New issue
Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.
By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.
Already on GitHub? Sign in to your account
Introduce stream::select_with_strategy #2450
Merged
taiki-e
merged 7 commits into
rust-lang:master
from
najamelan:feature/stream_select_bias
Jun 17, 2021
Merged
Changes from all commits
Commits
Show all changes
7 commits
Select commit
Hold shift + click to select a range
b5bd8fe
Introduce futures_util::stream::select_bias.
najamelan 9a66962
Fix review feedback.
najamelan ebe59eb
Rename to select_with_strategy.
najamelan 37f2dee
Re-implement `futures-util::stream::select` in function of `select_wi…
najamelan 0aab927
Please cargo fmt...
najamelan 34c4a00
Use futures crate instead of futures_util in examples.
najamelan e8a17f9
Give SelectWithStrategy a custom fmt::Debug impl.
najamelan File filter
Filter by extension
Conversations
Failed to load comments.
Jump to
Jump to file
Failed to load files.
Diff view
Diff view
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,230 @@ | ||
use super::assert_stream; | ||
use crate::stream::{Fuse, StreamExt}; | ||
use core::{fmt, pin::Pin}; | ||
use futures_core::stream::{FusedStream, Stream}; | ||
use futures_core::task::{Context, Poll}; | ||
use pin_project_lite::pin_project; | ||
|
||
/// Type to tell [`SelectWithStrategy`] which stream to poll next. | ||
#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)] | ||
pub enum PollNext { | ||
/// Poll the first stream. | ||
Left, | ||
/// Poll the second stream. | ||
Right, | ||
} | ||
|
||
impl PollNext { | ||
/// Toggle the value and return the old one. | ||
pub fn toggle(&mut self) -> Self { | ||
let old = *self; | ||
|
||
match self { | ||
PollNext::Left => *self = PollNext::Right, | ||
PollNext::Right => *self = PollNext::Left, | ||
} | ||
|
||
old | ||
} | ||
} | ||
|
||
impl Default for PollNext { | ||
fn default() -> Self { | ||
PollNext::Left | ||
} | ||
} | ||
|
||
pin_project! { | ||
/// Stream for the [`select_with_strategy()`] function. See function docs for details. | ||
#[must_use = "streams do nothing unless polled"] | ||
pub struct SelectWithStrategy<St1, St2, Clos, State> { | ||
#[pin] | ||
stream1: Fuse<St1>, | ||
#[pin] | ||
stream2: Fuse<St2>, | ||
state: State, | ||
clos: Clos, | ||
} | ||
} | ||
|
||
/// This function will attempt to pull items from both streams. You provide a | ||
/// closure to tell [`SelectWithStrategy`] which stream to poll. The closure can | ||
/// store state on `SelectWithStrategy` to which it will receive a `&mut` on every | ||
/// invocation. This allows basing the strategy on prior choices. | ||
/// | ||
/// After one of the two input streams completes, the remaining one will be | ||
/// polled exclusively. The returned stream completes when both input | ||
/// streams have completed. | ||
/// | ||
/// Note that this function consumes both streams and returns a wrapped | ||
/// version of them. | ||
/// | ||
/// ## Examples | ||
/// | ||
/// ### Priority | ||
/// This example shows how to always prioritize the left stream. | ||
/// | ||
/// ```rust | ||
/// # futures::executor::block_on(async { | ||
/// use futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt }; | ||
/// | ||
/// let left = repeat(1); | ||
/// let right = repeat(2); | ||
/// | ||
/// // We don't need any state, so let's make it an empty tuple. | ||
/// // We must provide some type here, as there is no way for the compiler | ||
/// // to infer it. As we don't need to capture variables, we can just | ||
/// // use a function pointer instead of a closure. | ||
/// fn prio_left(_: &mut ()) -> PollNext { PollNext::Left } | ||
/// | ||
/// let mut out = select_with_strategy(left, right, prio_left); | ||
/// | ||
/// for _ in 0..100 { | ||
/// // Whenever we poll out, we will alwas get `1`. | ||
/// assert_eq!(1, out.select_next_some().await); | ||
/// } | ||
/// # }); | ||
/// ``` | ||
/// | ||
/// ### Round Robin | ||
/// This example shows how to select from both streams round robin. | ||
/// Note: this special case is provided by [`futures-util::stream::select`]. | ||
/// | ||
/// ```rust | ||
/// # futures::executor::block_on(async { | ||
/// use futures::stream::{ repeat, select_with_strategy, PollNext, StreamExt }; | ||
/// | ||
/// let left = repeat(1); | ||
/// let right = repeat(2); | ||
/// | ||
/// // We don't need any state, so let's make it an empty tuple. | ||
/// let rrobin = |last: &mut PollNext| last.toggle(); | ||
/// | ||
/// let mut out = select_with_strategy(left, right, rrobin); | ||
/// | ||
/// for _ in 0..100 { | ||
/// // We should be alternating now. | ||
/// assert_eq!(1, out.select_next_some().await); | ||
/// assert_eq!(2, out.select_next_some().await); | ||
/// } | ||
/// # }); | ||
/// ``` | ||
pub fn select_with_strategy<St1, St2, Clos, State>( | ||
stream1: St1, | ||
stream2: St2, | ||
which: Clos, | ||
) -> SelectWithStrategy<St1, St2, Clos, State> | ||
where | ||
St1: Stream, | ||
St2: Stream<Item = St1::Item>, | ||
Clos: FnMut(&mut State) -> PollNext, | ||
State: Default, | ||
{ | ||
assert_stream::<St1::Item, _>(SelectWithStrategy { | ||
stream1: stream1.fuse(), | ||
stream2: stream2.fuse(), | ||
state: Default::default(), | ||
clos: which, | ||
}) | ||
} | ||
|
||
impl<St1, St2, Clos, State> SelectWithStrategy<St1, St2, Clos, State> { | ||
/// Acquires a reference to the underlying streams that this combinator is | ||
/// pulling from. | ||
pub fn get_ref(&self) -> (&St1, &St2) { | ||
(self.stream1.get_ref(), self.stream2.get_ref()) | ||
} | ||
|
||
/// Acquires a mutable reference to the underlying streams that this | ||
/// combinator is pulling from. | ||
/// | ||
/// Note that care must be taken to avoid tampering with the state of the | ||
/// stream which may otherwise confuse this combinator. | ||
pub fn get_mut(&mut self) -> (&mut St1, &mut St2) { | ||
(self.stream1.get_mut(), self.stream2.get_mut()) | ||
} | ||
|
||
/// Acquires a pinned mutable reference to the underlying streams that this | ||
/// combinator is pulling from. | ||
/// | ||
/// Note that care must be taken to avoid tampering with the state of the | ||
/// stream which may otherwise confuse this combinator. | ||
pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>) { | ||
let this = self.project(); | ||
(this.stream1.get_pin_mut(), this.stream2.get_pin_mut()) | ||
} | ||
|
||
/// Consumes this combinator, returning the underlying streams. | ||
/// | ||
/// Note that this may discard intermediate state of this combinator, so | ||
/// care should be taken to avoid losing resources when this is called. | ||
pub fn into_inner(self) -> (St1, St2) { | ||
(self.stream1.into_inner(), self.stream2.into_inner()) | ||
} | ||
} | ||
|
||
impl<St1, St2, Clos, State> FusedStream for SelectWithStrategy<St1, St2, Clos, State> | ||
where | ||
St1: Stream, | ||
St2: Stream<Item = St1::Item>, | ||
Clos: FnMut(&mut State) -> PollNext, | ||
{ | ||
fn is_terminated(&self) -> bool { | ||
self.stream1.is_terminated() && self.stream2.is_terminated() | ||
} | ||
} | ||
|
||
impl<St1, St2, Clos, State> Stream for SelectWithStrategy<St1, St2, Clos, State> | ||
where | ||
St1: Stream, | ||
St2: Stream<Item = St1::Item>, | ||
Clos: FnMut(&mut State) -> PollNext, | ||
{ | ||
type Item = St1::Item; | ||
|
||
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> { | ||
let this = self.project(); | ||
|
||
match (this.clos)(this.state) { | ||
PollNext::Left => poll_inner(this.stream1, this.stream2, cx), | ||
PollNext::Right => poll_inner(this.stream2, this.stream1, cx), | ||
} | ||
} | ||
} | ||
|
||
fn poll_inner<St1, St2>( | ||
a: Pin<&mut St1>, | ||
b: Pin<&mut St2>, | ||
cx: &mut Context<'_>, | ||
) -> Poll<Option<St1::Item>> | ||
where | ||
St1: Stream, | ||
St2: Stream<Item = St1::Item>, | ||
{ | ||
let a_done = match a.poll_next(cx) { | ||
Poll::Ready(Some(item)) => return Poll::Ready(Some(item)), | ||
Poll::Ready(None) => true, | ||
Poll::Pending => false, | ||
}; | ||
|
||
match b.poll_next(cx) { | ||
Poll::Ready(Some(item)) => Poll::Ready(Some(item)), | ||
Poll::Ready(None) if a_done => Poll::Ready(None), | ||
Poll::Ready(None) | Poll::Pending => Poll::Pending, | ||
} | ||
} | ||
|
||
impl<St1, St2, Clos, State> fmt::Debug for SelectWithStrategy<St1, St2, Clos, State> | ||
where | ||
St1: fmt::Debug, | ||
St2: fmt::Debug, | ||
State: fmt::Debug, | ||
{ | ||
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
f.debug_struct("SelectWithStrategy") | ||
.field("stream1", &self.stream1) | ||
.field("stream2", &self.stream2) | ||
.field("state", &self.state) | ||
.finish() | ||
} | ||
} |
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Is this a typo for close?
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
It's the generic representing the closure. So not a typo. Of course another name can be chosen. I don't really care about what it's called.