Since the start of "Druid PR checklist review" initiative ( http://mail-archives.apache.org/mod_mbox/druid-dev/201811.mbox/%3CCAAMLo=ak_wlsvky1ptvradyzliz_znx5cgqkbdyhtjz3ztr...@mail.gmail.com%3E) we finalized (more or less) a block of items that concern concurrency. I've published them as a separate blog post: https://medium.com/@leventov/code-review-checklist-java-concurrency-49398c326154
Not only new PRs can be reviewed; it's very useful to review old code too. Here is a project about going through old Druid classes with concurrency and improve them: https://github.com/apache/incubator-druid/issues/7061. Everybody is welcome to pick up some class and improve it.
