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</pre><div class="example-wrap"><pre class="rust ">
<span class="doccomment">/// Wait on multiple concurrent branches, returning when **all** branches</span>
<span class="doccomment">/// 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>
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