Documentation issue maybe

Hi all, I think the code example in following section has a thread safety issue: https://ci.apache.org/projects/flink/flink-docs-release-1.9/dev/stream/testing.html#junit-rule-miniclusterwithclientresource The class CollectSink is not thread safe as only the write to the values collection are sync

Side outputs in Async I/O

Hi flink, I would like to know if you think that providing access to the side output from Async I/O cloud be a good idea. Thanks in advance, Romain