Actually, when the invocation completes (whether successful or with error), we need to call e.Exit() to mark it as completed, or the response time, complete count and error count will be lost. We may need to carry the *SentinelEntry in the RPC context (if possible) and handle it in OnResponse callback.

FYI: onResponse logic in Java version (1.7.1)

please check it

Can we also provide a fallback registry where developers could register their own fallback logic when blocked? We could provide the default behavior.

Refer: https://github.com/alibaba/Sentinel/tree/1.7.1/sentinel-adapter/sentinel-apache-dubbo-adapter/src/main/java/com/alibaba/csp/sentinel/adapter/dubbo/fallback

please check it

What're the differences between async and sync mode?

This is mainly to see that in Java code, async entry is used instead of entry to restrict current. At this stage, Dubbo go has not added async field in attachment, so it will not come to async logic

Okay. Sentinel Go has unified entry and asyncEntry, so we could use sentinel.Entry(args) for both sync and async scenarios.