Follow on from #17558
Basically, we want to reduce the number of threads we want to use at a
time, i.e. reduce the number of threads that are paused/blocked. We do
this by returning from the thread when the consumer pauses the producer,
rather than pausing in the thread.
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Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
