WebFlux pops scope before finishing transaction

[adinauer]

Discussed in #2694

Tested on WebFlux with Spring Boot 2.7.5 on our sample.

The doFinally blocks of SentryWebFilter (should pop scope at the very end) and SentryWebTracingFilter (should finish the transaction before scope is popped) seem to run in reverse order.

[adinauer]

This bug has been there since adding performance for WebFlux in 6.16.0. Spring Boot 3 is also affected.

[adinauer]

We could use doOnTerminate instead of doFinally in SentryWebTracingFilter to ensure the transaction is finished before scope is popped.

An alternative could be to not pop the scope and rely on the hub being garbage collected as we now always clone a new hub from the main hub for every request.

[adinauer]

Things I tried but didn't work:

A

• SentryWebFilter:
  • keep using doFinally
• SentryWebTracingFilter:
  • use doOnTerminate

Didn't work out because doOnError in SentryWebTracingFilter is called after doOnTerminate.

B

• SentryWebFilter:
  • keep using doFinally
• SentryWebTracingFilter:
  • use doAfterTerminate

Didn't work out because doFinally in SentryWebFilter is called before doAfterTerminate in SentryWebTracingFilter.

C

• SentryWebFilter:
  • use doAfterTerminate
• SentryWebTracingFilter:
  • use doFinally

Didn't work out because doAfterTerminate in SentryWebFilter is called before doFinally in SentryWebTracingFilter.

D

• SentryWebFilter:
  • use doAfterTerminate
• SentryWebTracingFilter:
  • use doAfterTerminate

Didn't work because doAfterTerminate in SentryWebFilter is called before doAfterTerminate in SentryWebTracingFilter

Other things we could try

• Not calling popScope
  • would hold on to memory until the thread is hit by another request
• Merging SentryWebFilter and SentryWebTracingFilter into one filter bean with configurable behaviour.