| <!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/tokio-1.28.2/src/macros/pin.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>pin.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="../../../tokio/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="../../../tokio/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="doccomment">/// Pins a value on the stack. |
| /// |
| /// Calls to `async fn` return anonymous [`Future`] values that are `!Unpin`. |
| /// These values must be pinned before they can be polled. Calling `.await` will |
| /// handle this, but consumes the future. If it is required to call `.await` on |
| /// a `&mut _` reference, the caller is responsible for pinning the future. |
| /// |
| /// Pinning may be done by allocating with [`Box::pin`] or by using the stack |
| /// with the `pin!` macro. |
| /// |
| /// The following will **fail to compile**: |
| /// |
| /// ```compile_fail |
| /// async fn my_async_fn() { |
| /// // async logic here |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let mut future = my_async_fn(); |
| /// (&mut future).await; |
| /// } |
| /// ``` |
| /// |
| /// To make this work requires pinning: |
| /// |
| /// ``` |
| /// use tokio::pin; |
| /// |
| /// async fn my_async_fn() { |
| /// // async logic here |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let future = my_async_fn(); |
| /// pin!(future); |
| /// |
| /// (&mut future).await; |
| /// } |
| /// ``` |
| /// |
| /// Pinning is useful when using `select!` and stream operators that require `T: |
| /// Stream + Unpin`. |
| /// |
| /// [`Future`]: trait@std::future::Future |
| /// [`Box::pin`]: std::boxed::Box::pin |
| /// |
| /// # Usage |
| /// |
| /// The `pin!` macro takes **identifiers** as arguments. It does **not** work |
| /// with expressions. |
| /// |
| /// The following does not compile as an expression is passed to `pin!`. |
| /// |
| /// ```compile_fail |
| /// async fn my_async_fn() { |
| /// // async logic here |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let mut future = pin!(my_async_fn()); |
| /// (&mut future).await; |
| /// } |
| /// ``` |
| /// |
| /// # Examples |
| /// |
| /// Using with select: |
| /// |
| /// ``` |
| /// use tokio::{pin, select}; |
| /// use tokio_stream::{self as stream, StreamExt}; |
| /// |
| /// async fn my_async_fn() { |
| /// // async logic here |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let mut stream = stream::iter(vec![1, 2, 3, 4]); |
| /// |
| /// let future = my_async_fn(); |
| /// pin!(future); |
| /// |
| /// loop { |
| /// select! { |
| /// _ = &mut future => { |
| /// // Stop looping `future` will be polled after completion |
| /// break; |
| /// } |
| /// Some(val) = stream.next() => { |
| /// println!("got value = {}", val); |
| /// } |
| /// } |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// Because assigning to a variable followed by pinning is common, there is also |
| /// a variant of the macro that supports doing both in one go. |
| /// |
| /// ``` |
| /// use tokio::{pin, select}; |
| /// |
| /// async fn my_async_fn() { |
| /// // async logic here |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// pin! { |
| /// let future1 = my_async_fn(); |
| /// let future2 = my_async_fn(); |
| /// } |
| /// |
| /// select! { |
| /// _ = &mut future1 => {} |
| /// _ = &mut future2 => {} |
| /// } |
| /// } |
| /// ``` |
| </span><span class="attribute">#[macro_export] |
| </span><span class="macro">macro_rules! </span>pin { |
| ($(<span class="macro-nonterminal">$x</span>:ident),<span class="kw-2">*</span>) => { $( |
| <span class="comment">// Move the value to ensure that it is owned |
| </span><span class="kw">let </span><span class="kw-2">mut </span><span class="macro-nonterminal">$x </span>= <span class="macro-nonterminal">$x</span>; |
| <span class="comment">// Shadow the original binding so that it can't be directly accessed |
| // ever again. |
| </span><span class="attribute">#[allow(unused_mut)] |
| </span><span class="kw">let </span><span class="kw-2">mut </span><span class="macro-nonterminal">$x </span>= <span class="kw">unsafe </span>{ |
| <span class="macro-nonterminal">$crate::macros::support::Pin::new_unchecked</span>(<span class="kw-2">&mut </span><span class="macro-nonterminal">$x</span>) |
| }; |
| )* }; |
| ($( |
| <span class="kw">let </span><span class="macro-nonterminal">$x</span>:ident = <span class="macro-nonterminal">$init</span>:expr; |
| )<span class="kw-2">*</span>) => { |
| $( |
| <span class="kw">let </span><span class="macro-nonterminal">$x </span>= <span class="macro-nonterminal">$init</span>; |
| <span class="macro-nonterminal">$</span><span class="macro">crate::pin!</span>(<span class="macro-nonterminal">$x</span>); |
| )* |
| }; |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
