docs(ch21-03): clarify channel state after sender drop (#4673)#4781
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docs(ch21-03): clarify channel state after sender drop (#4673)#4781Dodothereal wants to merge 1 commit into
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Fixes rust-lang#4673: 'When that happens' on its own doesn't distinguish between the buffered-message-still-drainable state and the sender-disconnected + buffer-empty state of mpsc channels. After drop(sender), workers can still recv() messages already in the queue; only when the buffer empties do recv() calls start returning Err. Replaced the single 'When that happens' with two clarifying sentences so the explanation lines up with the observed output in the graceful-shutdown run.
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Fixes #4673
Summary
In ch21-03, 'When that happens' immediately presupposes that
dropping the sender forces recv() to error, but mpsc channels can
still drain messages already buffered after the sender is dropped.
The discrete observation in the issue is that sample
graceful-shutdown output shows a worker still receiving a job after
the 'Shutting down worker N' message — consistent with buffering.
Add two short sentences flagging the buffered state. No code or
listing changed.
Test plan
AI assistance
Prepared with help from an AI coding assistant; reviewed end-to-end.