Incorrect entry-exit state when assembling multiple chained SentinelReactorTransformer

[sczyh30]

Issue Description

Type: bug report

Describe what happened (or what feature you want)

Incorrect entry-exit state when assembling multiple chained SentinelReactorTransformer like this:

upstream
  .transform(new SentinelReactorTransformer<>("reactor-service-a"))
  .transform(new SentinelReactorTransformer<>("reactor-service-b"))

When the flow control for the latter resource (e.g. reactor-service-b) is triggered, the SentinelReactorSubscriber will signal cancel() and propagate the BlockException, but the SentinelReactorSubscriber did not handle the hookOnCancel appropriately, thus causing the AsyncEntry of the former resource reactor-service-a not exited.

Describe what you expected to happen

The onCancel() signal should be handled correctly, so the entry could be exited.

How to reproduce it (as minimally and precisely as possible)

Run this code snippet:

public static void main(String[] args) throws Exception {
    FlowRuleManager.loadRules(
        Arrays.asList(new FlowRule("reactor-service-b").setCount(0))
    );
    Mono.just(2)
        .transform(new SentinelReactorTransformer<>("reactor-service-a"))
        .transform(new SentinelReactorTransformer<>("reactor-service-b"))
        .subscribe(System.out::println, Throwable::printStackTrace);
}

We set a FlowRule for resource reactor-service-b to disallow its invocation. After the code snippet is executed, we could find that the inner AsyncEntry for reactor-service-a is not exited.

1571105350000|2019-10-15 10:09:10|reactor-service-a|1|0|0|0|0|0
1571105350000|2019-10-15 10:09:10|reactor-service-b|0|1|0|0|0|0

Tell us your environment

Sentinel 1.7.0-SNAPSHOT on master branch.