| <!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-executor-0.3.28/src/enter.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>enter.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_executor/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_executor/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>std::cell::Cell; |
| <span class="kw">use </span>std::fmt; |
| |
| <span class="macro">thread_local!</span>(<span class="kw">static </span>ENTERED: Cell<bool> = Cell::new(<span class="bool-val">false</span>)); |
| |
| <span class="doccomment">/// Represents an executor context. |
| /// |
| /// For more details, see [`enter` documentation](enter()). |
| </span><span class="kw">pub struct </span>Enter { |
| _priv: (), |
| } |
| |
| <span class="doccomment">/// An error returned by `enter` if an execution scope has already been |
| /// entered. |
| </span><span class="kw">pub struct </span>EnterError { |
| _priv: (), |
| } |
| |
| <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>EnterError { |
| <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">"EnterError"</span>).finish() |
| } |
| } |
| |
| <span class="kw">impl </span>fmt::Display <span class="kw">for </span>EnterError { |
| <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 { |
| <span class="macro">write!</span>(f, <span class="string">"an execution scope has already been entered"</span>) |
| } |
| } |
| |
| <span class="kw">impl </span>std::error::Error <span class="kw">for </span>EnterError {} |
| |
| <span class="doccomment">/// Marks the current thread as being within the dynamic extent of an |
| /// executor. |
| /// |
| /// Executor implementations should call this function before beginning to |
| /// execute a task, and drop the returned [`Enter`](Enter) value after |
| /// completing task execution: |
| /// |
| /// ``` |
| /// use futures::executor::enter; |
| /// |
| /// let enter = enter().expect("..."); |
| /// /* run task */ |
| /// drop(enter); |
| /// ``` |
| /// |
| /// Doing so ensures that executors aren't |
| /// accidentally invoked in a nested fashion. |
| /// |
| /// # Error |
| /// |
| /// Returns an error if the current thread is already marked, in which case the |
| /// caller should panic with a tailored error message. |
| </span><span class="kw">pub fn </span>enter() -> <span class="prelude-ty">Result</span><Enter, EnterError> { |
| ENTERED.with(|c| { |
| <span class="kw">if </span>c.get() { |
| <span class="prelude-val">Err</span>(EnterError { _priv: () }) |
| } <span class="kw">else </span>{ |
| c.set(<span class="bool-val">true</span>); |
| |
| <span class="prelude-val">Ok</span>(Enter { _priv: () }) |
| } |
| }) |
| } |
| |
| <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>Enter { |
| <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">"Enter"</span>).finish() |
| } |
| } |
| |
| <span class="kw">impl </span>Drop <span class="kw">for </span>Enter { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| ENTERED.with(|c| { |
| <span class="macro">assert!</span>(c.get()); |
| c.set(<span class="bool-val">false</span>); |
| }); |
| } |
| } |
| </code></pre></div> |
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