tokio-stream: add wrapper for broadcast and watch #3384

liufuyang · 2021-01-06T16:07:20Z

Signed-off-by: Fuyang Liu [email protected]

Motivation

Closes #3382

Solution

The basic sketch is going to be:

Make the constructor takes a broadcast receiver
Then it uses async-stream to turn that into an impl Stream
Still inside the constructor, call Box::pin on that stream, the put the pinned box into the struct
Then your impl Stream on Wrapper just forwards calls to poll_next to the pinned box

Darksonn · 2021-01-21T18:25:08Z

The Unpin bound can be removed once tokio-rs/async-stream#52 is released.

As for the Send/Sync bounds, I believe it would be sound to take them away with the right unsafe, but the question is if it's a good idea.

liufuyang · 2021-01-23T12:27:22Z

That sounds like some difficult question for me to answer :)

tokio-stream/src/wrappers/broadcast.rs

Darksonn · 2021-01-25T11:13:16Z

tokio-stream/src/wrappers/watch.rs

+pub struct WatchStream<T> {
+    inner: Pin<Box<dyn Stream<Item = ()>>>,
+    _marker: std::marker::PhantomData<T>,
+}


It seems like a problem to have the Stream return (). The user of the Stream would want the actual item, though I think we might have to clone it to do that?

🤔 I thought users would mostly use this to see whether something got arrived? (Maybe I am wrong...) Or maybe it is nice to have it return the last arrived value as well.

Or can I justyield rx.borrow() ? Instead of yield a ()? I am trying this and now having some difficulty to deal with the life-times.

Signed-off-by: Fuyang Liu <[email protected]>

Co-authored-by: Alice Ryhl <[email protected]>

* add watch * Fix up

tokio-stream/Cargo.toml

Darksonn · 2021-01-31T15:34:48Z

tokio-stream/src/wrappers/broadcast.rs

+    Ok((item, rx))
+}
+
+impl<T: Clone + Unpin + 'static + Send + Sync> BroadcastStream<T> {


With the new change, some of these bounds can be removed.

Darksonn · 2021-01-31T15:36:31Z

tokio-stream/src/wrappers/broadcast.rs

+/// [`tokio::sync::broadcast::Receiver`]: struct@tokio::sync::broadcast::Receiver
+/// [`Stream`]: trait@crate::Stream
+pub struct BroadcastStream<T> {
+    inner: ReusableBoxFuture<Result<(T, Receiver<T>), RecvError>>,


We need to return the receiver even if it emits an error, as the stream would otherwise not be usable again after returning an error.

Co-authored-by: Alice Ryhl <[email protected]>

Darksonn · 2021-01-31T16:27:46Z

tokio-stream/src/wrappers/broadcast.rs

+enum WrappedRecvError<T> {
+    Lagged(u64, Receiver<T>),
+    Closed,
+}
+
+async fn make_future<T: Clone>(
+    mut rx: Receiver<T>,
+) -> Result<(T, Receiver<T>), WrappedRecvError<T>> {
+    match rx.recv().await {
+        Ok(item) => Ok((item, rx)),
+        Err(RecvError::Lagged(n)) => Err(WrappedRecvError::Lagged(n, rx)),
+        Err(RecvError::Closed) => Err(WrappedRecvError::Closed),
+    }
+}


We should be able to simplify to the following.

Suggested change

enum WrappedRecvError<T> {

Lagged(u64, Receiver<T>),

Closed,

}

async fn make_future<T: Clone>(

mut rx: Receiver<T>,

) -> Result<(T, Receiver<T>), WrappedRecvError<T>> {

match rx.recv().await {

Ok(item) => Ok((item, rx)),

Err(RecvError::Lagged(n)) => Err(WrappedRecvError::Lagged(n, rx)),

Err(RecvError::Closed) => Err(WrappedRecvError::Closed),

}

}

async fn make_future<T: Clone>(

mut rx: Receiver<T>,

) -> (Result<T, RecvError<T>>, Receiver<T>) {

let result = rx.recv().await;

(result, rx)

}

That looks much better 😄

Darksonn · 2021-01-31T16:29:51Z

tokio-stream/src/wrappers/broadcast.rs

+        match ready!(self.inner.poll(cx)) {
+            Ok((item, rx)) => {
+                self.inner.set(make_future(rx));
+                Poll::Ready(Some(Ok(item)))
+            }
+            Err(err) => match err {
+                WrappedRecvError::Closed => Poll::Ready(None),
+                WrappedRecvError::Lagged(n, rx) => {
+                    self.inner.set(make_future(rx));
+                    Poll::Ready(Some(Err(BroadcastStreamRecvError::Lagged(n))))
+                }
+            },
+        }


I want to call self.inner.set(make_future(rx)) in all three cases because then, if the user calls poll_next after WrappedRecvError::Closed, then we will just return Poll::Ready(None) again.

With this implementation, it will panic if polled again after the first WrappedRecvError::Closed.

You should be able to avoid duplicating the call three times by doing it before the match (but after the self.inner.poll call).

That is a good catch. Thank you 👍

Darksonn · 2021-01-31T17:56:37Z

tokio-stream/src/wrappers/broadcast.rs

+        match result {
+            Ok(item) => Poll::Ready(Some(Ok(item))),
+            Err(err) => match err {
+                RecvError::Closed => Poll::Ready(None),
+                RecvError::Lagged(n) => Poll::Ready(Some(Err(BroadcastStreamRecvError::Lagged(n)))),
+            },
+        }


This could be simplified.

Suggested change

match result {

Ok(item) => Poll::Ready(Some(Ok(item))),

Err(err) => match err {

RecvError::Closed => Poll::Ready(None),

RecvError::Lagged(n) => Poll::Ready(Some(Err(BroadcastStreamRecvError::Lagged(n)))),

},

}

match result {

Ok(item) => Poll::Ready(Some(Ok(item))),

Err(RecvError::Closed) => Poll::Ready(None),

Err(RecvError::Lagged(n)) => Poll::Ready(Some(Err(BroadcastStreamRecvError::Lagged(n)))),

}

Darksonn · 2021-01-31T17:57:25Z

tokio-stream/src/wrappers/broadcast.rs

+    }
+}
+
+impl<T: Clone> fmt::Debug for BroadcastStream<T> {


Suggested change

impl<T: Clone> fmt::Debug for BroadcastStream<T> {

impl<T> fmt::Debug for BroadcastStream<T> {

Darksonn · 2021-01-31T17:59:17Z

tokio-stream/src/wrappers/watch.rs

+async fn make_future<T: Clone + Send + Sync>(
+    mut rx: Receiver<T>,
+) -> Result<((), Receiver<T>), RecvError> {
+    let signal = rx.changed().await?;
+    Ok((signal, rx))
+}


Same change here.

Aha, sorry I forgot this one.

Darksonn

This seems good to me now!

## Issue Addressed resolves #2129 resolves #2099 addresses some of #1712 unblocks #2076 unblocks #2153 ## Proposed Changes - Updates all the dependencies mentioned in #2129, except for web3. They haven't merged their tokio 1.0 update because they are waiting on some dependencies of their own. Since we only use web3 in tests, I think updating it in a separate issue is fine. If they are able to merge soon though, I can update in this PR. - Updates `tokio_util` to 0.6.2 and `bytes` to 1.0.1. - We haven't made a discv5 release since merging tokio 1.0 updates so I'm using a commit rather than release atm. **Edit:** I think we should merge an update of `tokio_util` to 0.6.2 into discv5 before this release because it has panic fixes in `DelayQueue` --> PR in discv5: sigp/discv5#58 ## Additional Info tokio 1.0 changes that required some changes in lighthouse: - `interval.next().await.is_some()` -> `interval.tick().await` - `sleep` future is now `!Unpin` -> tokio-rs/tokio#3028 - `try_recv` has been temporarily removed from `mpsc` -> tokio-rs/tokio#3350 - stream features have moved to `tokio-stream` and `broadcast::Receiver::into_stream()` has been temporarily removed -> `tokio-rs/tokio#2870 - I've copied over the `BroadcastStream` wrapper from this PR, but can update to use `tokio-stream` once it's merged tokio-rs/tokio#3384 Co-authored-by: realbigsean <[email protected]>

taiki-e added A-tokio-stream Area: The tokio-stream crate M-stream Module: tokio/stream labels Jan 10, 2021

Darksonn reviewed Jan 23, 2021

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liufuyang force-pushed the tokio-stream-3382 branch 2 times, most recently from 354649a to f1c0143 Compare January 24, 2021 10:08

Darksonn reviewed Jan 24, 2021

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tokio-stream/src/wrappers/broadcast.rs Show resolved Hide resolved

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liufuyang changed the title ~~tokio-stream: add wrapper for broadcast~~ tokio-stream: add wrapper for broadcast and watch Jan 25, 2021

Darksonn reviewed Jan 25, 2021

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realbigsean mentioned this pull request Jan 25, 2021

[Merged by Bors] - Update to tokio 1.1 sigp/lighthouse#2172

Closed

liufuyang force-pushed the tokio-stream-3382 branch from c6bc555 to 3957c05 Compare January 26, 2021 12:41

liufuyang and others added 11 commits January 31, 2021 14:39

tokio-stream: add wrapper for broadcast

eddbdaa

Signed-off-by: Fuyang Liu <[email protected]>

Fix up

f1094aa

Signed-off-by: Fuyang Liu <[email protected]>

Minor fixup - remove cfg_attr

6995914

Add #[derive(Debug)]

5229cad

Update tokio-stream/src/wrappers/broadcast.rs

c611d5c

Co-authored-by: Alice Ryhl <[email protected]>

return Lagged error

1977be3

expose BroadcastStreamRecvError

d9fd015

reformat

9513b71

add watch (#1)

ed00803

* add watch * Fix up

return cloned value when warpped recv changed

ef12286

remove dependency of async_stream

34eab73

liufuyang force-pushed the tokio-stream-3382 branch from 3957c05 to 34eab73 Compare January 31, 2021 15:28

Darksonn reviewed Jan 31, 2021

View reviewed changes

liufuyang and others added 3 commits January 31, 2021 16:51

Update tokio-stream/Cargo.toml

c6f9ee9

Co-authored-by: Alice Ryhl <[email protected]>

wrap the receiver in an inner error

35a8502

fix up

2cbf560

Darksonn reviewed Jan 31, 2021

View reviewed changes

simplify code

e2d8214

liufuyang added 2 commits January 31, 2021 18:36

alwasy refresh inner future

f7f2f00

add async-stream back for dev dep

fb244b1

Darksonn reviewed Jan 31, 2021

View reviewed changes

liufuyang added 2 commits January 31, 2021 19:09

simplify code

3b045dc

fix up

d44d54a

Darksonn approved these changes Jan 31, 2021

View reviewed changes

Darksonn merged commit 1c1e0e3 into tokio-rs:master Feb 5, 2021

Darksonn mentioned this pull request Feb 5, 2021

chore: prepare tokio-stream 0.1.3 #3507

Merged

liufuyang deleted the tokio-stream-3382 branch February 6, 2021 09:59

paulhauner mentioned this pull request Feb 10, 2021

Use tokio-stream BroadcastStream sigp/lighthouse#2189

Closed

dependabot bot mentioned this pull request Mar 8, 2021

Bump tokio from 0.2.25 to 1.2.0 technic/epg-server#135

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dependabot bot mentioned this pull request Mar 17, 2021

Bump tokio from 0.2.23 to 1.2.0 predominant/habitat#3

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tokio-stream: add wrapper for broadcast and watch #3384

tokio-stream: add wrapper for broadcast and watch #3384

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	impl<T: Clone> fmt::Debug for BroadcastStream<T> {
	impl<T> fmt::Debug for BroadcastStream<T> {

tokio-stream: add wrapper for broadcast and watch #3384

tokio-stream: add wrapper for broadcast and watch #3384

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liufuyang commented Jan 6, 2021

Motivation

Solution

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Darksonn commented Jan 21, 2021 •

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