流控组件之Sentinel-代码简析

https://github.com/alibaba/Sentinel/wiki/How-it-works

1. 配置各种规则，然后通过aspectj解析注解然后看是否可以通过各种校验

@Aspect
public class SentinelResourceAspect extends AbstractSentinelAspectSupport {

    @Pointcut("@annotation(com.qxwz.sentinel.annotation.SentinelResource)")
    public void sentinelResourceAnnotationPointcut() {
    }

    @Around("sentinelResourceAnnotationPointcut()")
    public Object invokeResourceWithSentinel(ProceedingJoinPoint pjp) throws Throwable {
        Method originMethod = resolveMethod(pjp);

        SentinelResource annotation = originMethod.getAnnotation(SentinelResource.class);
        if (annotation == null) {
            // Should not go through here.
            throw new IllegalStateException("Wrong state for SentinelResource annotation");
        }
        String resourceName = getResourceName(annotation.value(), originMethod);
        EntryType entryType = annotation.entryType();
        Entry entry = null;
        try {
            entry = SphU.entry(resourceName, entryType, 1, pjp.getArgs());
            Object result = pjp.proceed();
            return result;
        } catch (BlockException ex) {
            return handleBlockException(pjp, annotation, ex);
        } catch (Throwable ex) {
            Class<? extends Throwable>[] exceptionsToIgnore = annotation.exceptionsToIgnore();
            // The ignore list will be checked first.
            if (exceptionsToIgnore.length > 0 && exceptionBelongsTo(ex, exceptionsToIgnore)) {
                throw ex;
            }
            if (exceptionBelongsTo(ex, annotation.exceptionsToTrace())) {
                traceException(ex, annotation);
                return handleFallback(pjp, annotation, ex);
            }

            // No fallback function can handle the exception, so throw it out.
            throw ex;
        } finally {
            if (entry != null) {
                entry.exit(1, pjp.getArgs());
            }
        }
    }
}

2. FlowRuleManager 动态规则（基于观察者模式）构建及监控（定时任务地调度metricTimerListener）

    private static final Map<String, List<FlowRule>> flowRules = new ConcurrentHashMap<String, List<FlowRule>>();

    private static final FlowPropertyListener LISTENER = new FlowPropertyListener();
    private static SentinelProperty<List<FlowRule>> currentProperty = new DynamicSentinelProperty<List<FlowRule>>();

    @SuppressWarnings("PMD.ThreadPoolCreationRule")
    private static final ScheduledExecutorService SCHEDULER = Executors.newScheduledThreadPool(1,
        new NamedThreadFactory("sentinel-metrics-record-task", true));

    static {
        currentProperty.addListener(LISTENER);
        SCHEDULER.scheduleAtFixedRate(new MetricTimerListener(), 0, 1, TimeUnit.SECONDS);
    }

3. 规则生效方法 - 基于滑动窗口的判断

4. 处理单元组织

FlowSlot 会根据预设的规则，结合前面 NodeSelectorSlot、ClusterNodeBuilderSlot、StatisticSlot 统计出来的实时信息进行流量控制，遍历所有限流规则，直到有规则触发限流或者所有规则遍历完毕。

5. 处理链条

6. 简单调用关系

SentinelResourceAspect.invokeResourceWithSentinel -> SphU.entry -> CtSph...lookProcessChain -> FlowSlot(checkFlow/fireEntry) -> DefaultController(canpass)