Add an automatic flushing mechanism for RxNetty [SPR-14991]

[spring-projects-issues]

Sébastien Deleuze opened SPR-14991 and commented

As discussed on this issue, RxNetty does not provide any automatic flushing mechanism and block when the send buffer is full. Our RxNetty integration should implement a flush selector based mechanism to flush the data automatically (for example after sending 8K of data).

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This issue is a sub-task of #19510

Referenced from: commits 24b3614

[spring-projects-issues]

Sébastien Deleuze commented

Fixed by this commit, and spring-boot-reactive-netty-output-rxnetty example app now works flawlessly with iteration > 184.