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 <!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/sync/oneshot.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>oneshot.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="attribute">#![cfg_attr(not(feature = <span class="string">&quot;sync&quot;</span>), allow(dead_code, unreachable_pub))]

 </span><span class="doccomment">//! A one-shot channel is used for sending a single message between
 //! asynchronous tasks. The [`channel`] function is used to create a
 //! [`Sender`] and [`Receiver`] handle pair that form the channel.
 //!
 //! The `Sender` handle is used by the producer to send the value.
 //! The `Receiver` handle is used by the consumer to receive the value.
 //!
 //! Each handle can be used on separate tasks.
 //!
 //! Since the `send` method is not async, it can be used anywhere. This includes
 //! sending between two runtimes, and using it from non-async code.
 //!
 //! If the [`Receiver`] is closed before receiving a message which has already
 //! been sent, the message will remain in the channel until the receiver is
 //! dropped, at which point the message will be dropped immediately.
 //!
 //! # Examples
 //!
 //! ```
 //! use tokio::sync::oneshot;
 //!
 //! #[tokio::main]
 //! async fn main() {
 //!     let (tx, rx) = oneshot::channel();
 //!
 //!     tokio::spawn(async move {
 //!         if let Err(_) = tx.send(3) {
 //!             println!(&quot;the receiver dropped&quot;);
 //!         }
 //!     });
 //!
 //!     match rx.await {
 //!         Ok(v) =&gt; println!(&quot;got = {:?}&quot;, v),
 //!         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 //!     }
 //! }
 //! ```
 //!
 //! If the sender is dropped without sending, the receiver will fail with
 //! [`error::RecvError`]:
 //!
 //! ```
 //! use tokio::sync::oneshot;
 //!
 //! #[tokio::main]
 //! async fn main() {
 //!     let (tx, rx) = oneshot::channel::&lt;u32&gt;();
 //!
 //!     tokio::spawn(async move {
 //!         drop(tx);
 //!     });
 //!
 //!     match rx.await {
 //!         Ok(_) =&gt; panic!(&quot;This doesn&#39;t happen&quot;),
 //!         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 //!     }
 //! }
 //! ```
 //!
 //! To use a oneshot channel in a `tokio::select!` loop, add `&amp;mut` in front of
 //! the channel.
 //!
 //! ```
 //! use tokio::sync::oneshot;
 //! use tokio::time::{interval, sleep, Duration};
 //!
 //! #[tokio::main]
 //! # async fn _doc() {}
 //! # #[tokio::main(flavor = &quot;current_thread&quot;, start_paused = true)]
 //! async fn main() {
 //!     let (send, mut recv) = oneshot::channel();
 //!     let mut interval = interval(Duration::from_millis(100));
 //!
 //!     # let handle =
 //!     tokio::spawn(async move {
 //!         sleep(Duration::from_secs(1)).await;
 //!         send.send(&quot;shut down&quot;).unwrap();
 //!     });
 //!
 //!     loop {
 //!         tokio::select! {
 //!             _ = interval.tick() =&gt; println!(&quot;Another 100ms&quot;),
 //!             msg = &amp;mut recv =&gt; {
 //!                 println!(&quot;Got message: {}&quot;, msg.unwrap());
 //!                 break;
 //!             }
 //!         }
 //!     }
 //!     # handle.await.unwrap();
 //! }
 //! ```
 //!
 //! To use a `Sender` from a destructor, put it in an [`Option`] and call
 //! [`Option::take`].
 //!
 //! ```
 //! use tokio::sync::oneshot;
 //!
 //! struct SendOnDrop {
 //!     sender: Option&lt;oneshot::Sender&lt;&amp;&#39;static str&gt;&gt;,
 //! }
 //! impl Drop for SendOnDrop {
 //!     fn drop(&amp;mut self) {
 //!         if let Some(sender) = self.sender.take() {
 //!             // Using `let _ =` to ignore send errors.
 //!             let _ = sender.send(&quot;I got dropped!&quot;);
 //!         }
 //!     }
 //! }
 //!
 //! #[tokio::main]
 //! # async fn _doc() {}
 //! # #[tokio::main(flavor = &quot;current_thread&quot;)]
 //! async fn main() {
 //!     let (send, recv) = oneshot::channel();
 //!
 //!     let send_on_drop = SendOnDrop { sender: Some(send) };
 //!     drop(send_on_drop);
 //!
 //!     assert_eq!(recv.await, Ok(&quot;I got dropped!&quot;));
 //! }
 //! ```

 </span><span class="kw">use </span><span class="kw">crate</span>::loom::cell::UnsafeCell;
 <span class="kw">use </span><span class="kw">crate</span>::loom::sync::atomic::AtomicUsize;
 <span class="kw">use </span><span class="kw">crate</span>::loom::sync::Arc;
 <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
 </span><span class="kw">use </span><span class="kw">crate</span>::util::trace;

 <span class="kw">use </span>std::fmt;
 <span class="kw">use </span>std::future::Future;
 <span class="kw">use </span>std::mem::MaybeUninit;
 <span class="kw">use </span>std::pin::Pin;
 <span class="kw">use </span>std::sync::atomic::Ordering::{<span class="self">self</span>, AcqRel, Acquire};
 <span class="kw">use </span>std::task::Poll::{Pending, Ready};
 <span class="kw">use </span>std::task::{Context, Poll, Waker};

 <span class="doccomment">/// Sends a value to the associated [`Receiver`].
 ///
 /// A pair of both a [`Sender`] and a [`Receiver`]  are created by the
 /// [`channel`](fn@channel) function.
 ///
 /// # Examples
 ///
 /// ```
 /// use tokio::sync::oneshot;
 ///
 /// #[tokio::main]
 /// async fn main() {
 ///     let (tx, rx) = oneshot::channel();
 ///
 ///     tokio::spawn(async move {
 ///         if let Err(_) = tx.send(3) {
 ///             println!(&quot;the receiver dropped&quot;);
 ///         }
 ///     });
 ///
 ///     match rx.await {
 ///         Ok(v) =&gt; println!(&quot;got = {:?}&quot;, v),
 ///         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 ///     }
 /// }
 /// ```
 ///
 /// If the sender is dropped without sending, the receiver will fail with
 /// [`error::RecvError`]:
 ///
 /// ```
 /// use tokio::sync::oneshot;
 ///
 /// #[tokio::main]
 /// async fn main() {
 ///     let (tx, rx) = oneshot::channel::&lt;u32&gt;();
 ///
 ///     tokio::spawn(async move {
 ///         drop(tx);
 ///     });
 ///
 ///     match rx.await {
 ///         Ok(_) =&gt; panic!(&quot;This doesn&#39;t happen&quot;),
 ///         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 ///     }
 /// }
 /// ```
 ///
 /// To use a `Sender` from a destructor, put it in an [`Option`] and call
 /// [`Option::take`].
 ///
 /// ```
 /// use tokio::sync::oneshot;
 ///
 /// struct SendOnDrop {
 ///     sender: Option&lt;oneshot::Sender&lt;&amp;&#39;static str&gt;&gt;,
 /// }
 /// impl Drop for SendOnDrop {
 ///     fn drop(&amp;mut self) {
 ///         if let Some(sender) = self.sender.take() {
 ///             // Using `let _ =` to ignore send errors.
 ///             let _ = sender.send(&quot;I got dropped!&quot;);
 ///         }
 ///     }
 /// }
 ///
 /// #[tokio::main]
 /// # async fn _doc() {}
 /// # #[tokio::main(flavor = &quot;current_thread&quot;)]
 /// async fn main() {
 ///     let (send, recv) = oneshot::channel();
 ///
 ///     let send_on_drop = SendOnDrop { sender: Some(send) };
 ///     drop(send_on_drop);
 ///
 ///     assert_eq!(recv.await, Ok(&quot;I got dropped!&quot;));
 /// }
 /// ```
 ///
 /// [`Option`]: std::option::Option
 /// [`Option::take`]: std::option::Option::take
 </span><span class="attribute">#[derive(Debug)]
 </span><span class="kw">pub struct </span>Sender&lt;T&gt; {
     inner: <span class="prelude-ty">Option</span>&lt;Arc&lt;Inner&lt;T&gt;&gt;&gt;,
     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span>resource_span: tracing::Span,
 }

 <span class="doccomment">/// Receives a value from the associated [`Sender`].
 ///
 /// A pair of both a [`Sender`] and a [`Receiver`]  are created by the
 /// [`channel`](fn@channel) function.
 ///
 /// This channel has no `recv` method because the receiver itself implements the
 /// [`Future`] trait. To receive a `Result&lt;T, `[`error::RecvError`]`&gt;`, `.await` the `Receiver` object directly.
 ///
 /// The `poll` method on the `Future` trait is allowed to spuriously return
 /// `Poll::Pending` even if the message has been sent. If such a spurious
 /// failure happens, then the caller will be woken when the spurious failure has
 /// been resolved so that the caller can attempt to receive the message again.
 /// Note that receiving such a wakeup does not guarantee that the next call will
 /// succeed — it could fail with another spurious failure. (A spurious failure
 /// does not mean that the message is lost. It is just delayed.)
 ///
 /// [`Future`]: trait@std::future::Future
 ///
 /// # Examples
 ///
 /// ```
 /// use tokio::sync::oneshot;
 ///
 /// #[tokio::main]
 /// async fn main() {
 ///     let (tx, rx) = oneshot::channel();
 ///
 ///     tokio::spawn(async move {
 ///         if let Err(_) = tx.send(3) {
 ///             println!(&quot;the receiver dropped&quot;);
 ///         }
 ///     });
 ///
 ///     match rx.await {
 ///         Ok(v) =&gt; println!(&quot;got = {:?}&quot;, v),
 ///         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 ///     }
 /// }
 /// ```
 ///
 /// If the sender is dropped without sending, the receiver will fail with
 /// [`error::RecvError`]:
 ///
 /// ```
 /// use tokio::sync::oneshot;
 ///
 /// #[tokio::main]
 /// async fn main() {
 ///     let (tx, rx) = oneshot::channel::&lt;u32&gt;();
 ///
 ///     tokio::spawn(async move {
 ///         drop(tx);
 ///     });
 ///
 ///     match rx.await {
 ///         Ok(_) =&gt; panic!(&quot;This doesn&#39;t happen&quot;),
 ///         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 ///     }
 /// }
 /// ```
 ///
 /// To use a `Receiver` in a `tokio::select!` loop, add `&amp;mut` in front of the
 /// channel.
 ///
 /// ```
 /// use tokio::sync::oneshot;
 /// use tokio::time::{interval, sleep, Duration};
 ///
 /// #[tokio::main]
 /// # async fn _doc() {}
 /// # #[tokio::main(flavor = &quot;current_thread&quot;, start_paused = true)]
 /// async fn main() {
 ///     let (send, mut recv) = oneshot::channel();
 ///     let mut interval = interval(Duration::from_millis(100));
 ///
 ///     # let handle =
 ///     tokio::spawn(async move {
 ///         sleep(Duration::from_secs(1)).await;
 ///         send.send(&quot;shut down&quot;).unwrap();
 ///     });
 ///
 ///     loop {
 ///         tokio::select! {
 ///             _ = interval.tick() =&gt; println!(&quot;Another 100ms&quot;),
 ///             msg = &amp;mut recv =&gt; {
 ///                 println!(&quot;Got message: {}&quot;, msg.unwrap());
 ///                 break;
 ///             }
 ///         }
 ///     }
 ///     # handle.await.unwrap();
 /// }
 /// ```
 </span><span class="attribute">#[derive(Debug)]
 </span><span class="kw">pub struct </span>Receiver&lt;T&gt; {
     inner: <span class="prelude-ty">Option</span>&lt;Arc&lt;Inner&lt;T&gt;&gt;&gt;,
     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span>resource_span: tracing::Span,
     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span>async_op_span: tracing::Span,
     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span>async_op_poll_span: tracing::Span,
 }

 <span class="kw">pub mod </span>error {
     <span class="doccomment">//! Oneshot error types.

     </span><span class="kw">use </span>std::fmt;

     <span class="doccomment">/// Error returned by the `Future` implementation for `Receiver`.
     ///
     /// This error is returned by the receiver when the sender is dropped without sending.
     </span><span class="attribute">#[derive(Debug, Eq, PartialEq, Clone)]
     </span><span class="kw">pub struct </span>RecvError(<span class="kw">pub</span>(<span class="kw">super</span>) ());

     <span class="doccomment">/// Error returned by the `try_recv` function on `Receiver`.
     </span><span class="attribute">#[derive(Debug, Eq, PartialEq, Clone)]
     </span><span class="kw">pub enum </span>TryRecvError {
         <span class="doccomment">/// The send half of the channel has not yet sent a value.
         </span>Empty,

         <span class="doccomment">/// The send half of the channel was dropped without sending a value.
         </span>Closed,
     }

     <span class="comment">// ===== impl RecvError =====

     </span><span class="kw">impl </span>fmt::Display <span class="kw">for </span>RecvError {
         <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, fmt: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
             <span class="macro">write!</span>(fmt, <span class="string">&quot;channel closed&quot;</span>)
         }
     }

     <span class="kw">impl </span>std::error::Error <span class="kw">for </span>RecvError {}

     <span class="comment">// ===== impl TryRecvError =====

     </span><span class="kw">impl </span>fmt::Display <span class="kw">for </span>TryRecvError {
         <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, fmt: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
             <span class="kw">match </span><span class="self">self </span>{
                 TryRecvError::Empty =&gt; <span class="macro">write!</span>(fmt, <span class="string">&quot;channel empty&quot;</span>),
                 TryRecvError::Closed =&gt; <span class="macro">write!</span>(fmt, <span class="string">&quot;channel closed&quot;</span>),
             }
         }
     }

     <span class="kw">impl </span>std::error::Error <span class="kw">for </span>TryRecvError {}
 }

 <span class="kw">use </span><span class="self">self</span>::error::<span class="kw-2">*</span>;

 <span class="kw">struct </span>Inner&lt;T&gt; {
     <span class="doccomment">/// Manages the state of the inner cell.
     </span>state: AtomicUsize,

     <span class="doccomment">/// The value. This is set by `Sender` and read by `Receiver`. The state of
     /// the cell is tracked by `state`.
     </span>value: UnsafeCell&lt;<span class="prelude-ty">Option</span>&lt;T&gt;&gt;,

     <span class="doccomment">/// The task to notify when the receiver drops without consuming the value.
     ///
     /// ## Safety
     ///
     /// The `TX_TASK_SET` bit in the `state` field is set if this field is
     /// initialized. If that bit is unset, this field may be uninitialized.
     </span>tx_task: Task,

     <span class="doccomment">/// The task to notify when the value is sent.
     ///
     /// ## Safety
     ///
     /// The `RX_TASK_SET` bit in the `state` field is set if this field is
     /// initialized. If that bit is unset, this field may be uninitialized.
     </span>rx_task: Task,
 }

 <span class="kw">struct </span>Task(UnsafeCell&lt;MaybeUninit&lt;Waker&gt;&gt;);

 <span class="kw">impl </span>Task {
     <span class="kw">unsafe fn </span>will_wake(<span class="kw-2">&amp;</span><span class="self">self</span>, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; bool {
         <span class="self">self</span>.with_task(|w| w.will_wake(cx.waker()))
     }

     <span class="kw">unsafe fn </span>with_task&lt;F, R&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, f: F) -&gt; R
     <span class="kw">where
         </span>F: FnOnce(<span class="kw-2">&amp;</span>Waker) -&gt; R,
     {
         <span class="self">self</span>.<span class="number">0</span>.with(|ptr| {
             <span class="kw">let </span>waker: <span class="kw-2">*const </span>Waker = (<span class="kw-2">*</span>ptr).as_ptr();
             f(<span class="kw-2">&amp;*</span>waker)
         })
     }

     <span class="kw">unsafe fn </span>drop_task(<span class="kw-2">&amp;</span><span class="self">self</span>) {
         <span class="self">self</span>.<span class="number">0</span>.with_mut(|ptr| {
             <span class="kw">let </span>ptr: <span class="kw-2">*mut </span>Waker = (<span class="kw-2">*</span>ptr).as_mut_ptr();
             ptr.drop_in_place();
         });
     }

     <span class="kw">unsafe fn </span>set_task(<span class="kw-2">&amp;</span><span class="self">self</span>, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) {
         <span class="self">self</span>.<span class="number">0</span>.with_mut(|ptr| {
             <span class="kw">let </span>ptr: <span class="kw-2">*mut </span>Waker = (<span class="kw-2">*</span>ptr).as_mut_ptr();
             ptr.write(cx.waker().clone());
         });
     }
 }

 <span class="attribute">#[derive(Clone, Copy)]
 </span><span class="kw">struct </span>State(usize);

 <span class="doccomment">/// Creates a new one-shot channel for sending single values across asynchronous
 /// tasks.
 ///
 /// The function returns separate &quot;send&quot; and &quot;receive&quot; handles. The `Sender`
 /// handle is used by the producer to send the value. The `Receiver` handle is
 /// used by the consumer to receive the value.
 ///
 /// Each handle can be used on separate tasks.
 ///
 /// # Examples
 ///
 /// ```
 /// use tokio::sync::oneshot;
 ///
 /// #[tokio::main]
 /// async fn main() {
 ///     let (tx, rx) = oneshot::channel();
 ///
 ///     tokio::spawn(async move {
 ///         if let Err(_) = tx.send(3) {
 ///             println!(&quot;the receiver dropped&quot;);
 ///         }
 ///     });
 ///
 ///     match rx.await {
 ///         Ok(v) =&gt; println!(&quot;got = {:?}&quot;, v),
 ///         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
 ///     }
 /// }
 /// ```
 </span><span class="attribute">#[track_caller]
 </span><span class="kw">pub fn </span>channel&lt;T&gt;() -&gt; (Sender&lt;T&gt;, Receiver&lt;T&gt;) {
     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span><span class="kw">let </span>resource_span = {
         <span class="kw">let </span>location = std::panic::Location::caller();

         <span class="kw">let </span>resource_span = <span class="macro">tracing::trace_span!</span>(
             <span class="string">&quot;runtime.resource&quot;</span>,
             concrete_type = <span class="string">&quot;Sender|Receiver&quot;</span>,
             kind = <span class="string">&quot;Sync&quot;</span>,
             loc.file = location.file(),
             loc.line = location.line(),
             loc.col = location.column(),
         );

         resource_span.in_scope(|| {
             <span class="macro">tracing::trace!</span>(
             target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
             tx_dropped = <span class="bool-val">false</span>,
             tx_dropped.op = <span class="string">&quot;override&quot;</span>,
             )
         });

         resource_span.in_scope(|| {
             <span class="macro">tracing::trace!</span>(
             target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
             rx_dropped = <span class="bool-val">false</span>,
             rx_dropped.op = <span class="string">&quot;override&quot;</span>,
             )
         });

         resource_span.in_scope(|| {
             <span class="macro">tracing::trace!</span>(
             target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
             value_sent = <span class="bool-val">false</span>,
             value_sent.op = <span class="string">&quot;override&quot;</span>,
             )
         });

         resource_span.in_scope(|| {
             <span class="macro">tracing::trace!</span>(
             target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
             value_received = <span class="bool-val">false</span>,
             value_received.op = <span class="string">&quot;override&quot;</span>,
             )
         });

         resource_span
     };

     <span class="kw">let </span>inner = Arc::new(Inner {
         state: AtomicUsize::new(State::new().as_usize()),
         value: UnsafeCell::new(<span class="prelude-val">None</span>),
         tx_task: Task(UnsafeCell::new(MaybeUninit::uninit())),
         rx_task: Task(UnsafeCell::new(MaybeUninit::uninit())),
     });

     <span class="kw">let </span>tx = Sender {
         inner: <span class="prelude-val">Some</span>(inner.clone()),
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span>resource_span: resource_span.clone(),
     };

     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span><span class="kw">let </span>async_op_span = resource_span
         .in_scope(|| <span class="macro">tracing::trace_span!</span>(<span class="string">&quot;runtime.resource.async_op&quot;</span>, source = <span class="string">&quot;Receiver::await&quot;</span>));

     <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
     </span><span class="kw">let </span>async_op_poll_span =
         async_op_span.in_scope(|| <span class="macro">tracing::trace_span!</span>(<span class="string">&quot;runtime.resource.async_op.poll&quot;</span>));

     <span class="kw">let </span>rx = Receiver {
         inner: <span class="prelude-val">Some</span>(inner),
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span>resource_span,
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span>async_op_span,
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span>async_op_poll_span,
     };

     (tx, rx)
 }

 <span class="kw">impl</span>&lt;T&gt; Sender&lt;T&gt; {
     <span class="doccomment">/// Attempts to send a value on this channel, returning it back if it could
     /// not be sent.
     ///
     /// This method consumes `self` as only one value may ever be sent on a oneshot
     /// channel. It is not marked async because sending a message to an oneshot
     /// channel never requires any form of waiting.  Because of this, the `send`
     /// method can be used in both synchronous and asynchronous code without
     /// problems.
     ///
     /// A successful send occurs when it is determined that the other end of the
     /// channel has not hung up already. An unsuccessful send would be one where
     /// the corresponding receiver has already been deallocated. Note that a
     /// return value of `Err` means that the data will never be received, but
     /// a return value of `Ok` does *not* mean that the data will be received.
     /// It is possible for the corresponding receiver to hang up immediately
     /// after this function returns `Ok`.
     ///
     /// # Examples
     ///
     /// Send a value to another task
     ///
     /// ```
     /// use tokio::sync::oneshot;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, rx) = oneshot::channel();
     ///
     ///     tokio::spawn(async move {
     ///         if let Err(_) = tx.send(3) {
     ///             println!(&quot;the receiver dropped&quot;);
     ///         }
     ///     });
     ///
     ///     match rx.await {
     ///         Ok(v) =&gt; println!(&quot;got = {:?}&quot;, v),
     ///         Err(_) =&gt; println!(&quot;the sender dropped&quot;),
     ///     }
     /// }
     /// ```
     </span><span class="kw">pub fn </span>send(<span class="kw-2">mut </span><span class="self">self</span>, t: T) -&gt; <span class="prelude-ty">Result</span>&lt;(), T&gt; {
         <span class="kw">let </span>inner = <span class="self">self</span>.inner.take().unwrap();

         inner.value.with_mut(|ptr| <span class="kw">unsafe </span>{
             <span class="comment">// SAFETY: The receiver will not access the `UnsafeCell` unless the
             // channel has been marked as &quot;complete&quot; (the `VALUE_SENT` state bit
             // is set).
             // That bit is only set by the sender later on in this method, and
             // calling this method consumes `self`. Therefore, if it was possible to
             // call this method, we know that the `VALUE_SENT` bit is unset, and
             // the receiver is not currently accessing the `UnsafeCell`.
             </span><span class="kw-2">*</span>ptr = <span class="prelude-val">Some</span>(t);
         });

         <span class="kw">if </span>!inner.complete() {
             <span class="kw">unsafe </span>{
                 <span class="comment">// SAFETY: The receiver will not access the `UnsafeCell` unless
                 // the channel has been marked as &quot;complete&quot;. Calling
                 // `complete()` will return true if this bit is set, and false
                 // if it is not set. Thus, if `complete()` returned false, it is
                 // safe for us to access the value, because we know that the
                 // receiver will not.
                 </span><span class="kw">return </span><span class="prelude-val">Err</span>(inner.consume_value().unwrap());
             }
         }

         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span><span class="self">self</span>.resource_span.in_scope(|| {
             <span class="macro">tracing::trace!</span>(
             target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
             value_sent = <span class="bool-val">true</span>,
             value_sent.op = <span class="string">&quot;override&quot;</span>,
             )
         });

         <span class="prelude-val">Ok</span>(())
     }

     <span class="doccomment">/// Waits for the associated [`Receiver`] handle to close.
     ///
     /// A [`Receiver`] is closed by either calling [`close`] explicitly or the
     /// [`Receiver`] value is dropped.
     ///
     /// This function is useful when paired with `select!` to abort a
     /// computation when the receiver is no longer interested in the result.
     ///
     /// # Return
     ///
     /// Returns a `Future` which must be awaited on.
     ///
     /// [`Receiver`]: Receiver
     /// [`close`]: Receiver::close
     ///
     /// # Examples
     ///
     /// Basic usage
     ///
     /// ```
     /// use tokio::sync::oneshot;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (mut tx, rx) = oneshot::channel::&lt;()&gt;();
     ///
     ///     tokio::spawn(async move {
     ///         drop(rx);
     ///     });
     ///
     ///     tx.closed().await;
     ///     println!(&quot;the receiver dropped&quot;);
     /// }
     /// ```
     ///
     /// Paired with select
     ///
     /// ```
     /// use tokio::sync::oneshot;
     /// use tokio::time::{self, Duration};
     ///
     /// async fn compute() -&gt; String {
     ///     // Complex computation returning a `String`
     /// # &quot;hello&quot;.to_string()
     /// }
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (mut tx, rx) = oneshot::channel();
     ///
     ///     tokio::spawn(async move {
     ///         tokio::select! {
     ///             _ = tx.closed() =&gt; {
     ///                 // The receiver dropped, no need to do any further work
     ///             }
     ///             value = compute() =&gt; {
     ///                 // The send can fail if the channel was closed at the exact same
     ///                 // time as when compute() finished, so just ignore the failure.
     ///                 let _ = tx.send(value);
     ///             }
     ///         }
     ///     });
     ///
     ///     // Wait for up to 10 seconds
     ///     let _ = time::timeout(Duration::from_secs(10), rx).await;
     /// }
     /// ```
     </span><span class="kw">pub async fn </span>closed(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="kw">use </span><span class="kw">crate</span>::future::poll_fn;

         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span><span class="kw">let </span>resource_span = <span class="self">self</span>.resource_span.clone();
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span><span class="kw">let </span>closed = trace::async_op(
             || poll_fn(|cx| <span class="self">self</span>.poll_closed(cx)),
             resource_span,
             <span class="string">&quot;Sender::closed&quot;</span>,
             <span class="string">&quot;poll_closed&quot;</span>,
             <span class="bool-val">false</span>,
         );
         <span class="attribute">#[cfg(not(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>)))]
         </span><span class="kw">let </span>closed = poll_fn(|cx| <span class="self">self</span>.poll_closed(cx));

         closed.<span class="kw">await
     </span>}

     <span class="doccomment">/// Returns `true` if the associated [`Receiver`] handle has been dropped.
     ///
     /// A [`Receiver`] is closed by either calling [`close`] explicitly or the
     /// [`Receiver`] value is dropped.
     ///
     /// If `true` is returned, a call to `send` will always result in an error.
     ///
     /// [`Receiver`]: Receiver
     /// [`close`]: Receiver::close
     ///
     /// # Examples
     ///
     /// ```
     /// use tokio::sync::oneshot;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, rx) = oneshot::channel();
     ///
     ///     assert!(!tx.is_closed());
     ///
     ///     drop(rx);
     ///
     ///     assert!(tx.is_closed());
     ///     assert!(tx.send(&quot;never received&quot;).is_err());
     /// }
     /// ```
     </span><span class="kw">pub fn </span>is_closed(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
         <span class="kw">let </span>inner = <span class="self">self</span>.inner.as_ref().unwrap();

         <span class="kw">let </span>state = State::load(<span class="kw-2">&amp;</span>inner.state, Acquire);
         state.is_closed()
     }

     <span class="doccomment">/// Checks whether the oneshot channel has been closed, and if not, schedules the
     /// `Waker` in the provided `Context` to receive a notification when the channel is
     /// closed.
     ///
     /// A [`Receiver`] is closed by either calling [`close`] explicitly, or when the
     /// [`Receiver`] value is dropped.
     ///
     /// Note that on multiple calls to poll, only the `Waker` from the `Context` passed
     /// to the most recent call will be scheduled to receive a wakeup.
     ///
     /// [`Receiver`]: struct@crate::sync::oneshot::Receiver
     /// [`close`]: fn@crate::sync::oneshot::Receiver::close
     ///
     /// # Return value
     ///
     /// This function returns:
     ///
     ///  * `Poll::Pending` if the channel is still open.
     ///  * `Poll::Ready(())` if the channel is closed.
     ///
     /// # Examples
     ///
     /// ```
     /// use tokio::sync::oneshot;
     ///
     /// use futures::future::poll_fn;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (mut tx, mut rx) = oneshot::channel::&lt;()&gt;();
     ///
     ///     tokio::spawn(async move {
     ///         rx.close();
     ///     });
     ///
     ///     poll_fn(|cx| tx.poll_closed(cx)).await;
     ///
     ///     println!(&quot;the receiver dropped&quot;);
     /// }
     /// ```
     </span><span class="kw">pub fn </span>poll_closed(<span class="kw-2">&amp;mut </span><span class="self">self</span>, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;()&gt; {
         <span class="comment">// Keep track of task budget
         </span><span class="kw">let </span>coop = <span class="macro">ready!</span>(<span class="kw">crate</span>::runtime::coop::poll_proceed(cx));

         <span class="kw">let </span>inner = <span class="self">self</span>.inner.as_ref().unwrap();

         <span class="kw">let </span><span class="kw-2">mut </span>state = State::load(<span class="kw-2">&amp;</span>inner.state, Acquire);

         <span class="kw">if </span>state.is_closed() {
             coop.made_progress();
             <span class="kw">return </span>Poll::Ready(());
         }

         <span class="kw">if </span>state.is_tx_task_set() {
             <span class="kw">let </span>will_notify = <span class="kw">unsafe </span>{ inner.tx_task.will_wake(cx) };

             <span class="kw">if </span>!will_notify {
                 state = State::unset_tx_task(<span class="kw-2">&amp;</span>inner.state);

                 <span class="kw">if </span>state.is_closed() {
                     <span class="comment">// Set the flag again so that the waker is released in drop
                     </span>State::set_tx_task(<span class="kw-2">&amp;</span>inner.state);
                     coop.made_progress();
                     <span class="kw">return </span>Ready(());
                 } <span class="kw">else </span>{
                     <span class="kw">unsafe </span>{ inner.tx_task.drop_task() };
                 }
             }
         }

         <span class="kw">if </span>!state.is_tx_task_set() {
             <span class="comment">// Attempt to set the task
             </span><span class="kw">unsafe </span>{
                 inner.tx_task.set_task(cx);
             }

             <span class="comment">// Update the state
             </span>state = State::set_tx_task(<span class="kw-2">&amp;</span>inner.state);

             <span class="kw">if </span>state.is_closed() {
                 coop.made_progress();
                 <span class="kw">return </span>Ready(());
             }
         }

         Pending
     }
 }

 <span class="kw">impl</span>&lt;T&gt; Drop <span class="kw">for </span>Sender&lt;T&gt; {
     <span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(inner) = <span class="self">self</span>.inner.as_ref() {
             inner.complete();
             <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
             </span><span class="self">self</span>.resource_span.in_scope(|| {
                 <span class="macro">tracing::trace!</span>(
                 target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
                 tx_dropped = <span class="bool-val">true</span>,
                 tx_dropped.op = <span class="string">&quot;override&quot;</span>,
                 )
             });
         }
     }
 }

 <span class="kw">impl</span>&lt;T&gt; Receiver&lt;T&gt; {
     <span class="doccomment">/// Prevents the associated [`Sender`] handle from sending a value.
     ///
     /// Any `send` operation which happens after calling `close` is guaranteed
     /// to fail. After calling `close`, [`try_recv`] should be called to
     /// receive a value if one was sent **before** the call to `close`
     /// completed.
     ///
     /// This function is useful to perform a graceful shutdown and ensure that a
     /// value will not be sent into the channel and never received.
     ///
     /// `close` is no-op if a message is already received or the channel
     /// is already closed.
     ///
     /// [`Sender`]: Sender
     /// [`try_recv`]: Receiver::try_recv
     ///
     /// # Examples
     ///
     /// Prevent a value from being sent
     ///
     /// ```
     /// use tokio::sync::oneshot;
     /// use tokio::sync::oneshot::error::TryRecvError;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, mut rx) = oneshot::channel();
     ///
     ///     assert!(!tx.is_closed());
     ///
     ///     rx.close();
     ///
     ///     assert!(tx.is_closed());
     ///     assert!(tx.send(&quot;never received&quot;).is_err());
     ///
     ///     match rx.try_recv() {
     ///         Err(TryRecvError::Closed) =&gt; {}
     ///         _ =&gt; unreachable!(),
     ///     }
     /// }
     /// ```
     ///
     /// Receive a value sent **before** calling `close`
     ///
     /// ```
     /// use tokio::sync::oneshot;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, mut rx) = oneshot::channel();
     ///
     ///     assert!(tx.send(&quot;will receive&quot;).is_ok());
     ///
     ///     rx.close();
     ///
     ///     let msg = rx.try_recv().unwrap();
     ///     assert_eq!(msg, &quot;will receive&quot;);
     /// }
     /// ```
     </span><span class="kw">pub fn </span>close(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(inner) = <span class="self">self</span>.inner.as_ref() {
             inner.close();
             <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
             </span><span class="self">self</span>.resource_span.in_scope(|| {
                 <span class="macro">tracing::trace!</span>(
                 target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
                 rx_dropped = <span class="bool-val">true</span>,
                 rx_dropped.op = <span class="string">&quot;override&quot;</span>,
                 )
             });
         }
     }

     <span class="doccomment">/// Attempts to receive a value.
     ///
     /// If a pending value exists in the channel, it is returned. If no value
     /// has been sent, the current task **will not** be registered for
     /// future notification.
     ///
     /// This function is useful to call from outside the context of an
     /// asynchronous task.
     ///
     /// Note that unlike the `poll` method, the `try_recv` method cannot fail
     /// spuriously. Any send or close event that happens before this call to
     /// `try_recv` will be correctly returned to the caller.
     ///
     /// # Return
     ///
     /// - `Ok(T)` if a value is pending in the channel.
     /// - `Err(TryRecvError::Empty)` if no value has been sent yet.
     /// - `Err(TryRecvError::Closed)` if the sender has dropped without sending
     ///   a value, or if the message has already been received.
     ///
     /// # Examples
     ///
     /// `try_recv` before a value is sent, then after.
     ///
     /// ```
     /// use tokio::sync::oneshot;
     /// use tokio::sync::oneshot::error::TryRecvError;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, mut rx) = oneshot::channel();
     ///
     ///     match rx.try_recv() {
     ///         // The channel is currently empty
     ///         Err(TryRecvError::Empty) =&gt; {}
     ///         _ =&gt; unreachable!(),
     ///     }
     ///
     ///     // Send a value
     ///     tx.send(&quot;hello&quot;).unwrap();
     ///
     ///     match rx.try_recv() {
     ///         Ok(value) =&gt; assert_eq!(value, &quot;hello&quot;),
     ///         _ =&gt; unreachable!(),
     ///     }
     /// }
     /// ```
     ///
     /// `try_recv` when the sender dropped before sending a value
     ///
     /// ```
     /// use tokio::sync::oneshot;
     /// use tokio::sync::oneshot::error::TryRecvError;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, mut rx) = oneshot::channel::&lt;()&gt;();
     ///
     ///     drop(tx);
     ///
     ///     match rx.try_recv() {
     ///         // The channel will never receive a value.
     ///         Err(TryRecvError::Closed) =&gt; {}
     ///         _ =&gt; unreachable!(),
     ///     }
     /// }
     /// ```
     </span><span class="kw">pub fn </span>try_recv(<span class="kw-2">&amp;mut </span><span class="self">self</span>) -&gt; <span class="prelude-ty">Result</span>&lt;T, TryRecvError&gt; {
         <span class="kw">let </span>result = <span class="kw">if let </span><span class="prelude-val">Some</span>(inner) = <span class="self">self</span>.inner.as_ref() {
             <span class="kw">let </span>state = State::load(<span class="kw-2">&amp;</span>inner.state, Acquire);

             <span class="kw">if </span>state.is_complete() {
                 <span class="comment">// SAFETY: If `state.is_complete()` returns true, then the
                 // `VALUE_SENT` bit has been set and the sender side of the
                 // channel will no longer attempt to access the inner
                 // `UnsafeCell`. Therefore, it is now safe for us to access the
                 // cell.
                 </span><span class="kw">match unsafe </span>{ inner.consume_value() } {
                     <span class="prelude-val">Some</span>(value) =&gt; {
                         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
                         </span><span class="self">self</span>.resource_span.in_scope(|| {
                             <span class="macro">tracing::trace!</span>(
                             target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
                             value_received = <span class="bool-val">true</span>,
                             value_received.op = <span class="string">&quot;override&quot;</span>,
                             )
                         });
                         <span class="prelude-val">Ok</span>(value)
                     }
                     <span class="prelude-val">None </span>=&gt; <span class="prelude-val">Err</span>(TryRecvError::Closed),
                 }
             } <span class="kw">else if </span>state.is_closed() {
                 <span class="prelude-val">Err</span>(TryRecvError::Closed)
             } <span class="kw">else </span>{
                 <span class="comment">// Not ready, this does not clear `inner`
                 </span><span class="kw">return </span><span class="prelude-val">Err</span>(TryRecvError::Empty);
             }
         } <span class="kw">else </span>{
             <span class="prelude-val">Err</span>(TryRecvError::Closed)
         };

         <span class="self">self</span>.inner = <span class="prelude-val">None</span>;
         result
     }

     <span class="doccomment">/// Blocking receive to call outside of asynchronous contexts.
     ///
     /// # Panics
     ///
     /// This function panics if called within an asynchronous execution
     /// context.
     ///
     /// # Examples
     ///
     /// ```
     /// use std::thread;
     /// use tokio::sync::oneshot;
     ///
     /// #[tokio::main]
     /// async fn main() {
     ///     let (tx, rx) = oneshot::channel::&lt;u8&gt;();
     ///
     ///     let sync_code = thread::spawn(move || {
     ///         assert_eq!(Ok(10), rx.blocking_recv());
     ///     });
     ///
     ///     let _ = tx.send(10);
     ///     sync_code.join().unwrap();
     /// }
     /// ```
     </span><span class="attribute">#[track_caller]
     #[cfg(feature = <span class="string">&quot;sync&quot;</span>)]
     #[cfg_attr(docsrs, doc(alias = <span class="string">&quot;recv_blocking&quot;</span>))]
     </span><span class="kw">pub fn </span>blocking_recv(<span class="self">self</span>) -&gt; <span class="prelude-ty">Result</span>&lt;T, RecvError&gt; {
         <span class="kw">crate</span>::future::block_on(<span class="self">self</span>)
     }
 }

 <span class="kw">impl</span>&lt;T&gt; Drop <span class="kw">for </span>Receiver&lt;T&gt; {
     <span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="kw">if let </span><span class="prelude-val">Some</span>(inner) = <span class="self">self</span>.inner.as_ref() {
             inner.close();
             <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
             </span><span class="self">self</span>.resource_span.in_scope(|| {
                 <span class="macro">tracing::trace!</span>(
                 target: <span class="string">&quot;runtime::resource::state_update&quot;</span>,
                 rx_dropped = <span class="bool-val">true</span>,
                 rx_dropped.op = <span class="string">&quot;override&quot;</span>,
                 )
             });
         }
     }
 }

 <span class="kw">impl</span>&lt;T&gt; Future <span class="kw">for </span>Receiver&lt;T&gt; {
     <span class="kw">type </span>Output = <span class="prelude-ty">Result</span>&lt;T, RecvError&gt;;

     <span class="kw">fn </span>poll(<span class="kw-2">mut </span><span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="self">Self</span>::Output&gt; {
         <span class="comment">// If `inner` is `None`, then `poll()` has already completed.
         </span><span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span><span class="kw">let </span>_res_span = <span class="self">self</span>.resource_span.clone().entered();
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span><span class="kw">let </span>_ao_span = <span class="self">self</span>.async_op_span.clone().entered();
         <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
         </span><span class="kw">let </span>_ao_poll_span = <span class="self">self</span>.async_op_poll_span.clone().entered();

         <span class="kw">let </span>ret = <span class="kw">if let </span><span class="prelude-val">Some</span>(inner) = <span class="self">self</span>.as_ref().get_ref().inner.as_ref() {
             <span class="attribute">#[cfg(all(tokio_unstable, feature = <span class="string">&quot;tracing&quot;</span>))]
             </span><span class="kw">let </span>res = <span class="macro">ready!</span>(<span class="macro">trace_poll_op!</span>(<span class="string">&quot;poll_recv&quot;</span>, inner.poll_recv(cx)))<span class="question-mark">?</span>;

             <span class="attribute">#[cfg(any(not(tokio_unstable), not(feature = <span class="string">&quot;tracing&quot;</span>)))]
             </span><span class="kw">let </span>res = <span class="macro">ready!</span>(inner.poll_recv(cx))<span class="question-mark">?</span>;

             res
         } <span class="kw">else </span>{
             <span class="macro">panic!</span>(<span class="string">&quot;called after complete&quot;</span>);
         };

         <span class="self">self</span>.inner = <span class="prelude-val">None</span>;
         Ready(<span class="prelude-val">Ok</span>(ret))
     }
 }

 <span class="kw">impl</span>&lt;T&gt; Inner&lt;T&gt; {
     <span class="kw">fn </span>complete(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
         <span class="kw">let </span>prev = State::set_complete(<span class="kw-2">&amp;</span><span class="self">self</span>.state);

         <span class="kw">if </span>prev.is_closed() {
             <span class="kw">return </span><span class="bool-val">false</span>;
         }

         <span class="kw">if </span>prev.is_rx_task_set() {
             <span class="comment">// TODO: Consume waker?
             </span><span class="kw">unsafe </span>{
                 <span class="self">self</span>.rx_task.with_task(Waker::wake_by_ref);
             }
         }

         <span class="bool-val">true
     </span>}

     <span class="kw">fn </span>poll_recv(<span class="kw-2">&amp;</span><span class="self">self</span>, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="prelude-ty">Result</span>&lt;T, RecvError&gt;&gt; {
         <span class="comment">// Keep track of task budget
         </span><span class="kw">let </span>coop = <span class="macro">ready!</span>(<span class="kw">crate</span>::runtime::coop::poll_proceed(cx));

         <span class="comment">// Load the state
         </span><span class="kw">let </span><span class="kw-2">mut </span>state = State::load(<span class="kw-2">&amp;</span><span class="self">self</span>.state, Acquire);

         <span class="kw">if </span>state.is_complete() {
             coop.made_progress();
             <span class="kw">match unsafe </span>{ <span class="self">self</span>.consume_value() } {
                 <span class="prelude-val">Some</span>(value) =&gt; Ready(<span class="prelude-val">Ok</span>(value)),
                 <span class="prelude-val">None </span>=&gt; Ready(<span class="prelude-val">Err</span>(RecvError(()))),
             }
         } <span class="kw">else if </span>state.is_closed() {
             coop.made_progress();
             Ready(<span class="prelude-val">Err</span>(RecvError(())))
         } <span class="kw">else </span>{
             <span class="kw">if </span>state.is_rx_task_set() {
                 <span class="kw">let </span>will_notify = <span class="kw">unsafe </span>{ <span class="self">self</span>.rx_task.will_wake(cx) };

                 <span class="comment">// Check if the task is still the same
                 </span><span class="kw">if </span>!will_notify {
                     <span class="comment">// Unset the task
                     </span>state = State::unset_rx_task(<span class="kw-2">&amp;</span><span class="self">self</span>.state);
                     <span class="kw">if </span>state.is_complete() {
                         <span class="comment">// Set the flag again so that the waker is released in drop
                         </span>State::set_rx_task(<span class="kw-2">&amp;</span><span class="self">self</span>.state);

                         coop.made_progress();
                         <span class="comment">// SAFETY: If `state.is_complete()` returns true, then the
                         // `VALUE_SENT` bit has been set and the sender side of the
                         // channel will no longer attempt to access the inner
                         // `UnsafeCell`. Therefore, it is now safe for us to access the
                         // cell.
                         </span><span class="kw">return match unsafe </span>{ <span class="self">self</span>.consume_value() } {
                             <span class="prelude-val">Some</span>(value) =&gt; Ready(<span class="prelude-val">Ok</span>(value)),
                             <span class="prelude-val">None </span>=&gt; Ready(<span class="prelude-val">Err</span>(RecvError(()))),
                         };
                     } <span class="kw">else </span>{
                         <span class="kw">unsafe </span>{ <span class="self">self</span>.rx_task.drop_task() };
                     }
                 }
             }

             <span class="kw">if </span>!state.is_rx_task_set() {
                 <span class="comment">// Attempt to set the task
                 </span><span class="kw">unsafe </span>{
                     <span class="self">self</span>.rx_task.set_task(cx);
                 }

                 <span class="comment">// Update the state
                 </span>state = State::set_rx_task(<span class="kw-2">&amp;</span><span class="self">self</span>.state);

                 <span class="kw">if </span>state.is_complete() {
                     coop.made_progress();
                     <span class="kw">match unsafe </span>{ <span class="self">self</span>.consume_value() } {
                         <span class="prelude-val">Some</span>(value) =&gt; Ready(<span class="prelude-val">Ok</span>(value)),
                         <span class="prelude-val">None </span>=&gt; Ready(<span class="prelude-val">Err</span>(RecvError(()))),
                     }
                 } <span class="kw">else </span>{
                     Pending
                 }
             } <span class="kw">else </span>{
                 Pending
             }
         }
     }

     <span class="doccomment">/// Called by `Receiver` to indicate that the value will never be received.
     </span><span class="kw">fn </span>close(<span class="kw-2">&amp;</span><span class="self">self</span>) {
         <span class="kw">let </span>prev = State::set_closed(<span class="kw-2">&amp;</span><span class="self">self</span>.state);

         <span class="kw">if </span>prev.is_tx_task_set() &amp;&amp; !prev.is_complete() {
             <span class="kw">unsafe </span>{
                 <span class="self">self</span>.tx_task.with_task(Waker::wake_by_ref);
             }
         }
     }

     <span class="doccomment">/// Consumes the value. This function does not check `state`.
     ///
     /// # Safety
     ///
     /// Calling this method concurrently on multiple threads will result in a
     /// data race. The `VALUE_SENT` state bit is used to ensure that only the
     /// sender *or* the receiver will call this method at a given point in time.
     /// If `VALUE_SENT` is not set, then only the sender may call this method;
     /// if it is set, then only the receiver may call this method.
     </span><span class="kw">unsafe fn </span>consume_value(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;T&gt; {
         <span class="self">self</span>.value.with_mut(|ptr| (<span class="kw-2">*</span>ptr).take())
     }
 }

 <span class="kw">unsafe impl</span>&lt;T: Send&gt; Send <span class="kw">for </span>Inner&lt;T&gt; {}
 <span class="kw">unsafe impl</span>&lt;T: Send&gt; Sync <span class="kw">for </span>Inner&lt;T&gt; {}

 <span class="kw">fn </span>mut_load(this: <span class="kw-2">&amp;mut </span>AtomicUsize) -&gt; usize {
     this.with_mut(|v| <span class="kw-2">*</span>v)
 }

 <span class="kw">impl</span>&lt;T&gt; Drop <span class="kw">for </span>Inner&lt;T&gt; {
     <span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
         <span class="kw">let </span>state = State(mut_load(<span class="kw-2">&amp;mut </span><span class="self">self</span>.state));

         <span class="kw">if </span>state.is_rx_task_set() {
             <span class="kw">unsafe </span>{
                 <span class="self">self</span>.rx_task.drop_task();
             }
         }

         <span class="kw">if </span>state.is_tx_task_set() {
             <span class="kw">unsafe </span>{
                 <span class="self">self</span>.tx_task.drop_task();
             }
         }
     }
 }

 <span class="kw">impl</span>&lt;T: fmt::Debug&gt; fmt::Debug <span class="kw">for </span>Inner&lt;T&gt; {
     <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, fmt: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
         <span class="kw">use </span>std::sync::atomic::Ordering::Relaxed;

         fmt.debug_struct(<span class="string">&quot;Inner&quot;</span>)
             .field(<span class="string">&quot;state&quot;</span>, <span class="kw-2">&amp;</span>State::load(<span class="kw-2">&amp;</span><span class="self">self</span>.state, Relaxed))
             .finish()
     }
 }

 <span class="doccomment">/// Indicates that a waker for the receiving task has been set.
 ///
 /// # Safety
 ///
 /// If this bit is not set, the `rx_task` field may be uninitialized.
 </span><span class="kw">const </span>RX_TASK_SET: usize = <span class="number">0b00001</span>;
 <span class="doccomment">/// Indicates that a value has been stored in the channel&#39;s inner `UnsafeCell`.
 ///
 /// # Safety
 ///
 /// This bit controls which side of the channel is permitted to access the
 /// `UnsafeCell`. If it is set, the `UnsafeCell` may ONLY be accessed by the
 /// receiver. If this bit is NOT set, the `UnsafeCell` may ONLY be accessed by
 /// the sender.
 </span><span class="kw">const </span>VALUE_SENT: usize = <span class="number">0b00010</span>;
 <span class="kw">const </span>CLOSED: usize = <span class="number">0b00100</span>;

 <span class="doccomment">/// Indicates that a waker for the sending task has been set.
 ///
 /// # Safety
 ///
 /// If this bit is not set, the `tx_task` field may be uninitialized.
 </span><span class="kw">const </span>TX_TASK_SET: usize = <span class="number">0b01000</span>;

 <span class="kw">impl </span>State {
     <span class="kw">fn </span>new() -&gt; State {
         State(<span class="number">0</span>)
     }

     <span class="kw">fn </span>is_complete(<span class="self">self</span>) -&gt; bool {
         <span class="self">self</span>.<span class="number">0 </span>&amp; VALUE_SENT == VALUE_SENT
     }

     <span class="kw">fn </span>set_complete(cell: <span class="kw-2">&amp;</span>AtomicUsize) -&gt; State {
         <span class="comment">// This method is a compare-and-swap loop rather than a fetch-or like
         // other `set_$WHATEVER` methods on `State`. This is because we must
         // check if the state has been closed before setting the `VALUE_SENT`
         // bit.
         //
         // We don&#39;t want to set both the `VALUE_SENT` bit if the `CLOSED`
         // bit is already set, because `VALUE_SENT` will tell the receiver that
         // it&#39;s okay to access the inner `UnsafeCell`. Immediately after calling
         // `set_complete`, if the channel was closed, the sender will _also_
         // access the `UnsafeCell` to take the value back out, so if a
         // `poll_recv` or `try_recv` call is occurring concurrently, both
         // threads may try to access the `UnsafeCell` if we were to set the
         // `VALUE_SENT` bit on a closed channel.
         </span><span class="kw">let </span><span class="kw-2">mut </span>state = cell.load(Ordering::Relaxed);
         <span class="kw">loop </span>{
             <span class="kw">if </span>State(state).is_closed() {
                 <span class="kw">break</span>;
             }
             <span class="comment">// TODO: This could be `Release`, followed by an `Acquire` fence *if*
             // the `RX_TASK_SET` flag is set. However, `loom` does not support
             // fences yet.
             </span><span class="kw">match </span>cell.compare_exchange_weak(
                 state,
                 state | VALUE_SENT,
                 Ordering::AcqRel,
                 Ordering::Acquire,
             ) {
                 <span class="prelude-val">Ok</span>(<span class="kw">_</span>) =&gt; <span class="kw">break</span>,
                 <span class="prelude-val">Err</span>(actual) =&gt; state = actual,
             }
         }
         State(state)
     }

     <span class="kw">fn </span>is_rx_task_set(<span class="self">self</span>) -&gt; bool {
         <span class="self">self</span>.<span class="number">0 </span>&amp; RX_TASK_SET == RX_TASK_SET
     }

     <span class="kw">fn </span>set_rx_task(cell: <span class="kw-2">&amp;</span>AtomicUsize) -&gt; State {
         <span class="kw">let </span>val = cell.fetch_or(RX_TASK_SET, AcqRel);
         State(val | RX_TASK_SET)
     }

     <span class="kw">fn </span>unset_rx_task(cell: <span class="kw-2">&amp;</span>AtomicUsize) -&gt; State {
         <span class="kw">let </span>val = cell.fetch_and(!RX_TASK_SET, AcqRel);
         State(val &amp; !RX_TASK_SET)
     }

     <span class="kw">fn </span>is_closed(<span class="self">self</span>) -&gt; bool {
         <span class="self">self</span>.<span class="number">0 </span>&amp; CLOSED == CLOSED
     }

     <span class="kw">fn </span>set_closed(cell: <span class="kw-2">&amp;</span>AtomicUsize) -&gt; State {
         <span class="comment">// Acquire because we want all later writes (attempting to poll) to be
         // ordered after this.
         </span><span class="kw">let </span>val = cell.fetch_or(CLOSED, Acquire);
         State(val)
     }

     <span class="kw">fn </span>set_tx_task(cell: <span class="kw-2">&amp;</span>AtomicUsize) -&gt; State {
         <span class="kw">let </span>val = cell.fetch_or(TX_TASK_SET, AcqRel);
         State(val | TX_TASK_SET)
     }

     <span class="kw">fn </span>unset_tx_task(cell: <span class="kw-2">&amp;</span>AtomicUsize) -&gt; State {
         <span class="kw">let </span>val = cell.fetch_and(!TX_TASK_SET, AcqRel);
         State(val &amp; !TX_TASK_SET)
     }

     <span class="kw">fn </span>is_tx_task_set(<span class="self">self</span>) -&gt; bool {
         <span class="self">self</span>.<span class="number">0 </span>&amp; TX_TASK_SET == TX_TASK_SET
     }

     <span class="kw">fn </span>as_usize(<span class="self">self</span>) -&gt; usize {
         <span class="self">self</span>.<span class="number">0
     </span>}

     <span class="kw">fn </span>load(cell: <span class="kw-2">&amp;</span>AtomicUsize, order: Ordering) -&gt; State {
         <span class="kw">let </span>val = cell.load(order);
         State(val)
     }
 }

 <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>State {
     <span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, fmt: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
         fmt.debug_struct(<span class="string">&quot;State&quot;</span>)
             .field(<span class="string">&quot;is_complete&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.is_complete())
             .field(<span class="string">&quot;is_closed&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.is_closed())
             .field(<span class="string">&quot;is_rx_task_set&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.is_rx_task_set())
             .field(<span class="string">&quot;is_tx_task_set&quot;</span>, <span class="kw-2">&amp;</span><span class="self">self</span>.is_tx_task_set())
             .finish()
     }
 }
 </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>