<!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 `/home/eli/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.0.1/src/macros/try_join.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>try_join.rs - source</title><link rel="stylesheet" type="text/css" href="../../../normalize.css"><link rel="stylesheet" type="text/css" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../../light.css" id="themeStyle"><link rel="stylesheet" type="text/css" href="../../../dark.css" disabled ><link rel="stylesheet" type="text/css" href="../../../ayu.css" disabled ><script id="default-settings"></script><script src="../../../storage.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="icon" type="image/svg+xml" 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id="crate-search"><option value="All crates">All crates</option></select><input class="search-input" name="search" disabled autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"></div><span class="help-button">?</span> <a id="settings-menu" href="../../../settings.html"><img src="../../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><pre class="line-numbers"><span id="1"> 1</span> <span id="2"> 2</span> <span id="3"> 3</span> <span id="4"> 4</span> <span id="5"> 5</span> <span id="6"> 6</span> <span id="7"> 7</span> <span id="8"> 8</span> <span id="9"> 9</span> <span id="10"> 10</span> <span id="11"> 11</span> <span id="12"> 12</span> <span id="13"> 13</span> <span id="14"> 14</span> <span id="15"> 15</span> <span id="16"> 16</span> <span id="17"> 17</span> <span id="18"> 18</span> <span id="19"> 19</span> <span id="20"> 20</span> <span id="21"> 21</span> <span 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complete with `Ok(_)` or on the first `Err(_)`.</span> <span class="doccomment">///</span> <span class="doccomment">/// The `try_join!` macro must be used inside of async functions, closures, and</span> <span class="doccomment">/// blocks.</span> <span class="doccomment">///</span> <span class="doccomment">/// Similar to [`join!`], the `try_join!` macro takes a list of async</span> <span class="doccomment">/// expressions and evaluates them concurrently on the same task. Each async</span> <span class="doccomment">/// expression evaluates to a future and the futures from each expression are</span> <span class="doccomment">/// multiplexed on the current task. The `try_join!` macro returns when **all**</span> <span class="doccomment">/// branches return with `Ok` or when the **first** branch returns with `Err`.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`join!`]: macro@join</span> <span class="doccomment">///</span> <span class="doccomment">/// # Notes</span> <span class="doccomment">///</span> <span class="doccomment">/// The supplied futures are stored inline and does not require allocating a</span> <span class="doccomment">/// `Vec`.</span> <span class="doccomment">///</span> <span class="doccomment">/// ### Runtime characteristics</span> <span class="doccomment">///</span> <span class="doccomment">/// By running all async expressions on the current task, the expressions are</span> <span class="doccomment">/// able to run **concurrently** but not in **parallel**. This means all</span> <span class="doccomment">/// expressions are run on the same thread and if one branch blocks the thread,</span> <span class="doccomment">/// all other expressions will be unable to continue. If parallelism is</span> <span class="doccomment">/// required, spawn each async expression using [`tokio::spawn`] and pass the</span> <span class="doccomment">/// join handle to `try_join!`.</span> <span class="doccomment">///</span> <span class="doccomment">/// [`tokio::spawn`]: crate::spawn</span> <span class="doccomment">///</span> <span class="doccomment">/// # Examples</span> <span class="doccomment">///</span> <span class="doccomment">/// Basic try_join with two branches.</span> <span class="doccomment">///</span> <span class="doccomment">/// ```</span> <span class="doccomment">/// async fn do_stuff_async() -> Result<(), &'static str> {</span> <span class="doccomment">/// // async work</span> <span class="doccomment">/// # Ok(())</span> <span class="doccomment">/// }</span> <span class="doccomment">///</span> <span class="doccomment">/// async fn more_async_work() -> Result<(), &'static str> {</span> <span class="doccomment">/// // more here</span> <span class="doccomment">/// # Ok(())</span> <span class="doccomment">/// }</span> <span class="doccomment">///</span> <span class="doccomment">/// #[tokio::main]</span> <span class="doccomment">/// async fn main() {</span> <span class="doccomment">/// let res = tokio::try_join!(</span> <span class="doccomment">/// do_stuff_async(),</span> <span class="doccomment">/// more_async_work());</span> <span class="doccomment">///</span> <span class="doccomment">/// match res {</span> <span class="doccomment">/// Ok((first, second)) => {</span> <span class="doccomment">/// // do something with the values</span> <span class="doccomment">/// }</span> <span class="doccomment">/// Err(err) => {</span> <span class="doccomment">/// println!("processing failed; error = {}", err);</span> <span class="doccomment">/// }</span> <span class="doccomment">/// }</span> <span class="doccomment">/// }</span> <span class="doccomment">/// ```</span> <span class="attribute">#[<span class="ident">macro_export</span>]</span> <span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">docsrs</span>, <span class="ident">doc</span>(<span class="ident">cfg</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"macros"</span>)))]</span> <span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">try_join</span> { (@ { <span class="comment">// One `_` for each branch in the `try_join!` macro. This is not used once</span> <span class="comment">// normalization is complete.</span> ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">count</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="comment">// Normalized try_join! branches</span> $( ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">skip</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>, )<span class="op">*</span> }) <span class="op">=</span><span class="op">></span> {{ <span class="kw">use</span> <span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro-nonterminal">macros</span>::<span class="ident">support</span>::{<span class="ident">maybe_done</span>, <span class="ident">poll_fn</span>, <span class="ident">Future</span>, <span class="ident">Pin</span>}; <span class="kw">use</span> <span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro-nonterminal">macros</span>::<span class="ident">support</span>::<span class="ident">Poll</span>::{<span class="ident">Ready</span>, <span class="ident">Pending</span>}; <span class="comment">// Safety: nothing must be moved out of `futures`. This is to satisfy</span> <span class="comment">// the requirement of `Pin::new_unchecked` called below.</span> <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">futures</span> <span class="op">=</span> ( $( <span class="ident">maybe_done</span>(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>), )<span class="op">*</span> ); <span class="ident">poll_fn</span>(<span class="kw">move</span> <span class="op">|</span><span class="ident">cx</span><span class="op">|</span> { <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">is_pending</span> <span class="op">=</span> <span class="bool-val">false</span>; $( <span class="comment">// Extract the future for this branch from the tuple.</span> <span class="kw">let</span> ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">skip</span>,)<span class="op">*</span> <span class="ident">fut</span>, .. ) <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">futures</span>; <span class="comment">// Safety: future is stored on the stack above</span> <span class="comment">// and never moved.</span> <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">fut</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">Pin</span>::<span class="ident">new_unchecked</span>(<span class="ident">fut</span>) }; <span class="comment">// Try polling</span> <span class="kw">if</span> <span class="ident">fut</span>.<span class="ident">as_mut</span>().<span class="ident">poll</span>(<span class="ident">cx</span>).<span class="ident">is_pending</span>() { <span class="ident">is_pending</span> <span class="op">=</span> <span class="bool-val">true</span>; } <span class="kw">else</span> <span class="kw">if</span> <span class="ident">fut</span>.<span class="ident">as_mut</span>().<span class="ident">output_mut</span>().<span class="ident">expect</span>(<span class="string">"expected completed future"</span>).<span class="ident">is_err</span>() { <span class="kw">return</span> <span class="ident">Ready</span>(<span class="prelude-val">Err</span>(<span class="ident">fut</span>.<span class="ident">take_output</span>().<span class="ident">expect</span>(<span class="string">"expected completed future"</span>).<span class="ident">err</span>().<span class="ident">unwrap</span>())) } )<span class="op">*</span> <span class="kw">if</span> <span class="ident">is_pending</span> { <span class="ident">Pending</span> } <span class="kw">else</span> { <span class="ident">Ready</span>(<span class="prelude-val">Ok</span>(($({ <span class="comment">// Extract the future for this branch from the tuple.</span> <span class="kw">let</span> ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">skip</span>,)<span class="op">*</span> <span class="ident">fut</span>, .. ) <span class="op">=</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">futures</span>; <span class="comment">// Safety: future is stored on the stack above</span> <span class="comment">// and never moved.</span> <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">fut</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">Pin</span>::<span class="ident">new_unchecked</span>(<span class="ident">fut</span>) }; <span class="ident">fut</span> .<span class="ident">take_output</span>() .<span class="ident">expect</span>(<span class="string">"expected completed future"</span>) .<span class="ident">ok</span>() .<span class="ident">expect</span>(<span class="string">"expected Ok(_)"</span>) },)<span class="kw-2">*</span>))) } }).<span class="ident">await</span> }}; <span class="comment">// ===== Normalize =====</span> (@ { ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>:<span class="ident">tt</span>)<span class="op">*</span> ) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>:<span class="ident">tt</span>)<span class="op">*</span> } <span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>, $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>:<span class="ident">tt</span>)<span class="op">*</span> ) <span class="op">=</span><span class="op">></span> { <span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro">try_join</span><span class="macro">!</span>(@{ ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>)<span class="op">*</span> <span class="kw">_</span>) $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">t</span>)<span class="op">*</span> ($(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">s</span>)<span class="kw-2">*</span>) <span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>, } $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">r</span>)<span class="kw-2">*</span>) }; <span class="comment">// ===== Entry point =====</span> ( $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>:<span class="ident">expr</span>),<span class="op">*</span> $(,)<span class="question-mark">?</span>) <span class="op">=</span><span class="op">></span> { <span class="macro-nonterminal">$</span><span class="kw">crate</span>::<span class="macro">try_join</span><span class="macro">!</span>(@{ () } $(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">e</span>,)<span class="kw-2">*</span>) }; } </pre></div> </section><section id="search" class="content hidden"></section><section class="footer"></section><script>window.rootPath = "../../../";window.currentCrate = "tokio";</script><script src="../../../main.js"></script><script src="../../../source-script.js"></script><script src="../../../source-files.js"></script><script defer src="../../../search-index.js"></script></body></html>