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.slots.block.degrade.circuitbreaker;
  
  import java.util.concurrent.atomic.AtomicReference;
  
  import com.alibaba.csp.sentinel.Entry;
  import com.alibaba.csp.sentinel.context.Context;
  import com.alibaba.csp.sentinel.slotchain.ResourceWrapper;
  import com.alibaba.csp.sentinel.slots.block.degrade.DegradeRule;
  import com.alibaba.csp.sentinel.slots.block.degrade.DegradeRuleManager;
  import com.alibaba.csp.sentinel.util.AssertUtil;
  import com.alibaba.csp.sentinel.util.TimeUtil;
  import com.alibaba.csp.sentinel.util.function.BiConsumer;
  
  /**
   * @author Eric Zhao
   * @since 1.8.0
   */
  public abstract class AbstractCircuitBreaker implements CircuitBreaker {
  
      protected final DegradeRule rule;
      protected final int recoveryTimeoutMs;
  
      private final EventObserverRegistry observerRegistry;
  
      protected final AtomicReference<State> currentState = new AtomicReference<>(State.CLOSED);
      protected volatile long nextRetryTimestamp;
  
      public AbstractCircuitBreaker(DegradeRule rule) {
          this(rule, EventObserverRegistry.getInstance());
      }
  
      AbstractCircuitBreaker(DegradeRule rule, EventObserverRegistry observerRegistry) {
          AssertUtil.notNull(observerRegistry, "observerRegistry cannot be null");
          if (!DegradeRuleManager.isValidRule(rule)) {
              throw new IllegalArgumentException("Invalid DegradeRule: " + rule);
          }
          this.observerRegistry = observerRegistry;
          this.rule = rule;
          this.recoveryTimeoutMs = rule.getTimeWindow() * 1000;
      }
  
      @Override
      public DegradeRule getRule() {
          return rule;
      }
  
      @Override
      public State currentState() {
          return currentState.get();
      }
  
      @Override
      public boolean tryPass(Context context) {
          // Template implementation.
          if (currentState.get() == State.CLOSED) {
              return true;
          }
          if (currentState.get() == State.OPEN) {
              // For half-open state we allow a request for probing.
              return retryTimeoutArrived() && fromOpenToHalfOpen(context);
          }
          return false;
      }
  
      /**
       * Reset the statistic data.
       */
      abstract void resetStat();
  
      protected boolean retryTimeoutArrived() {
          return TimeUtil.currentTimeMillis() >= nextRetryTimestamp;
      }
  
      protected void updateNextRetryTimestamp() {
          this.nextRetryTimestamp = TimeUtil.currentTimeMillis() + recoveryTimeoutMs;
      }
  
      protected boolean fromCloseToOpen(double snapshotValue) {
          State prev = State.CLOSED;
          if (currentState.compareAndSet(prev, State.OPEN)) {
              updateNextRetryTimestamp();
  
              notifyObservers(prev, State.OPEN, snapshotValue);
              return true;
          }
          return false;
      }
  
      protected boolean fromOpenToHalfOpen(Context context) {
          if (currentState.compareAndSet(State.OPEN, State.HALF_OPEN)) {
              notifyObservers(State.OPEN, State.HALF_OPEN, null);
              Entry entry = context.getCurEntry();
              entry.whenTerminate(new BiConsumer<Context, Entry>() {
                  @Override
                  public void accept(Context context, Entry entry) {
                      // Note: This works as a temporary workaround for https://github.com/alibaba/Sentinel/issues/1638
                      // Without the hook, the circuit breaker won't recover from half-open state in some circumstances
                      // when the request is actually blocked by upcoming rules (not only degrade rules).
                      if (entry.getBlockError() != null) {
                          // Fallback to OPEN due to detecting request is blocked
                          currentState.compareAndSet(State.HALF_OPEN, State.OPEN);
                          notifyObservers(State.HALF_OPEN, State.OPEN, 1.0d);
                      }
                  }
              });
              return true;
          }
          return false;
      }
      
      private void notifyObservers(CircuitBreaker.State prevState, CircuitBreaker.State newState, Double snapshotValue) {
          for (CircuitBreakerStateChangeObserver observer : observerRegistry.getStateChangeObservers()) {
              observer.onStateChange(prevState, newState, rule, snapshotValue);
          }
      }
  
      protected boolean fromHalfOpenToOpen(double snapshotValue) {
          if (currentState.compareAndSet(State.HALF_OPEN, State.OPEN)) {
              updateNextRetryTimestamp();
              notifyObservers(State.HALF_OPEN, State.OPEN, snapshotValue);
              return true;
          }
          return false;
      }
  
      protected boolean fromHalfOpenToClose() {
          if (currentState.compareAndSet(State.HALF_OPEN, State.CLOSED)) {
              resetStat();
              notifyObservers(State.HALF_OPEN, State.CLOSED, null);
              return true;
          }
          return false;
      }
  
      protected void transformToOpen(double triggerValue) {
          State cs = currentState.get();
          switch (cs) {
              case CLOSED:
                  fromCloseToOpen(triggerValue);
                  break;
              case HALF_OPEN:
                  fromHalfOpenToOpen(triggerValue);
                  break;
              default:
                  break;
          }
      }
  }
  