| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/futures-util-0.3.28/src/stream/select_with_strategy.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>select_with_strategy.rs - source</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../../SourceCodePro-Semibold.ttf.woff2"><link rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="../../../source-script.js"></script><script defer src="../../../source-files.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc source"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><a class="sidebar-logo" href="../../../futures_util/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a></nav><main><div class="width-limiter"><nav class="sub"><a class="sub-logo-container" href="../../../futures_util/index.html"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></a><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="example-wrap"><pre class="src-line-numbers"><span id="1">1</span> |
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| </pre><pre class="rust"><code><span class="kw">use </span><span class="kw">super</span>::assert_stream; |
| <span class="kw">use </span>core::{fmt, pin::Pin}; |
| <span class="kw">use </span>futures_core::stream::{FusedStream, Stream}; |
| <span class="kw">use </span>futures_core::task::{Context, Poll}; |
| <span class="kw">use </span>pin_project_lite::pin_project; |
| |
| <span class="doccomment">/// Type to tell [`SelectWithStrategy`] which stream to poll next. |
| </span><span class="attribute">#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)] |
| </span><span class="kw">pub enum </span>PollNext { |
| <span class="doccomment">/// Poll the first stream. |
| </span>Left, |
| <span class="doccomment">/// Poll the second stream. |
| </span>Right, |
| } |
| |
| <span class="kw">impl </span>PollNext { |
| <span class="doccomment">/// Toggle the value and return the old one. |
| </span><span class="kw">pub fn </span>toggle(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="self">Self </span>{ |
| <span class="kw">let </span>old = <span class="kw-2">*</span><span class="self">self</span>; |
| <span class="kw-2">*</span><span class="self">self </span>= <span class="self">self</span>.other(); |
| old |
| } |
| |
| <span class="kw">fn </span>other(<span class="kw-2">&</span><span class="self">self</span>) -> PollNext { |
| <span class="kw">match </span><span class="self">self </span>{ |
| PollNext::Left => PollNext::Right, |
| PollNext::Right => PollNext::Left, |
| } |
| } |
| } |
| |
| <span class="kw">impl </span>Default <span class="kw">for </span>PollNext { |
| <span class="kw">fn </span>default() -> <span class="self">Self </span>{ |
| PollNext::Left |
| } |
| } |
| |
| <span class="kw">enum </span>InternalState { |
| Start, |
| LeftFinished, |
| RightFinished, |
| BothFinished, |
| } |
| |
| <span class="kw">impl </span>InternalState { |
| <span class="kw">fn </span>finish(<span class="kw-2">&mut </span><span class="self">self</span>, ps: PollNext) { |
| <span class="kw">match </span>(<span class="kw-2">&</span><span class="self">self</span>, ps) { |
| (InternalState::Start, PollNext::Left) => { |
| <span class="kw-2">*</span><span class="self">self </span>= InternalState::LeftFinished; |
| } |
| (InternalState::Start, PollNext::Right) => { |
| <span class="kw-2">*</span><span class="self">self </span>= InternalState::RightFinished; |
| } |
| (InternalState::LeftFinished, PollNext::Right) |
| | (InternalState::RightFinished, PollNext::Left) => { |
| <span class="kw-2">*</span><span class="self">self </span>= InternalState::BothFinished; |
| } |
| <span class="kw">_ </span>=> {} |
| } |
| } |
| } |
| |
| <span class="macro">pin_project! </span>{ |
| <span class="doccomment">/// Stream for the [`select_with_strategy()`] function. See function docs for details. |
| </span><span class="attribute">#[must_use = <span class="string">"streams do nothing unless polled"</span>] |
| #[project = SelectWithStrategyProj] |
| </span><span class="kw">pub struct </span>SelectWithStrategy<St1, St2, Clos, State> { |
| <span class="attribute">#[pin] |
| </span>stream1: St1, |
| <span class="attribute">#[pin] |
| </span>stream2: St2, |
| internal_state: InternalState, |
| state: State, |
| clos: Clos, |
| } |
| } |
| |
| <span class="doccomment">/// 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); |
| /// |
| /// 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); |
| /// } |
| /// # }); |
| /// ``` |
| </span><span class="kw">pub fn </span>select_with_strategy<St1, St2, Clos, State>( |
| stream1: St1, |
| stream2: St2, |
| which: Clos, |
| ) -> SelectWithStrategy<St1, St2, Clos, State> |
| <span class="kw">where |
| </span>St1: Stream, |
| St2: Stream<Item = St1::Item>, |
| Clos: FnMut(<span class="kw-2">&mut </span>State) -> PollNext, |
| State: Default, |
| { |
| assert_stream::<St1::Item, <span class="kw">_</span>>(SelectWithStrategy { |
| stream1, |
| stream2, |
| state: Default::default(), |
| internal_state: InternalState::Start, |
| clos: which, |
| }) |
| } |
| |
| <span class="kw">impl</span><St1, St2, Clos, State> SelectWithStrategy<St1, St2, Clos, State> { |
| <span class="doccomment">/// Acquires a reference to the underlying streams that this combinator is |
| /// pulling from. |
| </span><span class="kw">pub fn </span>get_ref(<span class="kw-2">&</span><span class="self">self</span>) -> (<span class="kw-2">&</span>St1, <span class="kw-2">&</span>St2) { |
| (<span class="kw-2">&</span><span class="self">self</span>.stream1, <span class="kw-2">&</span><span class="self">self</span>.stream2) |
| } |
| |
| <span class="doccomment">/// 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. |
| </span><span class="kw">pub fn </span>get_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> (<span class="kw-2">&mut </span>St1, <span class="kw-2">&mut </span>St2) { |
| (<span class="kw-2">&mut </span><span class="self">self</span>.stream1, <span class="kw-2">&mut </span><span class="self">self</span>.stream2) |
| } |
| |
| <span class="doccomment">/// 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. |
| </span><span class="kw">pub fn </span>get_pin_mut(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>) -> (Pin<<span class="kw-2">&mut </span>St1>, Pin<<span class="kw-2">&mut </span>St2>) { |
| <span class="kw">let </span>this = <span class="self">self</span>.project(); |
| (this.stream1, this.stream2) |
| } |
| |
| <span class="doccomment">/// 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. |
| </span><span class="kw">pub fn </span>into_inner(<span class="self">self</span>) -> (St1, St2) { |
| (<span class="self">self</span>.stream1, <span class="self">self</span>.stream2) |
| } |
| } |
| |
| <span class="kw">impl</span><St1, St2, Clos, State> FusedStream <span class="kw">for </span>SelectWithStrategy<St1, St2, Clos, State> |
| <span class="kw">where |
| </span>St1: Stream, |
| St2: Stream<Item = St1::Item>, |
| Clos: FnMut(<span class="kw-2">&mut </span>State) -> PollNext, |
| { |
| <span class="kw">fn </span>is_terminated(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">match </span><span class="self">self</span>.internal_state { |
| InternalState::BothFinished => <span class="bool-val">true</span>, |
| <span class="kw">_ </span>=> <span class="bool-val">false</span>, |
| } |
| } |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>poll_side<St1, St2, Clos, State>( |
| select: <span class="kw-2">&mut </span>SelectWithStrategyProj<<span class="lifetime">'_</span>, St1, St2, Clos, State>, |
| side: PollNext, |
| cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>, |
| ) -> Poll<<span class="prelude-ty">Option</span><St1::Item>> |
| <span class="kw">where |
| </span>St1: Stream, |
| St2: Stream<Item = St1::Item>, |
| { |
| <span class="kw">match </span>side { |
| PollNext::Left => select.stream1.as_mut().poll_next(cx), |
| PollNext::Right => select.stream2.as_mut().poll_next(cx), |
| } |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>poll_inner<St1, St2, Clos, State>( |
| select: <span class="kw-2">&mut </span>SelectWithStrategyProj<<span class="lifetime">'_</span>, St1, St2, Clos, State>, |
| side: PollNext, |
| cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>, |
| ) -> Poll<<span class="prelude-ty">Option</span><St1::Item>> |
| <span class="kw">where |
| </span>St1: Stream, |
| St2: Stream<Item = St1::Item>, |
| { |
| <span class="kw">let </span>first_done = <span class="kw">match </span>poll_side(select, side, cx) { |
| Poll::Ready(<span class="prelude-val">Some</span>(item)) => <span class="kw">return </span>Poll::Ready(<span class="prelude-val">Some</span>(item)), |
| Poll::Ready(<span class="prelude-val">None</span>) => { |
| select.internal_state.finish(side); |
| <span class="bool-val">true |
| </span>} |
| Poll::Pending => <span class="bool-val">false</span>, |
| }; |
| <span class="kw">let </span>other = side.other(); |
| <span class="kw">match </span>poll_side(select, other, cx) { |
| Poll::Ready(<span class="prelude-val">None</span>) => { |
| select.internal_state.finish(other); |
| <span class="kw">if </span>first_done { |
| Poll::Ready(<span class="prelude-val">None</span>) |
| } <span class="kw">else </span>{ |
| Poll::Pending |
| } |
| } |
| a => a, |
| } |
| } |
| |
| <span class="kw">impl</span><St1, St2, Clos, State> Stream <span class="kw">for </span>SelectWithStrategy<St1, St2, Clos, State> |
| <span class="kw">where |
| </span>St1: Stream, |
| St2: Stream<Item = St1::Item>, |
| Clos: FnMut(<span class="kw-2">&mut </span>State) -> PollNext, |
| { |
| <span class="kw">type </span>Item = St1::Item; |
| |
| <span class="kw">fn </span>poll_next(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="prelude-ty">Option</span><St1::Item>> { |
| <span class="kw">let </span><span class="kw-2">mut </span>this = <span class="self">self</span>.project(); |
| |
| <span class="kw">match </span>this.internal_state { |
| InternalState::Start => { |
| <span class="kw">let </span>next_side = (this.clos)(this.state); |
| poll_inner(<span class="kw-2">&mut </span>this, next_side, cx) |
| } |
| InternalState::LeftFinished => <span class="kw">match </span>this.stream2.poll_next(cx) { |
| Poll::Ready(<span class="prelude-val">None</span>) => { |
| <span class="kw-2">*</span>this.internal_state = InternalState::BothFinished; |
| Poll::Ready(<span class="prelude-val">None</span>) |
| } |
| a => a, |
| }, |
| InternalState::RightFinished => <span class="kw">match </span>this.stream1.poll_next(cx) { |
| Poll::Ready(<span class="prelude-val">None</span>) => { |
| <span class="kw-2">*</span>this.internal_state = InternalState::BothFinished; |
| Poll::Ready(<span class="prelude-val">None</span>) |
| } |
| a => a, |
| }, |
| InternalState::BothFinished => Poll::Ready(<span class="prelude-val">None</span>), |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><St1, St2, Clos, State> fmt::Debug <span class="kw">for </span>SelectWithStrategy<St1, St2, Clos, State> |
| <span class="kw">where |
| </span>St1: fmt::Debug, |
| St2: fmt::Debug, |
| State: fmt::Debug, |
| { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| f.debug_struct(<span class="string">"SelectWithStrategy"</span>) |
| .field(<span class="string">"stream1"</span>, <span class="kw-2">&</span><span class="self">self</span>.stream1) |
| .field(<span class="string">"stream2"</span>, <span class="kw-2">&</span><span class="self">self</span>.stream2) |
| .field(<span class="string">"state"</span>, <span class="kw-2">&</span><span class="self">self</span>.state) |
| .finish() |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="futures_util" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
