pd: use tokio_util::sync::PollSender in consensus svc
#436
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In v0.7 of `tokio-util`, the `PollSender` API was changed to have the semantics that most users expect (see tokio-rs/tokio#4214). The `poll_send_done` method was replaced with a `poll_reserve` method, and the implementation rewritten to drive a `Sender::reserve_owned` future that's consumed in `send_item`. Now, `PollSender` essentially implements exactly the same code that was written by hand in the consensus service. We can simplify the consensus service significantly by upgrading the `tokio-util` dependency to 0.7 and replacing the hand-written version with `PollSender`. There should be no functional change as a result of this refactor.
hawkw
commented
Feb 15, 2022
Comment on lines
44
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| let span = req.create_span(); | ||
| let (tx, rx) = oneshot::channel(); | ||
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| permit.send(Message { | ||
| req, | ||
| rsp_sender: tx, | ||
| span, | ||
| }); | ||
| self.queue |
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we may want to check if the channel is closed here and bail early (in case it closed between a successful poll_ready call and the call to call). i don't know how that matters in pd, specifically, though, since there's only ever going to be a single consensus background worker and it's expected to live for the entire lifetime of the node...if it's gone, panicking in the send_item call is probably also fine.
I didn't change this because the previous code didn't have such a check.
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In v0.7 of
tokio-util, thePollSenderAPI was changed to have thesemantics that most users expect (see tokio-rs/tokio#4214). The
poll_send_donemethod was replaced with apoll_reservemethod, andthe implementation rewritten to drive a
Sender::reserve_ownedfuturethat's consumed in
send_item. Now,PollSenderessentially implementsexactly the same code that was written by hand in the consensus service.
We can simplify the consensus service significantly by upgrading the
tokio-utildependency to 0.7 and replacing the hand-written versionwith
PollSender.There should be no functional change as a result of this refactor.