public interface CircuitBreaker {

    /**
     *  降级熔断规则
     */
    DegradeRule getRule();

    /**
     * true  判断需要降级
     */
    boolean tryPass(Context context);

    /**
     * 当前熔断器的状态
     */
    state currentState();

    /**
     * 回调方法   当请求pass通过后触发
     */
    void onRequestcomplete(Context context);

    /**
     * Circuit breaker state.
     */
    enum State {
      
        OPEN,
        
        HALF_OPEN,
       
        CLOSED
    }
}

void performChecking(Context context, ResourceWrapper r) throws BlockException {
        // 根据资源名  获取该资源的熔断器列表
        List<CircuitBreaker> circuitBreakers = DegradeRuleManager.getCircuitBreakers(r.getName());
        if (circuitBreakers == null || circuitBreakers.iSEMpty()) {
            return;
        }
        for (CircuitBreaker cb : circuitBreakers) {
            //逐次校验
            if (!cb.tryPass(context)) {
                throw new DegradeException(cb.getRule().getLimitApp(), cb.getRule());
            }
        }
    }

@override
    public boolean tryPass(Context context) {
        // Template implementation.
        if (currentState.get() == State.CLOSED) {
            return true;
        }
        // 若下次时间窗到达，且状态由open-> halfopen  则返回true
        if (currentState.get() == State.OPEN) {
            // For half-open state we allow a request for PRobing.
            // 校验是否通过的时候  有可能放开
            return retryTimeoutArrived() && FromOpenToHalfOpen(context);
        }
        return false;
    }

private final LeapArray<SimpleErrorCounter> stat;
private final LeapArray<SlowRequestCounter> slidingCounter;

 @Override
    public void (Context context) {
        Entry entry = context.getCurEntry();
        if (entry == null) {
            return;
        }
        // 非blockException
        Throwable error = entry.getError();
        // 这边也是使用滑动窗口统计
        SimpleErrorCounter counter = stat.currentWindow().value();
        if (error != null) {
            counter.getErrorCount().add(1);
        }
        counter.gettotalCount().add(1);

        handleStateChangeWhenThresholdExceeded(error);
    }

    private void handleStateChangeWhenThresholdExceeded(Throwable error) {
        if (currentState.get() == State.OPEN) {
            return;
        }
        
        if (currentState.get() == State.HALF_OPEN) {
            // In detecting request
            if (error == null) {
                fromHalfOpenToClose();
            } else {
                fromHalfOpenToOpen(1.0d);
            }
            return;
        }
        
        List<SimpleErrorCounter> counters = stat.values();
        long errCount = 0;
        long totalCount = 0;
        for (SimpleErrorCounter counter : counters) {
            errCount += counter.errorCount.sum();
            totalCount += counter.totalCount.sum();
        }
        if (totalCount < minRequestAmount) {
            return;
        }
        double curCount = errCount;
        if (strategy == DEGRADE_GRADE_EXCEPTION_RATIO) {
            // Use errorRatio
            curCount = errCount * 1.0d / totalCount;
        }
        if (curCount > threshold) {
            transformToOpen(curCount);
        }
    }