| <!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/watch.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>watch.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">"sync"</span>), allow(dead_code, unreachable_pub))] |
| |
| </span><span class="doccomment">//! A single-producer, multi-consumer channel that only retains the *last* sent |
| //! value. |
| //! |
| //! This channel is useful for watching for changes to a value from multiple |
| //! points in the code base, for example, changes to configuration values. |
| //! |
| //! # Usage |
| //! |
| //! [`channel`] returns a [`Sender`] / [`Receiver`] pair. These are the producer |
| //! and consumer halves of the channel. The channel is created with an initial |
| //! value. The **latest** value stored in the channel is accessed with |
| //! [`Receiver::borrow()`]. Awaiting [`Receiver::changed()`] waits for a new |
| //! value to be sent by the [`Sender`] half. |
| //! |
| //! # Examples |
| //! |
| //! ``` |
| //! use tokio::sync::watch; |
| //! |
| //! # async fn dox() -> Result<(), Box<dyn std::error::Error>> { |
| //! let (tx, mut rx) = watch::channel("hello"); |
| //! |
| //! tokio::spawn(async move { |
| //! while rx.changed().await.is_ok() { |
| //! println!("received = {:?}", *rx.borrow()); |
| //! } |
| //! }); |
| //! |
| //! tx.send("world")?; |
| //! # Ok(()) |
| //! # } |
| //! ``` |
| //! |
| //! # Closing |
| //! |
| //! [`Sender::is_closed`] and [`Sender::closed`] allow the producer to detect |
| //! when all [`Receiver`] handles have been dropped. This indicates that there |
| //! is no further interest in the values being produced and work can be stopped. |
| //! |
| //! The value in the channel will not be dropped until the sender and all receivers |
| //! have been dropped. |
| //! |
| //! # Thread safety |
| //! |
| //! Both [`Sender`] and [`Receiver`] are thread safe. They can be moved to other |
| //! threads and can be used in a concurrent environment. Clones of [`Receiver`] |
| //! handles may be moved to separate threads and also used concurrently. |
| //! |
| //! [`Sender`]: crate::sync::watch::Sender |
| //! [`Receiver`]: crate::sync::watch::Receiver |
| //! [`Receiver::changed()`]: crate::sync::watch::Receiver::changed |
| //! [`Receiver::borrow()`]: crate::sync::watch::Receiver::borrow |
| //! [`channel`]: crate::sync::watch::channel |
| //! [`Sender::is_closed`]: crate::sync::watch::Sender::is_closed |
| //! [`Sender::closed`]: crate::sync::watch::Sender::closed |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::sync::notify::Notify; |
| |
| <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::atomic::Ordering::Relaxed; |
| <span class="kw">use </span><span class="kw">crate</span>::loom::sync::{Arc, RwLock, RwLockReadGuard}; |
| <span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::mem; |
| <span class="kw">use </span>std::ops; |
| <span class="kw">use </span>std::panic; |
| |
| <span class="doccomment">/// Receives values from the associated [`Sender`](struct@Sender). |
| /// |
| /// Instances are created by the [`channel`](fn@channel) function. |
| /// |
| /// To turn this receiver into a `Stream`, you can use the [`WatchStream`] |
| /// wrapper. |
| /// |
| /// [`WatchStream`]: https://docs.rs/tokio-stream/0.1/tokio_stream/wrappers/struct.WatchStream.html |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>Receiver<T> { |
| <span class="doccomment">/// Pointer to the shared state |
| </span>shared: Arc<Shared<T>>, |
| |
| <span class="doccomment">/// Last observed version |
| </span>version: Version, |
| } |
| |
| <span class="doccomment">/// Sends values to the associated [`Receiver`](struct@Receiver). |
| /// |
| /// Instances are created by the [`channel`](fn@channel) function. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>Sender<T> { |
| shared: Arc<Shared<T>>, |
| } |
| |
| <span class="doccomment">/// Returns a reference to the inner value. |
| /// |
| /// Outstanding borrows hold a read lock on the inner value. This means that |
| /// long-lived borrows could cause the producer half to block. It is recommended |
| /// to keep the borrow as short-lived as possible. Additionally, if you are |
| /// running in an environment that allows `!Send` futures, you must ensure that |
| /// the returned `Ref` type is never held alive across an `.await` point, |
| /// otherwise, it can lead to a deadlock. |
| /// |
| /// The priority policy of the lock is dependent on the underlying lock |
| /// implementation, and this type does not guarantee that any particular policy |
| /// will be used. In particular, a producer which is waiting to acquire the lock |
| /// in `send` might or might not block concurrent calls to `borrow`, e.g.: |
| /// |
| /// <details><summary>Potential deadlock example</summary> |
| /// |
| /// ```text |
| /// // Task 1 (on thread A) | // Task 2 (on thread B) |
| /// let _ref1 = rx.borrow(); | |
| /// | // will block |
| /// | let _ = tx.send(()); |
| /// // may deadlock | |
| /// let _ref2 = rx.borrow(); | |
| /// ``` |
| /// </details> |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>Ref<<span class="lifetime">'a</span>, T> { |
| inner: RwLockReadGuard<<span class="lifetime">'a</span>, T>, |
| has_changed: bool, |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>, T> Ref<<span class="lifetime">'a</span>, T> { |
| <span class="doccomment">/// Indicates if the borrowed value is considered as _changed_ since the last |
| /// time it has been marked as seen. |
| /// |
| /// Unlike [`Receiver::has_changed()`], this method does not fail if the channel is closed. |
| /// |
| /// When borrowed from the [`Sender`] this function will always return `false`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, mut rx) = watch::channel("hello"); |
| /// |
| /// tx.send("goodbye").unwrap(); |
| /// // The sender does never consider the value as changed. |
| /// assert!(!tx.borrow().has_changed()); |
| /// |
| /// // Drop the sender immediately, just for testing purposes. |
| /// drop(tx); |
| /// |
| /// // Even if the sender has already been dropped... |
| /// assert!(rx.has_changed().is_err()); |
| /// // ...the modified value is still readable and detected as changed. |
| /// assert_eq!(*rx.borrow(), "goodbye"); |
| /// assert!(rx.borrow().has_changed()); |
| /// |
| /// // Read the changed value and mark it as seen. |
| /// { |
| /// let received = rx.borrow_and_update(); |
| /// assert_eq!(*received, "goodbye"); |
| /// assert!(received.has_changed()); |
| /// // Release the read lock when leaving this scope. |
| /// } |
| /// |
| /// // Now the value has already been marked as seen and could |
| /// // never be modified again (after the sender has been dropped). |
| /// assert!(!rx.borrow().has_changed()); |
| /// } |
| /// ``` |
| </span><span class="kw">pub fn </span>has_changed(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.has_changed |
| } |
| } |
| |
| <span class="kw">struct </span>Shared<T> { |
| <span class="doccomment">/// The most recent value. |
| </span>value: RwLock<T>, |
| |
| <span class="doccomment">/// The current version. |
| /// |
| /// The lowest bit represents a "closed" state. The rest of the bits |
| /// represent the current version. |
| </span>state: AtomicState, |
| |
| <span class="doccomment">/// Tracks the number of `Receiver` instances. |
| </span>ref_count_rx: AtomicUsize, |
| |
| <span class="doccomment">/// Notifies waiting receivers that the value changed. |
| </span>notify_rx: big_notify::BigNotify, |
| |
| <span class="doccomment">/// Notifies any task listening for `Receiver` dropped events. |
| </span>notify_tx: Notify, |
| } |
| |
| <span class="kw">impl</span><T: fmt::Debug> fmt::Debug <span class="kw">for </span>Shared<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 { |
| <span class="kw">let </span>state = <span class="self">self</span>.state.load(); |
| f.debug_struct(<span class="string">"Shared"</span>) |
| .field(<span class="string">"value"</span>, <span class="kw-2">&</span><span class="self">self</span>.value) |
| .field(<span class="string">"version"</span>, <span class="kw-2">&</span>state.version()) |
| .field(<span class="string">"is_closed"</span>, <span class="kw-2">&</span>state.is_closed()) |
| .field(<span class="string">"ref_count_rx"</span>, <span class="kw-2">&</span><span class="self">self</span>.ref_count_rx) |
| .finish() |
| } |
| } |
| |
| <span class="kw">pub mod </span>error { |
| <span class="doccomment">//! Watch error types. |
| |
| </span><span class="kw">use </span>std::fmt; |
| |
| <span class="doccomment">/// Error produced when sending a value fails. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>SendError<T>(<span class="kw">pub </span>T); |
| |
| <span class="comment">// ===== impl SendError ===== |
| |
| </span><span class="kw">impl</span><T: fmt::Debug> fmt::Display <span class="kw">for </span>SendError<T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, fmt: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| <span class="macro">write!</span>(fmt, <span class="string">"channel closed"</span>) |
| } |
| } |
| |
| <span class="kw">impl</span><T: fmt::Debug> std::error::Error <span class="kw">for </span>SendError<T> {} |
| |
| <span class="doccomment">/// Error produced when receiving a change notification. |
| </span><span class="attribute">#[derive(Debug, Clone)] |
| </span><span class="kw">pub struct </span>RecvError(<span class="kw">pub</span>(<span class="kw">super</span>) ()); |
| |
| <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">&</span><span class="self">self</span>, fmt: <span class="kw-2">&mut </span>fmt::Formatter<<span class="lifetime">'_</span>>) -> fmt::Result { |
| <span class="macro">write!</span>(fmt, <span class="string">"channel closed"</span>) |
| } |
| } |
| |
| <span class="kw">impl </span>std::error::Error <span class="kw">for </span>RecvError {} |
| } |
| |
| <span class="kw">mod </span>big_notify { |
| <span class="kw">use super</span>::<span class="kw-2">*</span>; |
| <span class="kw">use </span><span class="kw">crate</span>::sync::notify::Notified; |
| |
| <span class="comment">// To avoid contention on the lock inside the `Notify`, we store multiple |
| // copies of it. Then, we use either circular access or randomness to spread |
| // out threads over different `Notify` objects. |
| // |
| // Some simple benchmarks show that randomness performs slightly better than |
| // circular access (probably due to contention on `next`), so we prefer to |
| // use randomness when Tokio is compiled with a random number generator. |
| // |
| // When the random number generator is not available, we fall back to |
| // circular access. |
| |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>BigNotify { |
| <span class="attribute">#[cfg(not(all(not(loom), feature = <span class="string">"sync"</span>, any(feature = <span class="string">"rt"</span>, feature = <span class="string">"macros"</span>))))] |
| </span>next: AtomicUsize, |
| inner: [Notify; <span class="number">8</span>], |
| } |
| |
| <span class="kw">impl </span>BigNotify { |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| <span class="self">Self </span>{ |
| <span class="attribute">#[cfg(not(all( |
| not(loom), |
| feature = <span class="string">"sync"</span>, |
| any(feature = <span class="string">"rt"</span>, feature = <span class="string">"macros"</span>) |
| )))] |
| </span>next: AtomicUsize::new(<span class="number">0</span>), |
| inner: Default::default(), |
| } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>notify_waiters(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="kw">for </span>notify <span class="kw">in </span><span class="kw-2">&</span><span class="self">self</span>.inner { |
| notify.notify_waiters(); |
| } |
| } |
| |
| <span class="doccomment">/// This function implements the case where randomness is not available. |
| </span><span class="attribute">#[cfg(not(all(not(loom), feature = <span class="string">"sync"</span>, any(feature = <span class="string">"rt"</span>, feature = <span class="string">"macros"</span>))))] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>notified(<span class="kw-2">&</span><span class="self">self</span>) -> Notified<<span class="lifetime">'_</span>> { |
| <span class="kw">let </span>i = <span class="self">self</span>.next.fetch_add(<span class="number">1</span>, Relaxed) % <span class="number">8</span>; |
| <span class="self">self</span>.inner[i].notified() |
| } |
| |
| <span class="doccomment">/// This function implements the case where randomness is available. |
| </span><span class="attribute">#[cfg(all(not(loom), feature = <span class="string">"sync"</span>, any(feature = <span class="string">"rt"</span>, feature = <span class="string">"macros"</span>)))] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>notified(<span class="kw-2">&</span><span class="self">self</span>) -> Notified<<span class="lifetime">'_</span>> { |
| <span class="kw">let </span>i = <span class="kw">crate</span>::runtime::context::thread_rng_n(<span class="number">8</span>) <span class="kw">as </span>usize; |
| <span class="self">self</span>.inner[i].notified() |
| } |
| } |
| } |
| |
| <span class="kw">use </span><span class="self">self</span>::state::{AtomicState, Version}; |
| <span class="kw">mod </span>state { |
| <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::atomic::Ordering::SeqCst; |
| |
| <span class="kw">const </span>CLOSED: usize = <span class="number">1</span>; |
| |
| <span class="doccomment">/// The version part of the state. The lowest bit is always zero. |
| </span><span class="attribute">#[derive(Copy, Clone, Debug, Eq, PartialEq)] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Version(usize); |
| |
| <span class="doccomment">/// Snapshot of the state. The first bit is used as the CLOSED bit. |
| /// The remaining bits are used as the version. |
| /// |
| /// The CLOSED bit tracks whether the Sender has been dropped. Dropping all |
| /// receivers does not set it. |
| </span><span class="attribute">#[derive(Copy, Clone, Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>StateSnapshot(usize); |
| |
| <span class="doccomment">/// The state stored in an atomic integer. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>AtomicState(AtomicUsize); |
| |
| <span class="kw">impl </span>Version { |
| <span class="doccomment">/// Get the initial version when creating the channel. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>initial() -> <span class="self">Self </span>{ |
| Version(<span class="number">0</span>) |
| } |
| } |
| |
| <span class="kw">impl </span>StateSnapshot { |
| <span class="doccomment">/// Extract the version from the state. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>version(<span class="self">self</span>) -> Version { |
| Version(<span class="self">self</span>.<span class="number">0 </span>& !CLOSED) |
| } |
| |
| <span class="doccomment">/// Is the closed bit set? |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>is_closed(<span class="self">self</span>) -> bool { |
| (<span class="self">self</span>.<span class="number">0 </span>& CLOSED) == CLOSED |
| } |
| } |
| |
| <span class="kw">impl </span>AtomicState { |
| <span class="doccomment">/// Create a new `AtomicState` that is not closed and which has the |
| /// version set to `Version::initial()`. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| AtomicState(AtomicUsize::new(<span class="number">0</span>)) |
| } |
| |
| <span class="doccomment">/// Load the current value of the state. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>load(<span class="kw-2">&</span><span class="self">self</span>) -> StateSnapshot { |
| StateSnapshot(<span class="self">self</span>.<span class="number">0</span>.load(SeqCst)) |
| } |
| |
| <span class="doccomment">/// Increment the version counter. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>increment_version(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="comment">// Increment by two to avoid touching the CLOSED bit. |
| </span><span class="self">self</span>.<span class="number">0</span>.fetch_add(<span class="number">2</span>, SeqCst); |
| } |
| |
| <span class="doccomment">/// Set the closed bit in the state. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>set_closed(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="self">self</span>.<span class="number">0</span>.fetch_or(CLOSED, SeqCst); |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Creates a new watch channel, returning the "send" and "receive" handles. |
| /// |
| /// All values sent by [`Sender`] will become visible to the [`Receiver`] handles. |
| /// Only the last value sent is made available to the [`Receiver`] half. All |
| /// intermediate values are dropped. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// # async fn dox() -> Result<(), Box<dyn std::error::Error>> { |
| /// let (tx, mut rx) = watch::channel("hello"); |
| /// |
| /// tokio::spawn(async move { |
| /// while rx.changed().await.is_ok() { |
| /// println!("received = {:?}", *rx.borrow()); |
| /// } |
| /// }); |
| /// |
| /// tx.send("world")?; |
| /// # Ok(()) |
| /// # } |
| /// ``` |
| /// |
| /// [`Sender`]: struct@Sender |
| /// [`Receiver`]: struct@Receiver |
| </span><span class="kw">pub fn </span>channel<T>(init: T) -> (Sender<T>, Receiver<T>) { |
| <span class="kw">let </span>shared = Arc::new(Shared { |
| value: RwLock::new(init), |
| state: AtomicState::new(), |
| ref_count_rx: AtomicUsize::new(<span class="number">1</span>), |
| notify_rx: big_notify::BigNotify::new(), |
| notify_tx: Notify::new(), |
| }); |
| |
| <span class="kw">let </span>tx = Sender { |
| shared: shared.clone(), |
| }; |
| |
| <span class="kw">let </span>rx = Receiver { |
| shared, |
| version: Version::initial(), |
| }; |
| |
| (tx, rx) |
| } |
| |
| <span class="kw">impl</span><T> Receiver<T> { |
| <span class="kw">fn </span>from_shared(version: Version, shared: Arc<Shared<T>>) -> <span class="self">Self </span>{ |
| <span class="comment">// No synchronization necessary as this is only used as a counter and |
| // not memory access. |
| </span>shared.ref_count_rx.fetch_add(<span class="number">1</span>, Relaxed); |
| |
| <span class="self">Self </span>{ shared, version } |
| } |
| |
| <span class="doccomment">/// Returns a reference to the most recently sent value. |
| /// |
| /// This method does not mark the returned value as seen, so future calls to |
| /// [`changed`] may return immediately even if you have already seen the |
| /// value with a call to `borrow`. |
| /// |
| /// Outstanding borrows hold a read lock on the inner value. This means that |
| /// long-lived borrows could cause the producer half to block. It is recommended |
| /// to keep the borrow as short-lived as possible. Additionally, if you are |
| /// running in an environment that allows `!Send` futures, you must ensure that |
| /// the returned `Ref` type is never held alive across an `.await` point, |
| /// otherwise, it can lead to a deadlock. |
| /// |
| /// The priority policy of the lock is dependent on the underlying lock |
| /// implementation, and this type does not guarantee that any particular policy |
| /// will be used. In particular, a producer which is waiting to acquire the lock |
| /// in `send` might or might not block concurrent calls to `borrow`, e.g.: |
| /// |
| /// <details><summary>Potential deadlock example</summary> |
| /// |
| /// ```text |
| /// // Task 1 (on thread A) | // Task 2 (on thread B) |
| /// let _ref1 = rx.borrow(); | |
| /// | // will block |
| /// | let _ = tx.send(()); |
| /// // may deadlock | |
| /// let _ref2 = rx.borrow(); | |
| /// ``` |
| /// </details> |
| /// |
| /// [`changed`]: Receiver::changed |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// let (_, rx) = watch::channel("hello"); |
| /// assert_eq!(*rx.borrow(), "hello"); |
| /// ``` |
| </span><span class="kw">pub fn </span>borrow(<span class="kw-2">&</span><span class="self">self</span>) -> Ref<<span class="lifetime">'_</span>, T> { |
| <span class="kw">let </span>inner = <span class="self">self</span>.shared.value.read().unwrap(); |
| |
| <span class="comment">// After obtaining a read-lock no concurrent writes could occur |
| // and the loaded version matches that of the borrowed reference. |
| </span><span class="kw">let </span>new_version = <span class="self">self</span>.shared.state.load().version(); |
| <span class="kw">let </span>has_changed = <span class="self">self</span>.version != new_version; |
| |
| Ref { inner, has_changed } |
| } |
| |
| <span class="doccomment">/// Returns a reference to the most recently sent value and marks that value |
| /// as seen. |
| /// |
| /// This method marks the current value as seen. Subsequent calls to [`changed`] |
| /// will not return immediately until the [`Sender`] has modified the shared |
| /// value again. |
| /// |
| /// Outstanding borrows hold a read lock on the inner value. This means that |
| /// long-lived borrows could cause the producer half to block. It is recommended |
| /// to keep the borrow as short-lived as possible. Additionally, if you are |
| /// running in an environment that allows `!Send` futures, you must ensure that |
| /// the returned `Ref` type is never held alive across an `.await` point, |
| /// otherwise, it can lead to a deadlock. |
| /// |
| /// The priority policy of the lock is dependent on the underlying lock |
| /// implementation, and this type does not guarantee that any particular policy |
| /// will be used. In particular, a producer which is waiting to acquire the lock |
| /// in `send` might or might not block concurrent calls to `borrow`, e.g.: |
| /// |
| /// <details><summary>Potential deadlock example</summary> |
| /// |
| /// ```text |
| /// // Task 1 (on thread A) | // Task 2 (on thread B) |
| /// let _ref1 = rx1.borrow_and_update(); | |
| /// | // will block |
| /// | let _ = tx.send(()); |
| /// // may deadlock | |
| /// let _ref2 = rx2.borrow_and_update(); | |
| /// ``` |
| /// </details> |
| /// |
| /// [`changed`]: Receiver::changed |
| </span><span class="kw">pub fn </span>borrow_and_update(<span class="kw-2">&mut </span><span class="self">self</span>) -> Ref<<span class="lifetime">'_</span>, T> { |
| <span class="kw">let </span>inner = <span class="self">self</span>.shared.value.read().unwrap(); |
| |
| <span class="comment">// After obtaining a read-lock no concurrent writes could occur |
| // and the loaded version matches that of the borrowed reference. |
| </span><span class="kw">let </span>new_version = <span class="self">self</span>.shared.state.load().version(); |
| <span class="kw">let </span>has_changed = <span class="self">self</span>.version != new_version; |
| |
| <span class="comment">// Mark the shared value as seen by updating the version |
| </span><span class="self">self</span>.version = new_version; |
| |
| Ref { inner, has_changed } |
| } |
| |
| <span class="doccomment">/// Checks if this channel contains a message that this receiver has not yet |
| /// seen. The new value is not marked as seen. |
| /// |
| /// Although this method is called `has_changed`, it does not check new |
| /// messages for equality, so this call will return true even if the new |
| /// message is equal to the old message. |
| /// |
| /// Returns an error if the channel has been closed. |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, mut rx) = watch::channel("hello"); |
| /// |
| /// tx.send("goodbye").unwrap(); |
| /// |
| /// assert!(rx.has_changed().unwrap()); |
| /// assert_eq!(*rx.borrow_and_update(), "goodbye"); |
| /// |
| /// // The value has been marked as seen |
| /// assert!(!rx.has_changed().unwrap()); |
| /// |
| /// drop(tx); |
| /// // The `tx` handle has been dropped |
| /// assert!(rx.has_changed().is_err()); |
| /// } |
| /// ``` |
| </span><span class="kw">pub fn </span>has_changed(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><bool, error::RecvError> { |
| <span class="comment">// Load the version from the state |
| </span><span class="kw">let </span>state = <span class="self">self</span>.shared.state.load(); |
| <span class="kw">if </span>state.is_closed() { |
| <span class="comment">// The sender has dropped. |
| </span><span class="kw">return </span><span class="prelude-val">Err</span>(error::RecvError(())); |
| } |
| <span class="kw">let </span>new_version = state.version(); |
| |
| <span class="prelude-val">Ok</span>(<span class="self">self</span>.version != new_version) |
| } |
| |
| <span class="doccomment">/// Waits for a change notification, then marks the newest value as seen. |
| /// |
| /// If the newest value in the channel has not yet been marked seen when |
| /// this method is called, the method marks that value seen and returns |
| /// immediately. If the newest value has already been marked seen, then the |
| /// method sleeps until a new message is sent by the [`Sender`] connected to |
| /// this `Receiver`, or until the [`Sender`] is dropped. |
| /// |
| /// This method returns an error if and only if the [`Sender`] is dropped. |
| /// |
| /// # Cancel safety |
| /// |
| /// This method is cancel safe. If you use it as the event in a |
| /// [`tokio::select!`](crate::select) statement and some other branch |
| /// completes first, then it is guaranteed that no values have been marked |
| /// seen by this call to `changed`. |
| /// |
| /// [`Sender`]: struct@Sender |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, mut rx) = watch::channel("hello"); |
| /// |
| /// tokio::spawn(async move { |
| /// tx.send("goodbye").unwrap(); |
| /// }); |
| /// |
| /// assert!(rx.changed().await.is_ok()); |
| /// assert_eq!(*rx.borrow(), "goodbye"); |
| /// |
| /// // The `tx` handle has been dropped |
| /// assert!(rx.changed().await.is_err()); |
| /// } |
| /// ``` |
| </span><span class="kw">pub async fn </span>changed(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><(), error::RecvError> { |
| changed_impl(<span class="kw-2">&</span><span class="self">self</span>.shared, <span class="kw-2">&mut </span><span class="self">self</span>.version).<span class="kw">await |
| </span>} |
| |
| <span class="doccomment">/// Waits for a value that satisifes the provided condition. |
| /// |
| /// This method will call the provided closure whenever something is sent on |
| /// the channel. Once the closure returns `true`, this method will return a |
| /// reference to the value that was passed to the closure. |
| /// |
| /// Before `wait_for` starts waiting for changes, it will call the closure |
| /// on the current value. If the closure returns `true` when given the |
| /// current value, then `wait_for` will immediately return a reference to |
| /// the current value. This is the case even if the current value is already |
| /// considered seen. |
| /// |
| /// The watch channel only keeps track of the most recent value, so if |
| /// several messages are sent faster than `wait_for` is able to call the |
| /// closure, then it may skip some updates. Whenever the closure is called, |
| /// it will be called with the most recent value. |
| /// |
| /// When this function returns, the value that was passed to the closure |
| /// when it returned `true` will be considered seen. |
| /// |
| /// If the channel is closed, then `wait_for` will return a `RecvError`. |
| /// Once this happens, no more messages can ever be sent on the channel. |
| /// When an error is returned, it is guaranteed that the closure has been |
| /// called on the last value, and that it returned `false` for that value. |
| /// (If the closure returned `true`, then the last value would have been |
| /// returned instead of the error.) |
| /// |
| /// Like the `borrow` method, the returned borrow holds a read lock on the |
| /// inner value. This means that long-lived borrows could cause the producer |
| /// half to block. It is recommended to keep the borrow as short-lived as |
| /// possible. See the documentation of `borrow` for more information on |
| /// this. |
| /// |
| /// [`Receiver::changed()`]: crate::sync::watch::Receiver::changed |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// |
| /// async fn main() { |
| /// let (tx, _rx) = watch::channel("hello"); |
| /// |
| /// tx.send("goodbye").unwrap(); |
| /// |
| /// // here we subscribe to a second receiver |
| /// // now in case of using `changed` we would have |
| /// // to first check the current value and then wait |
| /// // for changes or else `changed` would hang. |
| /// let mut rx2 = tx.subscribe(); |
| /// |
| /// // in place of changed we have use `wait_for` |
| /// // which would automatically check the current value |
| /// // and wait for changes until the closure returns true. |
| /// assert!(rx2.wait_for(|val| *val == "goodbye").await.is_ok()); |
| /// assert_eq!(*rx2.borrow(), "goodbye"); |
| /// } |
| /// ``` |
| </span><span class="kw">pub async fn </span>wait_for( |
| <span class="kw-2">&mut </span><span class="self">self</span>, |
| <span class="kw-2">mut </span>f: <span class="kw">impl </span>FnMut(<span class="kw-2">&</span>T) -> bool, |
| ) -> <span class="prelude-ty">Result</span><Ref<<span class="lifetime">'_</span>, T>, error::RecvError> { |
| <span class="kw">let </span><span class="kw-2">mut </span>closed = <span class="bool-val">false</span>; |
| <span class="kw">loop </span>{ |
| { |
| <span class="kw">let </span>inner = <span class="self">self</span>.shared.value.read().unwrap(); |
| |
| <span class="kw">let </span>new_version = <span class="self">self</span>.shared.state.load().version(); |
| <span class="kw">let </span>has_changed = <span class="self">self</span>.version != new_version; |
| <span class="self">self</span>.version = new_version; |
| |
| <span class="kw">if </span>(!closed || has_changed) && f(<span class="kw-2">&</span>inner) { |
| <span class="kw">return </span><span class="prelude-val">Ok</span>(Ref { inner, has_changed }); |
| } |
| } |
| |
| <span class="kw">if </span>closed { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(error::RecvError(())); |
| } |
| |
| <span class="comment">// Wait for the value to change. |
| </span>closed = changed_impl(<span class="kw-2">&</span><span class="self">self</span>.shared, <span class="kw-2">&mut </span><span class="self">self</span>.version).<span class="kw">await</span>.is_err(); |
| } |
| } |
| |
| <span class="doccomment">/// Returns `true` if receivers belong to the same channel. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let (tx, rx) = tokio::sync::watch::channel(true); |
| /// let rx2 = rx.clone(); |
| /// assert!(rx.same_channel(&rx2)); |
| /// |
| /// let (tx3, rx3) = tokio::sync::watch::channel(true); |
| /// assert!(!rx3.same_channel(&rx2)); |
| /// ``` |
| </span><span class="kw">pub fn </span>same_channel(<span class="kw-2">&</span><span class="self">self</span>, other: <span class="kw-2">&</span><span class="self">Self</span>) -> bool { |
| Arc::ptr_eq(<span class="kw-2">&</span><span class="self">self</span>.shared, <span class="kw-2">&</span>other.shared) |
| } |
| |
| <span class="macro">cfg_process_driver! </span>{ |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>try_has_changed(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="prelude-ty">Result</span><(), error::RecvError>> { |
| maybe_changed(<span class="kw-2">&</span><span class="self">self</span>.shared, <span class="kw-2">&mut </span><span class="self">self</span>.version) |
| } |
| } |
| } |
| |
| <span class="kw">fn </span>maybe_changed<T>( |
| shared: <span class="kw-2">&</span>Shared<T>, |
| version: <span class="kw-2">&mut </span>Version, |
| ) -> <span class="prelude-ty">Option</span><<span class="prelude-ty">Result</span><(), error::RecvError>> { |
| <span class="comment">// Load the version from the state |
| </span><span class="kw">let </span>state = shared.state.load(); |
| <span class="kw">let </span>new_version = state.version(); |
| |
| <span class="kw">if </span><span class="kw-2">*</span>version != new_version { |
| <span class="comment">// Observe the new version and return |
| </span><span class="kw-2">*</span>version = new_version; |
| <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="prelude-val">Ok</span>(())); |
| } |
| |
| <span class="kw">if </span>state.is_closed() { |
| <span class="comment">// All receivers have dropped. |
| </span><span class="kw">return </span><span class="prelude-val">Some</span>(<span class="prelude-val">Err</span>(error::RecvError(()))); |
| } |
| |
| <span class="prelude-val">None |
| </span>} |
| |
| <span class="kw">async fn </span>changed_impl<T>( |
| shared: <span class="kw-2">&</span>Shared<T>, |
| version: <span class="kw-2">&mut </span>Version, |
| ) -> <span class="prelude-ty">Result</span><(), error::RecvError> { |
| <span class="kw">loop </span>{ |
| <span class="comment">// In order to avoid a race condition, we first request a notification, |
| // **then** check the current value's version. If a new version exists, |
| // the notification request is dropped. |
| </span><span class="kw">let </span>notified = shared.notify_rx.notified(); |
| |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(ret) = maybe_changed(shared, version) { |
| <span class="kw">return </span>ret; |
| } |
| |
| notified.<span class="kw">await</span>; |
| <span class="comment">// loop around again in case the wake-up was spurious |
| </span>} |
| } |
| |
| <span class="kw">impl</span><T> Clone <span class="kw">for </span>Receiver<T> { |
| <span class="kw">fn </span>clone(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="self">Self </span>{ |
| <span class="kw">let </span>version = <span class="self">self</span>.version; |
| <span class="kw">let </span>shared = <span class="self">self</span>.shared.clone(); |
| |
| <span class="self">Self</span>::from_shared(version, shared) |
| } |
| } |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>Receiver<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="comment">// No synchronization necessary as this is only used as a counter and |
| // not memory access. |
| </span><span class="kw">if </span><span class="number">1 </span>== <span class="self">self</span>.shared.ref_count_rx.fetch_sub(<span class="number">1</span>, Relaxed) { |
| <span class="comment">// This is the last `Receiver` handle, tasks waiting on `Sender::closed()` |
| </span><span class="self">self</span>.shared.notify_tx.notify_waiters(); |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T> Sender<T> { |
| <span class="doccomment">/// Sends a new value via the channel, notifying all receivers. |
| /// |
| /// This method fails if the channel is closed, which is the case when |
| /// every receiver has been dropped. It is possible to reopen the channel |
| /// using the [`subscribe`] method. However, when `send` fails, the value |
| /// isn't made available for future receivers (but returned with the |
| /// [`SendError`]). |
| /// |
| /// To always make a new value available for future receivers, even if no |
| /// receiver currently exists, one of the other send methods |
| /// ([`send_if_modified`], [`send_modify`], or [`send_replace`]) can be |
| /// used instead. |
| /// |
| /// [`subscribe`]: Sender::subscribe |
| /// [`SendError`]: error::SendError |
| /// [`send_if_modified`]: Sender::send_if_modified |
| /// [`send_modify`]: Sender::send_modify |
| /// [`send_replace`]: Sender::send_replace |
| </span><span class="kw">pub fn </span>send(<span class="kw-2">&</span><span class="self">self</span>, value: T) -> <span class="prelude-ty">Result</span><(), error::SendError<T>> { |
| <span class="comment">// This is pretty much only useful as a hint anyway, so synchronization isn't critical. |
| </span><span class="kw">if </span><span class="number">0 </span>== <span class="self">self</span>.receiver_count() { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(error::SendError(value)); |
| } |
| |
| <span class="self">self</span>.send_replace(value); |
| <span class="prelude-val">Ok</span>(()) |
| } |
| |
| <span class="doccomment">/// Modifies the watched value **unconditionally** in-place, |
| /// notifying all receivers. |
| /// |
| /// This can be useful for modifying the watched value, without |
| /// having to allocate a new instance. Additionally, this |
| /// method permits sending values even when there are no receivers. |
| /// |
| /// Prefer to use the more versatile function [`Self::send_if_modified()`] |
| /// if the value is only modified conditionally during the mutable borrow |
| /// to prevent unneeded change notifications for unmodified values. |
| /// |
| /// # Panics |
| /// |
| /// This function panics when the invocation of the `modify` closure panics. |
| /// No receivers are notified when panicking. All changes of the watched |
| /// value applied by the closure before panicking will be visible in |
| /// subsequent calls to `borrow`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// struct State { |
| /// counter: usize, |
| /// } |
| /// let (state_tx, state_rx) = watch::channel(State { counter: 0 }); |
| /// state_tx.send_modify(|state| state.counter += 1); |
| /// assert_eq!(state_rx.borrow().counter, 1); |
| /// ``` |
| </span><span class="kw">pub fn </span>send_modify<F>(<span class="kw-2">&</span><span class="self">self</span>, modify: F) |
| <span class="kw">where |
| </span>F: FnOnce(<span class="kw-2">&mut </span>T), |
| { |
| <span class="self">self</span>.send_if_modified(|value| { |
| modify(value); |
| <span class="bool-val">true |
| </span>}); |
| } |
| |
| <span class="doccomment">/// Modifies the watched value **conditionally** in-place, |
| /// notifying all receivers only if modified. |
| /// |
| /// This can be useful for modifying the watched value, without |
| /// having to allocate a new instance. Additionally, this |
| /// method permits sending values even when there are no receivers. |
| /// |
| /// The `modify` closure must return `true` if the value has actually |
| /// been modified during the mutable borrow. It should only return `false` |
| /// if the value is guaranteed to be unmodified despite the mutable |
| /// borrow. |
| /// |
| /// Receivers are only notified if the closure returned `true`. If the |
| /// closure has modified the value but returned `false` this results |
| /// in a *silent modification*, i.e. the modified value will be visible |
| /// in subsequent calls to `borrow`, but receivers will not receive |
| /// a change notification. |
| /// |
| /// Returns the result of the closure, i.e. `true` if the value has |
| /// been modified and `false` otherwise. |
| /// |
| /// # Panics |
| /// |
| /// This function panics when the invocation of the `modify` closure panics. |
| /// No receivers are notified when panicking. All changes of the watched |
| /// value applied by the closure before panicking will be visible in |
| /// subsequent calls to `borrow`. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// struct State { |
| /// counter: usize, |
| /// } |
| /// let (state_tx, mut state_rx) = watch::channel(State { counter: 1 }); |
| /// let inc_counter_if_odd = |state: &mut State| { |
| /// if state.counter % 2 == 1 { |
| /// state.counter += 1; |
| /// return true; |
| /// } |
| /// false |
| /// }; |
| /// |
| /// assert_eq!(state_rx.borrow().counter, 1); |
| /// |
| /// assert!(!state_rx.has_changed().unwrap()); |
| /// assert!(state_tx.send_if_modified(inc_counter_if_odd)); |
| /// assert!(state_rx.has_changed().unwrap()); |
| /// assert_eq!(state_rx.borrow_and_update().counter, 2); |
| /// |
| /// assert!(!state_rx.has_changed().unwrap()); |
| /// assert!(!state_tx.send_if_modified(inc_counter_if_odd)); |
| /// assert!(!state_rx.has_changed().unwrap()); |
| /// assert_eq!(state_rx.borrow_and_update().counter, 2); |
| /// ``` |
| </span><span class="kw">pub fn </span>send_if_modified<F>(<span class="kw-2">&</span><span class="self">self</span>, modify: F) -> bool |
| <span class="kw">where |
| </span>F: FnOnce(<span class="kw-2">&mut </span>T) -> bool, |
| { |
| { |
| <span class="comment">// Acquire the write lock and update the value. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>lock = <span class="self">self</span>.shared.value.write().unwrap(); |
| |
| <span class="comment">// Update the value and catch possible panic inside func. |
| </span><span class="kw">let </span>result = panic::catch_unwind(panic::AssertUnwindSafe(|| modify(<span class="kw-2">&mut </span>lock))); |
| <span class="kw">match </span>result { |
| <span class="prelude-val">Ok</span>(modified) => { |
| <span class="kw">if </span>!modified { |
| <span class="comment">// Abort, i.e. don't notify receivers if unmodified |
| </span><span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| <span class="comment">// Continue if modified |
| </span>} |
| <span class="prelude-val">Err</span>(panicked) => { |
| <span class="comment">// Drop the lock to avoid poisoning it. |
| </span>drop(lock); |
| <span class="comment">// Forward the panic to the caller. |
| </span>panic::resume_unwind(panicked); |
| <span class="comment">// Unreachable |
| </span>} |
| }; |
| |
| <span class="self">self</span>.shared.state.increment_version(); |
| |
| <span class="comment">// Release the write lock. |
| // |
| // Incrementing the version counter while holding the lock ensures |
| // that receivers are able to figure out the version number of the |
| // value they are currently looking at. |
| </span>drop(lock); |
| } |
| |
| <span class="self">self</span>.shared.notify_rx.notify_waiters(); |
| |
| <span class="bool-val">true |
| </span>} |
| |
| <span class="doccomment">/// Sends a new value via the channel, notifying all receivers and returning |
| /// the previous value in the channel. |
| /// |
| /// This can be useful for reusing the buffers inside a watched value. |
| /// Additionally, this method permits sending values even when there are no |
| /// receivers. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// let (tx, _rx) = watch::channel(1); |
| /// assert_eq!(tx.send_replace(2), 1); |
| /// assert_eq!(tx.send_replace(3), 2); |
| /// ``` |
| </span><span class="kw">pub fn </span>send_replace(<span class="kw-2">&</span><span class="self">self</span>, <span class="kw-2">mut </span>value: T) -> T { |
| <span class="comment">// swap old watched value with the new one |
| </span><span class="self">self</span>.send_modify(|old| mem::swap(old, <span class="kw-2">&mut </span>value)); |
| |
| value |
| } |
| |
| <span class="doccomment">/// Returns a reference to the most recently sent value |
| /// |
| /// Outstanding borrows hold a read lock on the inner value. This means that |
| /// long-lived borrows could cause the producer half to block. It is recommended |
| /// to keep the borrow as short-lived as possible. Additionally, if you are |
| /// running in an environment that allows `!Send` futures, you must ensure that |
| /// the returned `Ref` type is never held alive across an `.await` point, |
| /// otherwise, it can lead to a deadlock. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// let (tx, _) = watch::channel("hello"); |
| /// assert_eq!(*tx.borrow(), "hello"); |
| /// ``` |
| </span><span class="kw">pub fn </span>borrow(<span class="kw-2">&</span><span class="self">self</span>) -> Ref<<span class="lifetime">'_</span>, T> { |
| <span class="kw">let </span>inner = <span class="self">self</span>.shared.value.read().unwrap(); |
| |
| <span class="comment">// The sender/producer always sees the current version |
| </span><span class="kw">let </span>has_changed = <span class="bool-val">false</span>; |
| |
| Ref { inner, has_changed } |
| } |
| |
| <span class="doccomment">/// Checks if the channel has been closed. This happens when all receivers |
| /// have dropped. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// let (tx, rx) = tokio::sync::watch::channel(()); |
| /// assert!(!tx.is_closed()); |
| /// |
| /// drop(rx); |
| /// assert!(tx.is_closed()); |
| /// ``` |
| </span><span class="kw">pub fn </span>is_closed(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.receiver_count() == <span class="number">0 |
| </span>} |
| |
| <span class="doccomment">/// Completes when all receivers have dropped. |
| /// |
| /// This allows the producer to get notified when interest in the produced |
| /// values is canceled and immediately stop doing work. |
| /// |
| /// # Cancel safety |
| /// |
| /// This method is cancel safe. Once the channel is closed, it stays closed |
| /// forever and all future calls to `closed` will return immediately. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, rx) = watch::channel("hello"); |
| /// |
| /// tokio::spawn(async move { |
| /// // use `rx` |
| /// drop(rx); |
| /// }); |
| /// |
| /// // Waits for `rx` to drop |
| /// tx.closed().await; |
| /// println!("the `rx` handles dropped") |
| /// } |
| /// ``` |
| </span><span class="kw">pub async fn </span>closed(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="kw">while </span><span class="self">self</span>.receiver_count() > <span class="number">0 </span>{ |
| <span class="kw">let </span>notified = <span class="self">self</span>.shared.notify_tx.notified(); |
| |
| <span class="kw">if </span><span class="self">self</span>.receiver_count() == <span class="number">0 </span>{ |
| <span class="kw">return</span>; |
| } |
| |
| notified.<span class="kw">await</span>; |
| <span class="comment">// The channel could have been reopened in the meantime by calling |
| // `subscribe`, so we loop again. |
| </span>} |
| } |
| |
| <span class="doccomment">/// Creates a new [`Receiver`] connected to this `Sender`. |
| /// |
| /// All messages sent before this call to `subscribe` are initially marked |
| /// as seen by the new `Receiver`. |
| /// |
| /// This method can be called even if there are no other receivers. In this |
| /// case, the channel is reopened. |
| /// |
| /// # Examples |
| /// |
| /// The new channel will receive messages sent on this `Sender`. |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, _rx) = watch::channel(0u64); |
| /// |
| /// tx.send(5).unwrap(); |
| /// |
| /// let rx = tx.subscribe(); |
| /// assert_eq!(5, *rx.borrow()); |
| /// |
| /// tx.send(10).unwrap(); |
| /// assert_eq!(10, *rx.borrow()); |
| /// } |
| /// ``` |
| /// |
| /// The most recent message is considered seen by the channel, so this test |
| /// is guaranteed to pass. |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// use tokio::time::Duration; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, _rx) = watch::channel(0u64); |
| /// tx.send(5).unwrap(); |
| /// let mut rx = tx.subscribe(); |
| /// |
| /// tokio::spawn(async move { |
| /// // by spawning and sleeping, the message is sent after `main` |
| /// // hits the call to `changed`. |
| /// # if false { |
| /// tokio::time::sleep(Duration::from_millis(10)).await; |
| /// # } |
| /// tx.send(100).unwrap(); |
| /// }); |
| /// |
| /// rx.changed().await.unwrap(); |
| /// assert_eq!(100, *rx.borrow()); |
| /// } |
| /// ``` |
| </span><span class="kw">pub fn </span>subscribe(<span class="kw-2">&</span><span class="self">self</span>) -> Receiver<T> { |
| <span class="kw">let </span>shared = <span class="self">self</span>.shared.clone(); |
| <span class="kw">let </span>version = shared.state.load().version(); |
| |
| <span class="comment">// The CLOSED bit in the state tracks only whether the sender is |
| // dropped, so we do not need to unset it if this reopens the channel. |
| </span>Receiver::from_shared(version, shared) |
| } |
| |
| <span class="doccomment">/// Returns the number of receivers that currently exist. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::watch; |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let (tx, rx1) = watch::channel("hello"); |
| /// |
| /// assert_eq!(1, tx.receiver_count()); |
| /// |
| /// let mut _rx2 = rx1.clone(); |
| /// |
| /// assert_eq!(2, tx.receiver_count()); |
| /// } |
| /// ``` |
| </span><span class="kw">pub fn </span>receiver_count(<span class="kw-2">&</span><span class="self">self</span>) -> usize { |
| <span class="self">self</span>.shared.ref_count_rx.load(Relaxed) |
| } |
| } |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>Sender<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="self">self</span>.shared.state.set_closed(); |
| <span class="self">self</span>.shared.notify_rx.notify_waiters(); |
| } |
| } |
| |
| <span class="comment">// ===== impl Ref ===== |
| |
| </span><span class="kw">impl</span><T> ops::Deref <span class="kw">for </span>Ref<<span class="lifetime">'_</span>, T> { |
| <span class="kw">type </span>Target = T; |
| |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="self">self</span>.inner.deref() |
| } |
| } |
| |
| <span class="attribute">#[cfg(all(test, loom))] |
| </span><span class="kw">mod </span>tests { |
| <span class="kw">use </span>futures::future::FutureExt; |
| <span class="kw">use </span>loom::thread; |
| |
| <span class="comment">// test for https://github.com/tokio-rs/tokio/issues/3168 |
| </span><span class="attribute">#[test] |
| </span><span class="kw">fn </span>watch_spurious_wakeup() { |
| loom::model(|| { |
| <span class="kw">let </span>(send, <span class="kw-2">mut </span>recv) = <span class="kw">crate</span>::sync::watch::channel(<span class="number">0i32</span>); |
| |
| send.send(<span class="number">1</span>).unwrap(); |
| |
| <span class="kw">let </span>send_thread = thread::spawn(<span class="kw">move </span>|| { |
| send.send(<span class="number">2</span>).unwrap(); |
| send |
| }); |
| |
| recv.changed().now_or_never(); |
| |
| <span class="kw">let </span>send = send_thread.join().unwrap(); |
| <span class="kw">let </span>recv_thread = thread::spawn(<span class="kw">move </span>|| { |
| recv.changed().now_or_never(); |
| recv.changed().now_or_never(); |
| recv |
| }); |
| |
| send.send(<span class="number">3</span>).unwrap(); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>recv = recv_thread.join().unwrap(); |
| <span class="kw">let </span>send_thread = thread::spawn(<span class="kw">move </span>|| { |
| send.send(<span class="number">2</span>).unwrap(); |
| }); |
| |
| recv.changed().now_or_never(); |
| |
| send_thread.join().unwrap(); |
| }); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>watch_borrow() { |
| loom::model(|| { |
| <span class="kw">let </span>(send, <span class="kw-2">mut </span>recv) = <span class="kw">crate</span>::sync::watch::channel(<span class="number">0i32</span>); |
| |
| <span class="macro">assert!</span>(send.borrow().eq(<span class="kw-2">&</span><span class="number">0</span>)); |
| <span class="macro">assert!</span>(recv.borrow().eq(<span class="kw-2">&</span><span class="number">0</span>)); |
| |
| send.send(<span class="number">1</span>).unwrap(); |
| <span class="macro">assert!</span>(send.borrow().eq(<span class="kw-2">&</span><span class="number">1</span>)); |
| |
| <span class="kw">let </span>send_thread = thread::spawn(<span class="kw">move </span>|| { |
| send.send(<span class="number">2</span>).unwrap(); |
| send |
| }); |
| |
| recv.changed().now_or_never(); |
| |
| <span class="kw">let </span>send = send_thread.join().unwrap(); |
| <span class="kw">let </span>recv_thread = thread::spawn(<span class="kw">move </span>|| { |
| recv.changed().now_or_never(); |
| recv.changed().now_or_never(); |
| recv |
| }); |
| |
| send.send(<span class="number">3</span>).unwrap(); |
| |
| <span class="kw">let </span>recv = recv_thread.join().unwrap(); |
| <span class="macro">assert!</span>(recv.borrow().eq(<span class="kw-2">&</span><span class="number">3</span>)); |
| <span class="macro">assert!</span>(send.borrow().eq(<span class="kw-2">&</span><span class="number">3</span>)); |
| |
| send.send(<span class="number">2</span>).unwrap(); |
| |
| thread::spawn(<span class="kw">move </span>|| { |
| <span class="macro">assert!</span>(recv.borrow().eq(<span class="kw-2">&</span><span class="number">2</span>)); |
| }); |
| <span class="macro">assert!</span>(send.borrow().eq(<span class="kw-2">&</span><span class="number">2</span>)); |
| }); |
| } |
| } |
| </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> |