered state chane observers
       */
      public List<CircuitBreakerStateChangeObserver> getStateChangeObservers() {
          return new ArrayList<>(stateChangeObserverMap.values());
      }
  
      public static EventObserverRegistry getInstance() {
          return InstanceHolder.instance;
      }
  
      private static class InstanceHolder {
          private static EventObserverRegistry instance = new EventObserverRegistry();
      }
  
      EventObserverRegistry() {}
  }
  