| <!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/git/checkouts/tokio-377c595163f99a10/dfe252d/tokio/src/future/poll_fn.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>poll_fn.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="attribute">#![allow(dead_code)] |
| |
| </span><span class="doccomment">//! Definition of the `PollFn` adapter combinator. |
| |
| </span><span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::future::Future; |
| <span class="kw">use </span>std::pin::Pin; |
| <span class="kw">use </span>std::task::{Context, Poll}; |
| |
| <span class="comment">// This struct is intentionally `!Unpin` when `F` is `!Unpin`. This is to |
| // mitigate the issue where rust puts noalias on mutable references to the |
| // `PollFn` type if it is `Unpin`. If the closure has ownership of a future, |
| // then this "leaks" and the future is affected by noalias too, which we don't |
| // want. |
| // |
| // See this thread for more information: |
| // <https://internals.rust-lang.org/t/surprising-soundness-trouble-around-pollfn/17484> |
| // |
| // The fact that `PollFn` is not `Unpin` when it shouldn't be is tested in |
| // `tests/async_send_sync.rs`. |
| |
| </span><span class="doccomment">/// Future for the [`poll_fn`] function. |
| </span><span class="kw">pub struct </span>PollFn<F> { |
| f: F, |
| } |
| |
| <span class="doccomment">/// Creates a new future wrapping around a function returning [`Poll`]. |
| </span><span class="kw">pub fn </span>poll_fn<T, F>(f: F) -> PollFn<F> |
| <span class="kw">where |
| </span>F: FnMut(<span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<T>, |
| { |
| PollFn { f } |
| } |
| |
| <span class="kw">impl</span><F> fmt::Debug <span class="kw">for </span>PollFn<F> { |
| <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">"PollFn"</span>).finish() |
| } |
| } |
| |
| <span class="kw">impl</span><T, F> Future <span class="kw">for </span>PollFn<F> |
| <span class="kw">where |
| </span>F: FnMut(<span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<T>, |
| { |
| <span class="kw">type </span>Output = T; |
| |
| <span class="kw">fn </span>poll(<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<T> { |
| <span class="comment">// Safety: We never construct a `Pin<&mut F>` anywhere, so accessing `f` |
| // mutably in an unpinned way is sound. |
| // |
| // This use of unsafe cannot be replaced with the pin-project macro |
| // because: |
| // * If we put `#[pin]` on the field, then it gives us a `Pin<&mut F>`, |
| // which we can't use to call the closure. |
| // * If we don't put `#[pin]` on the field, then it makes `PollFn` be |
| // unconditionally `Unpin`, which we also don't want. |
| </span><span class="kw">let </span>me = <span class="kw">unsafe </span>{ Pin::into_inner_unchecked(<span class="self">self</span>) }; |
| (me.f)(cx) |
| } |
| } |
| </code></pre></div> |
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