| <!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-util-0.7.8/src/sync/reusable_box.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>reusable_box.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_util/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_util/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::alloc::Layout; |
| <span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::future::Future; |
| <span class="kw">use </span>std::marker::PhantomData; |
| <span class="kw">use </span>std::mem::{<span class="self">self</span>, ManuallyDrop}; |
| <span class="kw">use </span>std::pin::Pin; |
| <span class="kw">use </span>std::ptr; |
| <span class="kw">use </span>std::task::{Context, Poll}; |
| |
| <span class="doccomment">/// A reusable `Pin<Box<dyn Future<Output = T> + Send + 'a>>`. |
| /// |
| /// This type lets you replace the future stored in the box without |
| /// reallocating when the size and alignment permits this. |
| </span><span class="kw">pub struct </span>ReusableBoxFuture<<span class="lifetime">'a</span>, T> { |
| boxed: Pin<Box<<span class="kw">dyn </span>Future<Output = T> + Send + <span class="lifetime">'a</span>>>, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, T> ReusableBoxFuture<<span class="lifetime">'a</span>, T> { |
| <span class="doccomment">/// Create a new `ReusableBoxFuture<T>` containing the provided future. |
| </span><span class="kw">pub fn </span>new<F>(future: F) -> <span class="self">Self |
| </span><span class="kw">where |
| </span>F: Future<Output = T> + Send + <span class="lifetime">'a</span>, |
| { |
| <span class="self">Self </span>{ |
| boxed: Box::pin(future), |
| } |
| } |
| |
| <span class="doccomment">/// Replace the future currently stored in this box. |
| /// |
| /// This reallocates if and only if the layout of the provided future is |
| /// different from the layout of the currently stored future. |
| </span><span class="kw">pub fn </span>set<F>(<span class="kw-2">&mut </span><span class="self">self</span>, future: F) |
| <span class="kw">where |
| </span>F: Future<Output = T> + Send + <span class="lifetime">'a</span>, |
| { |
| <span class="kw">if let </span><span class="prelude-val">Err</span>(future) = <span class="self">self</span>.try_set(future) { |
| <span class="kw-2">*</span><span class="self">self </span>= <span class="self">Self</span>::new(future); |
| } |
| } |
| |
| <span class="doccomment">/// Replace the future currently stored in this box. |
| /// |
| /// This function never reallocates, but returns an error if the provided |
| /// future has a different size or alignment from the currently stored |
| /// future. |
| </span><span class="kw">pub fn </span>try_set<F>(<span class="kw-2">&mut </span><span class="self">self</span>, future: F) -> <span class="prelude-ty">Result</span><(), F> |
| <span class="kw">where |
| </span>F: Future<Output = T> + Send + <span class="lifetime">'a</span>, |
| { |
| <span class="comment">// If we try to inline the contents of this function, the type checker complains because |
| // the bound `T: 'a` is not satisfied in the call to `pending()`. But by putting it in an |
| // inner function that doesn't have `T` as a generic parameter, we implicitly get the bound |
| // `F::Output: 'a` transitively through `F: 'a`, allowing us to call `pending()`. |
| </span><span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>real_try_set<<span class="lifetime">'a</span>, F>( |
| this: <span class="kw-2">&mut </span>ReusableBoxFuture<<span class="lifetime">'a</span>, F::Output>, |
| future: F, |
| ) -> <span class="prelude-ty">Result</span><(), F> |
| <span class="kw">where |
| </span>F: Future + Send + <span class="lifetime">'a</span>, |
| { |
| <span class="comment">// future::Pending<T> is a ZST so this never allocates. |
| </span><span class="kw">let </span>boxed = mem::replace(<span class="kw-2">&mut </span>this.boxed, Box::pin(Pending(PhantomData))); |
| reuse_pin_box(boxed, future, |boxed| this.boxed = Pin::from(boxed)) |
| } |
| |
| real_try_set(<span class="self">self</span>, future) |
| } |
| |
| <span class="doccomment">/// Get a pinned reference to the underlying future. |
| </span><span class="kw">pub fn </span>get_pin(<span class="kw-2">&mut </span><span class="self">self</span>) -> Pin<<span class="kw-2">&mut </span>(<span class="kw">dyn </span>Future<Output = T> + Send)> { |
| <span class="self">self</span>.boxed.as_mut() |
| } |
| |
| <span class="doccomment">/// Poll the future stored inside this box. |
| </span><span class="kw">pub fn </span>poll(<span class="kw-2">&mut </span><span class="self">self</span>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<T> { |
| <span class="self">self</span>.get_pin().poll(cx) |
| } |
| } |
| |
| <span class="kw">impl</span><T> Future <span class="kw">for </span>ReusableBoxFuture<<span class="lifetime">'_</span>, T> { |
| <span class="kw">type </span>Output = T; |
| |
| <span class="doccomment">/// Poll the future stored inside this box. |
| </span><span class="kw">fn </span>poll(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<T> { |
| Pin::into_inner(<span class="self">self</span>).get_pin().poll(cx) |
| } |
| } |
| |
| <span class="comment">// The only method called on self.boxed is poll, which takes &mut self, so this |
| // struct being Sync does not permit any invalid access to the Future, even if |
| // the future is not Sync. |
| </span><span class="kw">unsafe impl</span><T> Sync <span class="kw">for </span>ReusableBoxFuture<<span class="lifetime">'_</span>, T> {} |
| |
| <span class="kw">impl</span><T> fmt::Debug <span class="kw">for </span>ReusableBoxFuture<<span class="lifetime">'_</span>, T> { |
| <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">"ReusableBoxFuture"</span>).finish() |
| } |
| } |
| |
| <span class="kw">fn </span>reuse_pin_box<T: <span class="question-mark">?</span>Sized, U, O, F>(boxed: Pin<Box<T>>, new_value: U, callback: F) -> <span class="prelude-ty">Result</span><O, U> |
| <span class="kw">where |
| </span>F: FnOnce(Box<U>) -> O, |
| { |
| <span class="kw">let </span>layout = Layout::for_value::<T>(<span class="kw-2">&*</span>boxed); |
| <span class="kw">if </span>layout != Layout::new::<U>() { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(new_value); |
| } |
| |
| <span class="comment">// SAFETY: We don't ever construct a non-pinned reference to the old `T` from now on, and we |
| // always drop the `T`. |
| </span><span class="kw">let </span>raw: <span class="kw-2">*mut </span>T = Box::into_raw(<span class="kw">unsafe </span>{ Pin::into_inner_unchecked(boxed) }); |
| |
| <span class="comment">// When dropping the old value panics, we still want to call `callback` — so move the rest of |
| // the code into a guard type. |
| </span><span class="kw">let </span>guard = CallOnDrop::new(|| { |
| <span class="kw">let </span>raw: <span class="kw-2">*mut </span>U = raw.cast::<U>(); |
| <span class="kw">unsafe </span>{ raw.write(new_value) }; |
| |
| <span class="comment">// SAFETY: |
| // - `T` and `U` have the same layout. |
| // - `raw` comes from a `Box` that uses the same allocator as this one. |
| // - `raw` points to a valid instance of `U` (we just wrote it in). |
| </span><span class="kw">let </span>boxed = <span class="kw">unsafe </span>{ Box::from_raw(raw) }; |
| |
| callback(boxed) |
| }); |
| |
| <span class="comment">// Drop the old value. |
| </span><span class="kw">unsafe </span>{ ptr::drop_in_place(raw) }; |
| |
| <span class="comment">// Run the rest of the code. |
| </span><span class="prelude-val">Ok</span>(guard.call()) |
| } |
| |
| <span class="kw">struct </span>CallOnDrop<O, F: FnOnce() -> O> { |
| f: ManuallyDrop<F>, |
| } |
| |
| <span class="kw">impl</span><O, F: FnOnce() -> O> CallOnDrop<O, F> { |
| <span class="kw">fn </span>new(f: F) -> <span class="self">Self </span>{ |
| <span class="kw">let </span>f = ManuallyDrop::new(f); |
| <span class="self">Self </span>{ f } |
| } |
| <span class="kw">fn </span>call(<span class="self">self</span>) -> O { |
| <span class="kw">let </span><span class="kw-2">mut </span>this = ManuallyDrop::new(<span class="self">self</span>); |
| <span class="kw">let </span>f = <span class="kw">unsafe </span>{ ManuallyDrop::take(<span class="kw-2">&mut </span>this.f) }; |
| f() |
| } |
| } |
| |
| <span class="kw">impl</span><O, F: FnOnce() -> O> Drop <span class="kw">for </span>CallOnDrop<O, F> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">let </span>f = <span class="kw">unsafe </span>{ ManuallyDrop::take(<span class="kw-2">&mut </span><span class="self">self</span>.f) }; |
| f(); |
| } |
| } |
| |
| <span class="doccomment">/// The same as `std::future::Pending<T>`; we can't use that type directly because on rustc |
| /// versions <1.60 it didn't unconditionally implement `Send`. |
| </span><span class="comment">// FIXME: use `std::future::Pending<T>` once the MSRV is >=1.60 |
| </span><span class="kw">struct </span>Pending<T>(PhantomData<<span class="kw">fn</span>() -> T>); |
| |
| <span class="kw">impl</span><T> Future <span class="kw">for </span>Pending<T> { |
| <span class="kw">type </span>Output = T; |
| |
| <span class="kw">fn </span>poll(<span class="self">self</span>: Pin<<span class="kw-2">&mut </span><span class="self">Self</span>>, _cx: <span class="kw-2">&mut </span>Context<<span class="lifetime">'_</span>>) -> Poll<<span class="self">Self</span>::Output> { |
| Poll::Pending |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="tokio_util" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
