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</pre><div class="example-wrap"><pre class="rust ">
<span class="doccomment">//! Asynchronous values.</span>
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">cell</span>::<span class="ident">Cell</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">marker</span>::<span class="ident">Unpin</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">pin</span>::<span class="ident">Pin</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">option</span>::<span class="prelude-ty">Option</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">ptr</span>::<span class="ident">NonNull</span>;
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">task</span>::{<span class="ident">Context</span>, <span class="ident">Poll</span>};
<span class="kw">use</span> <span class="ident">core</span>::<span class="ident">ops</span>::{<span class="ident">Drop</span>, <span class="ident">Generator</span>, <span class="ident">GeneratorState</span>};
<span class="attribute">#[<span class="ident">doc</span>(<span class="ident">inline</span>)]</span>
<span class="kw">pub</span> <span class="kw">use</span> <span class="ident">core</span>::<span class="ident">future</span>::<span class="kw-2">*</span>;
<span class="doccomment">/// Wrap a generator in a future.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function returns a `GenFuture` underneath, but hides it in `impl Trait` to give</span>
<span class="doccomment">/// better error messages (`impl Future` rather than `GenFuture<[closure.....]>`).</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"gen_future"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"50547"</span>)]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">from_generator</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Generator</span><span class="op"><</span><span class="ident">Yield</span> <span class="op">=</span> ()<span class="op">>></span>(<span class="ident">x</span>: <span class="ident">T</span>) <span class="op">-></span> <span class="kw">impl</span> <span class="ident">Future</span><span class="op"><</span><span class="ident">Output</span> <span class="op">=</span> <span class="ident">T</span>::<span class="ident">Return</span><span class="op">></span> {
<span class="ident">GenFuture</span>(<span class="ident">x</span>)
}
<span class="doccomment">/// A wrapper around generators used to implement `Future` for `async`/`await` code.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"gen_future"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"50547"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">Eq</span>, <span class="ident">PartialEq</span>, <span class="ident">Ord</span>, <span class="ident">PartialOrd</span>, <span class="ident">Hash</span>)]</span>
<span class="kw">struct</span> <span class="ident">GenFuture</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Generator</span><span class="op"><</span><span class="ident">Yield</span> <span class="op">=</span> ()<span class="op">>></span>(<span class="ident">T</span>);
<span class="comment">// We rely on the fact that async/await futures are immovable in order to create</span>
<span class="comment">// self-referential borrows in the underlying generator.</span>
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Generator</span><span class="op"><</span><span class="ident">Yield</span> <span class="op">=</span> ()<span class="op">>></span> <span class="op">!</span><span class="ident">Unpin</span> <span class="kw">for</span> <span class="ident">GenFuture</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"gen_future"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"50547"</span>)]</span>
<span class="kw">impl</span><span class="op"><</span><span class="ident">T</span>: <span class="ident">Generator</span><span class="op"><</span><span class="ident">Yield</span> <span class="op">=</span> ()<span class="op">>></span> <span class="ident">Future</span> <span class="kw">for</span> <span class="ident">GenFuture</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Output</span> <span class="op">=</span> <span class="ident">T</span>::<span class="ident">Return</span>;
<span class="kw">fn</span> <span class="ident">poll</span>(<span class="self">self</span>: <span class="ident">Pin</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">Self</span><span class="op">></span>, <span class="ident">cx</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Context</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="self">Self</span>::<span class="ident">Output</span><span class="op">></span> {
<span class="comment">// Safe because we're !Unpin + !Drop mapping to a ?Unpin value</span>
<span class="kw">let</span> <span class="ident">gen</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="ident">Pin</span>::<span class="ident">map_unchecked_mut</span>(<span class="self">self</span>, <span class="op">|</span><span class="ident">s</span><span class="op">|</span> <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">s</span>.<span class="number">0</span>) };
<span class="ident">set_task_context</span>(<span class="ident">cx</span>, <span class="op">||</span> <span class="kw">match</span> <span class="ident">gen</span>.<span class="ident">resume</span>() {
<span class="ident">GeneratorState</span>::<span class="ident">Yielded</span>(()) <span class="op">=></span> <span class="ident">Poll</span>::<span class="ident">Pending</span>,
<span class="ident">GeneratorState</span>::<span class="ident">Complete</span>(<span class="ident">x</span>) <span class="op">=></span> <span class="ident">Poll</span>::<span class="ident">Ready</span>(<span class="ident">x</span>),
})
}
}
<span class="macro">thread_local</span><span class="macro">!</span> {
<span class="kw">static</span> <span class="ident">TLS_CX</span>: <span class="ident">Cell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">Context</span><span class="op"><</span><span class="lifetime">'static</span><span class="op">>></span><span class="op">>></span> <span class="op">=</span> <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>);
}
<span class="kw">struct</span> <span class="ident">SetOnDrop</span>(<span class="prelude-ty">Option</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">Context</span><span class="op"><</span><span class="lifetime">'static</span><span class="op">>></span><span class="op">></span>);
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">SetOnDrop</span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="ident">TLS_CX</span>.<span class="ident">with</span>(<span class="op">|</span><span class="ident">tls_cx</span><span class="op">|</span> {
<span class="ident">tls_cx</span>.<span class="ident">set</span>(<span class="self">self</span>.<span class="number">0</span>.<span class="ident">take</span>());
});
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"gen_future"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"50547"</span>)]</span>
<span class="doccomment">/// Sets the thread-local task context used by async/await futures.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">set_task_context</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="ident">cx</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Context</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>, <span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">R</span>
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>() <span class="op">-></span> <span class="ident">R</span>
{
<span class="comment">// transmute the context's lifetime to 'static so we can store it.</span>
<span class="kw">let</span> <span class="ident">cx</span> <span class="op">=</span> <span class="kw">unsafe</span> {
<span class="ident">core</span>::<span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Context</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>, <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Context</span><span class="op"><</span><span class="lifetime">'static</span><span class="op">>></span>(<span class="ident">cx</span>)
};
<span class="kw">let</span> <span class="ident">old_cx</span> <span class="op">=</span> <span class="ident">TLS_CX</span>.<span class="ident">with</span>(<span class="op">|</span><span class="ident">tls_cx</span><span class="op">|</span> {
<span class="ident">tls_cx</span>.<span class="ident">replace</span>(<span class="prelude-val">Some</span>(<span class="ident">NonNull</span>::<span class="ident">from</span>(<span class="ident">cx</span>)))
});
<span class="kw">let</span> <span class="ident">_reset</span> <span class="op">=</span> <span class="ident">SetOnDrop</span>(<span class="ident">old_cx</span>);
<span class="ident">f</span>()
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"gen_future"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"50547"</span>)]</span>
<span class="doccomment">/// Retrieves the thread-local task context used by async/await futures.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function acquires exclusive access to the task context.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Panics if no context has been set or if the context has already been</span>
<span class="doccomment">/// retrieved by a surrounding call to get_task_context.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">get_task_context</span><span class="op"><</span><span class="ident">F</span>, <span class="ident">R</span><span class="op">></span>(<span class="ident">f</span>: <span class="ident">F</span>) <span class="op">-></span> <span class="ident">R</span>
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">FnOnce</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">Context</span><span class="op"><</span><span class="lifetime">'_</span><span class="op">></span>) <span class="op">-></span> <span class="ident">R</span>
{
<span class="kw">let</span> <span class="ident">cx_ptr</span> <span class="op">=</span> <span class="ident">TLS_CX</span>.<span class="ident">with</span>(<span class="op">|</span><span class="ident">tls_cx</span><span class="op">|</span> {
<span class="comment">// Clear the entry so that nested `get_task_waker` calls</span>
<span class="comment">// will fail or set their own value.</span>
<span class="ident">tls_cx</span>.<span class="ident">replace</span>(<span class="prelude-val">None</span>)
});
<span class="kw">let</span> <span class="ident">_reset</span> <span class="op">=</span> <span class="ident">SetOnDrop</span>(<span class="ident">cx_ptr</span>);
<span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">cx_ptr</span> <span class="op">=</span> <span class="ident">cx_ptr</span>.<span class="ident">expect</span>(
<span class="string">"TLS Context not set. This is a rustc bug. \
Please file an issue on https://github.com/rust-lang/rust."</span>);
<span class="comment">// Safety: we've ensured exclusive access to the context by</span>
<span class="comment">// removing the pointer from TLS, only to be replaced once</span>
<span class="comment">// we're done with it.</span>
<span class="comment">//</span>
<span class="comment">// The pointer that was inserted came from an `&mut Context<'_>`,</span>
<span class="comment">// so it is safe to treat as mutable.</span>
<span class="kw">unsafe</span> { <span class="ident">f</span>(<span class="ident">cx_ptr</span>.<span class="ident">as_mut</span>()) }
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"gen_future"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"50547"</span>)]</span>
<span class="doccomment">/// Polls a future in the current thread-local task waker.</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">poll_with_tls_context</span><span class="op"><</span><span class="ident">F</span><span class="op">></span>(<span class="ident">f</span>: <span class="ident">Pin</span><span class="op"><</span><span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">F</span><span class="op">></span>) <span class="op">-></span> <span class="ident">Poll</span><span class="op"><</span><span class="ident">F</span>::<span class="ident">Output</span><span class="op">></span>
<span class="kw">where</span>
<span class="ident">F</span>: <span class="ident">Future</span>
{
<span class="ident">get_task_context</span>(<span class="op">|</span><span class="ident">cx</span><span class="op">|</span> <span class="ident">F</span>::<span class="ident">poll</span>(<span class="ident">f</span>, <span class="ident">cx</span>))
}
</pre></div>
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