Backport of "queue2: Avoid races when posting buffering messages" into 1.16
Backport of !511 (merged) "queue2: Avoid races when posting buffering messages".
Commits:
- 08d2d3cf queue2: Avoid races when posting buffering messages
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Backport of !511 (merged) "queue2: Avoid races when posting buffering messages".
Commits: