| <!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/try_join.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>try_join.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">/// Waits on multiple concurrent branches, returning when **all** branches |
| /// complete with `Ok(_)` or on the first `Err(_)`. |
| /// |
| /// The `try_join!` macro must be used inside of async functions, closures, and |
| /// blocks. |
| /// |
| /// Similar to [`join!`], the `try_join!` macro takes a list of async |
| /// expressions and evaluates them concurrently on the same task. Each async |
| /// expression evaluates to a future and the futures from each expression are |
| /// multiplexed on the current task. The `try_join!` macro returns when **all** |
| /// branches return with `Ok` or when the **first** branch returns with `Err`. |
| /// |
| /// [`join!`]: macro@join |
| /// |
| /// # Notes |
| /// |
| /// The supplied futures are stored inline and does not require allocating a |
| /// `Vec`. |
| /// |
| /// ### Runtime characteristics |
| /// |
| /// By running all async expressions on the current task, the expressions are |
| /// able to run **concurrently** but not in **parallel**. This means all |
| /// expressions are run on the same thread and if one branch blocks the thread, |
| /// all other expressions will be unable to continue. If parallelism is |
| /// required, spawn each async expression using [`tokio::spawn`] and pass the |
| /// join handle to `try_join!`. |
| /// |
| /// [`tokio::spawn`]: crate::spawn |
| /// |
| /// # Examples |
| /// |
| /// Basic try_join with two branches. |
| /// |
| /// ``` |
| /// async fn do_stuff_async() -> Result<(), &'static str> { |
| /// // async work |
| /// # Ok(()) |
| /// } |
| /// |
| /// async fn more_async_work() -> Result<(), &'static str> { |
| /// // more here |
| /// # Ok(()) |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let res = tokio::try_join!( |
| /// do_stuff_async(), |
| /// more_async_work()); |
| /// |
| /// match res { |
| /// Ok((first, second)) => { |
| /// // do something with the values |
| /// } |
| /// Err(err) => { |
| /// println!("processing failed; error = {}", err); |
| /// } |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// Using `try_join!` with spawned tasks. |
| /// |
| /// ``` |
| /// use tokio::task::JoinHandle; |
| /// |
| /// async fn do_stuff_async() -> Result<(), &'static str> { |
| /// // async work |
| /// # Err("failed") |
| /// } |
| /// |
| /// async fn more_async_work() -> Result<(), &'static str> { |
| /// // more here |
| /// # Ok(()) |
| /// } |
| /// |
| /// async fn flatten<T>(handle: JoinHandle<Result<T, &'static str>>) -> Result<T, &'static str> { |
| /// match handle.await { |
| /// Ok(Ok(result)) => Ok(result), |
| /// Ok(Err(err)) => Err(err), |
| /// Err(err) => Err("handling failed"), |
| /// } |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let handle1 = tokio::spawn(do_stuff_async()); |
| /// let handle2 = tokio::spawn(more_async_work()); |
| /// match tokio::try_join!(flatten(handle1), flatten(handle2)) { |
| /// Ok(val) => { |
| /// // do something with the values |
| /// } |
| /// Err(err) => { |
| /// println!("Failed with {}.", err); |
| /// # assert_eq!(err, "failed"); |
| /// } |
| /// } |
| /// } |
| /// ``` |
| </span><span class="attribute">#[macro_export] |
| #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">"macros"</span>)))] |
| </span><span class="macro">macro_rules! </span>try_join { |
| (@ { |
| <span class="comment">// One `_` for each branch in the `try_join!` macro. This is not used once |
| // normalization is complete. |
| </span>( $(<span class="macro-nonterminal">$count</span>:tt)* ) |
| |
| <span class="comment">// The expression `0+1+1+ ... +1` equal to the number of branches. |
| </span>( $(<span class="macro-nonterminal">$total</span>:tt)* ) |
| |
| <span class="comment">// Normalized try_join! branches |
| </span>$( ( $(<span class="macro-nonterminal">$skip</span>:tt)* ) <span class="macro-nonterminal">$e</span>:expr, )* |
| |
| }) => {{ |
| <span class="kw">use </span><span class="macro-nonterminal">$crate::macros::support</span>::{maybe_done, poll_fn, Future, Pin}; |
| <span class="kw">use </span><span class="macro-nonterminal">$crate::macros::support::Poll</span>::{Ready, Pending}; |
| |
| <span class="comment">// Safety: nothing must be moved out of `futures`. This is to satisfy |
| // the requirement of `Pin::new_unchecked` called below. |
| // |
| // We can't use the `pin!` macro for this because `futures` is a tuple |
| // and the standard library provides no way to pin-project to the fields |
| // of a tuple. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>futures = ( $( maybe_done(<span class="macro-nonterminal">$e</span>), )* ); |
| |
| <span class="comment">// This assignment makes sure that the `poll_fn` closure only has a |
| // reference to the futures, instead of taking ownership of them. This |
| // mitigates the issue described in |
| // <https://internals.rust-lang.org/t/surprising-soundness-trouble-around-pollfn/17484> |
| </span><span class="kw">let </span><span class="kw-2">mut </span>futures = <span class="kw-2">&mut </span>futures; |
| |
| <span class="comment">// Each time the future created by poll_fn is polled, a different future will be polled first |
| // to ensure every future passed to join! gets a chance to make progress even if |
| // one of the futures consumes the whole budget. |
| // |
| // This is number of futures that will be skipped in the first loop |
| // iteration the next time. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>skip_next_time: u32 = <span class="number">0</span>; |
| |
| poll_fn(<span class="kw">move </span>|cx| { |
| <span class="kw">const </span>COUNT: u32 = $(<span class="macro-nonterminal">$total</span>)<span class="kw-2">*</span>; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>is_pending = <span class="bool-val">false</span>; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>to_run = COUNT; |
| |
| <span class="comment">// The number of futures that will be skipped in the first loop iteration |
| </span><span class="kw">let </span><span class="kw-2">mut </span>skip = skip_next_time; |
| |
| skip_next_time = <span class="kw">if </span>skip + <span class="number">1 </span>== COUNT { <span class="number">0 </span>} <span class="kw">else </span>{ skip + <span class="number">1 </span>}; |
| |
| <span class="comment">// This loop runs twice and the first `skip` futures |
| // are not polled in the first iteration. |
| </span><span class="kw">loop </span>{ |
| $( |
| <span class="kw">if </span>skip == <span class="number">0 </span>{ |
| <span class="kw">if </span>to_run == <span class="number">0 </span>{ |
| <span class="comment">// Every future has been polled |
| </span><span class="kw">break</span>; |
| } |
| to_run -= <span class="number">1</span>; |
| |
| <span class="comment">// Extract the future for this branch from the tuple. |
| </span><span class="kw">let </span>( $(<span class="macro-nonterminal">$skip</span>,)* fut, .. ) = <span class="kw-2">&mut *</span>futures; |
| |
| <span class="comment">// Safety: future is stored on the stack above |
| // and never moved. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>fut = <span class="kw">unsafe </span>{ Pin::new_unchecked(fut) }; |
| |
| <span class="comment">// Try polling |
| </span><span class="kw">if </span>fut.as_mut().poll(cx).is_pending() { |
| is_pending = <span class="bool-val">true</span>; |
| } <span class="kw">else if </span>fut.as_mut().output_mut().expect(<span class="string">"expected completed future"</span>).is_err() { |
| <span class="kw">return </span>Ready(<span class="prelude-val">Err</span>(fut.take_output().expect(<span class="string">"expected completed future"</span>).err().unwrap())) |
| } |
| } <span class="kw">else </span>{ |
| <span class="comment">// Future skipped, one less future to skip in the next iteration |
| </span>skip -= <span class="number">1</span>; |
| } |
| )* |
| } |
| |
| <span class="kw">if </span>is_pending { |
| Pending |
| } <span class="kw">else </span>{ |
| Ready(<span class="prelude-val">Ok</span>(($({ |
| <span class="comment">// Extract the future for this branch from the tuple. |
| </span><span class="kw">let </span>( $(<span class="macro-nonterminal">$skip</span>,)* fut, .. ) = <span class="kw-2">&mut </span>futures; |
| |
| <span class="comment">// Safety: future is stored on the stack above |
| // and never moved. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>fut = <span class="kw">unsafe </span>{ Pin::new_unchecked(fut) }; |
| |
| fut |
| .take_output() |
| .expect(<span class="string">"expected completed future"</span>) |
| .ok() |
| .expect(<span class="string">"expected Ok(_)"</span>) |
| },)<span class="kw-2">*</span>))) |
| } |
| }).<span class="kw">await |
| </span>}}; |
| |
| <span class="comment">// ===== Normalize ===== |
| |
| </span>(@ { ( $(<span class="macro-nonterminal">$s</span>:tt)* ) ( $(<span class="macro-nonterminal">$n</span>:tt)* ) $(<span class="macro-nonterminal">$t</span>:tt)* } <span class="macro-nonterminal">$e</span>:expr, $(<span class="macro-nonterminal">$r</span>:tt)* ) => { |
| <span class="macro-nonterminal">$</span><span class="macro">crate::try_join!</span>(@{ ($(<span class="macro-nonterminal">$s</span>)* <span class="kw">_</span>) ($(<span class="macro-nonterminal">$n</span>)* + <span class="number">1</span>) $(<span class="macro-nonterminal">$t</span>)* ($(<span class="macro-nonterminal">$s</span>)<span class="kw-2">*</span>) <span class="macro-nonterminal">$e</span>, } $(<span class="macro-nonterminal">$r</span>)<span class="kw-2">*</span>) |
| }; |
| |
| <span class="comment">// ===== Entry point ===== |
| |
| </span>( $(<span class="macro-nonterminal">$e</span>:expr),+ $(,)<span class="question-mark">?</span>) => { |
| <span class="macro-nonterminal">$</span><span class="macro">crate::try_join!</span>(@{ () (<span class="number">0</span>) } $(<span class="macro-nonterminal">$e</span>,)<span class="kw-2">*</span>) |
| }; |
| |
| () => { <span class="kw">async </span>{ <span class="prelude-val">Ok</span>(()) }.<span class="kw">await </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> |
