| <!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/once_cell.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>once_cell.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="kw">use super</span>::{Semaphore, SemaphorePermit, TryAcquireError}; |
| <span class="kw">use </span><span class="kw">crate</span>::loom::cell::UnsafeCell; |
| <span class="kw">use </span>std::error::Error; |
| <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::ops::Drop; |
| <span class="kw">use </span>std::ptr; |
| <span class="kw">use </span>std::sync::atomic::{AtomicBool, Ordering}; |
| |
| <span class="comment">// This file contains an implementation of an OnceCell. The principle |
| // behind the safety the of the cell is that any thread with an `&OnceCell` may |
| // access the `value` field according the following rules: |
| // |
| // 1. When `value_set` is false, the `value` field may be modified by the |
| // thread holding the permit on the semaphore. |
| // 2. When `value_set` is true, the `value` field may be accessed immutably by |
| // any thread. |
| // |
| // It is an invariant that if the semaphore is closed, then `value_set` is true. |
| // The reverse does not necessarily hold — but if not, the semaphore may not |
| // have any available permits. |
| // |
| // A thread with a `&mut OnceCell` may modify the value in any way it wants as |
| // long as the invariants are upheld. |
| |
| </span><span class="doccomment">/// A thread-safe cell that can be written to only once. |
| /// |
| /// A `OnceCell` is typically used for global variables that need to be |
| /// initialized once on first use, but need no further changes. The `OnceCell` |
| /// in Tokio allows the initialization procedure to be asynchronous. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use tokio::sync::OnceCell; |
| /// |
| /// async fn some_computation() -> u32 { |
| /// 1 + 1 |
| /// } |
| /// |
| /// static ONCE: OnceCell<u32> = OnceCell::const_new(); |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let result = ONCE.get_or_init(some_computation).await; |
| /// assert_eq!(*result, 2); |
| /// } |
| /// ``` |
| /// |
| /// It is often useful to write a wrapper method for accessing the value. |
| /// |
| /// ``` |
| /// use tokio::sync::OnceCell; |
| /// |
| /// static ONCE: OnceCell<u32> = OnceCell::const_new(); |
| /// |
| /// async fn get_global_integer() -> &'static u32 { |
| /// ONCE.get_or_init(|| async { |
| /// 1 + 1 |
| /// }).await |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let result = get_global_integer().await; |
| /// assert_eq!(*result, 2); |
| /// } |
| /// ``` |
| </span><span class="kw">pub struct </span>OnceCell<T> { |
| value_set: AtomicBool, |
| value: UnsafeCell<MaybeUninit<T>>, |
| semaphore: Semaphore, |
| } |
| |
| <span class="kw">impl</span><T> Default <span class="kw">for </span>OnceCell<T> { |
| <span class="kw">fn </span>default() -> OnceCell<T> { |
| OnceCell::new() |
| } |
| } |
| |
| <span class="kw">impl</span><T: fmt::Debug> fmt::Debug <span class="kw">for </span>OnceCell<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 { |
| fmt.debug_struct(<span class="string">"OnceCell"</span>) |
| .field(<span class="string">"value"</span>, <span class="kw-2">&</span><span class="self">self</span>.get()) |
| .finish() |
| } |
| } |
| |
| <span class="kw">impl</span><T: Clone> Clone <span class="kw">for </span>OnceCell<T> { |
| <span class="kw">fn </span>clone(<span class="kw-2">&</span><span class="self">self</span>) -> OnceCell<T> { |
| OnceCell::new_with(<span class="self">self</span>.get().cloned()) |
| } |
| } |
| |
| <span class="kw">impl</span><T: PartialEq> PartialEq <span class="kw">for </span>OnceCell<T> { |
| <span class="kw">fn </span>eq(<span class="kw-2">&</span><span class="self">self</span>, other: <span class="kw-2">&</span>OnceCell<T>) -> bool { |
| <span class="self">self</span>.get() == other.get() |
| } |
| } |
| |
| <span class="kw">impl</span><T: Eq> Eq <span class="kw">for </span>OnceCell<T> {} |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>OnceCell<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">if </span><span class="self">self</span>.initialized_mut() { |
| <span class="kw">unsafe </span>{ |
| <span class="self">self</span>.value |
| .with_mut(|ptr| ptr::drop_in_place((<span class="kw-2">*</span>ptr).as_mut_ptr())); |
| }; |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T> From<T> <span class="kw">for </span>OnceCell<T> { |
| <span class="kw">fn </span>from(value: T) -> <span class="self">Self </span>{ |
| <span class="kw">let </span>semaphore = Semaphore::new(<span class="number">0</span>); |
| semaphore.close(); |
| OnceCell { |
| value_set: AtomicBool::new(<span class="bool-val">true</span>), |
| value: UnsafeCell::new(MaybeUninit::new(value)), |
| semaphore, |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T> OnceCell<T> { |
| <span class="doccomment">/// Creates a new empty `OnceCell` instance. |
| </span><span class="kw">pub fn </span>new() -> <span class="self">Self </span>{ |
| OnceCell { |
| value_set: AtomicBool::new(<span class="bool-val">false</span>), |
| value: UnsafeCell::new(MaybeUninit::uninit()), |
| semaphore: Semaphore::new(<span class="number">1</span>), |
| } |
| } |
| |
| <span class="doccomment">/// Creates a new `OnceCell` that contains the provided value, if any. |
| /// |
| /// If the `Option` is `None`, this is equivalent to `OnceCell::new`. |
| /// |
| /// [`OnceCell::new`]: crate::sync::OnceCell::new |
| </span><span class="kw">pub fn </span>new_with(value: <span class="prelude-ty">Option</span><T>) -> <span class="self">Self </span>{ |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(v) = value { |
| OnceCell::from(v) |
| } <span class="kw">else </span>{ |
| OnceCell::new() |
| } |
| } |
| |
| <span class="doccomment">/// Creates a new empty `OnceCell` instance. |
| /// |
| /// Equivalent to `OnceCell::new`, except that it can be used in static |
| /// variables. |
| /// |
| /// # Example |
| /// |
| /// ``` |
| /// use tokio::sync::OnceCell; |
| /// |
| /// static ONCE: OnceCell<u32> = OnceCell::const_new(); |
| /// |
| /// async fn get_global_integer() -> &'static u32 { |
| /// ONCE.get_or_init(|| async { |
| /// 1 + 1 |
| /// }).await |
| /// } |
| /// |
| /// #[tokio::main] |
| /// async fn main() { |
| /// let result = get_global_integer().await; |
| /// assert_eq!(*result, 2); |
| /// } |
| /// ``` |
| </span><span class="attribute">#[cfg(all(feature = <span class="string">"parking_lot"</span>, not(all(loom, test))))] |
| #[cfg_attr(docsrs, doc(cfg(feature = <span class="string">"parking_lot"</span>)))] |
| </span><span class="kw">pub const fn </span>const_new() -> <span class="self">Self </span>{ |
| OnceCell { |
| value_set: AtomicBool::new(<span class="bool-val">false</span>), |
| value: UnsafeCell::new(MaybeUninit::uninit()), |
| semaphore: Semaphore::const_new(<span class="number">1</span>), |
| } |
| } |
| |
| <span class="doccomment">/// Returns `true` if the `OnceCell` currently contains a value, and `false` |
| /// otherwise. |
| </span><span class="kw">pub fn </span>initialized(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="comment">// Using acquire ordering so any threads that read a true from this |
| // atomic is able to read the value. |
| </span><span class="self">self</span>.value_set.load(Ordering::Acquire) |
| } |
| |
| <span class="doccomment">/// Returns `true` if the `OnceCell` currently contains a value, and `false` |
| /// otherwise. |
| </span><span class="kw">fn </span>initialized_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> bool { |
| <span class="kw-2">*</span><span class="self">self</span>.value_set.get_mut() |
| } |
| |
| <span class="comment">// SAFETY: The OnceCell must not be empty. |
| </span><span class="kw">unsafe fn </span>get_unchecked(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="kw-2">&*</span><span class="self">self</span>.value.with(|ptr| (<span class="kw-2">*</span>ptr).as_ptr()) |
| } |
| |
| <span class="comment">// SAFETY: The OnceCell must not be empty. |
| </span><span class="kw">unsafe fn </span>get_unchecked_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>T { |
| <span class="kw-2">&mut *</span><span class="self">self</span>.value.with_mut(|ptr| (<span class="kw-2">*</span>ptr).as_mut_ptr()) |
| } |
| |
| <span class="kw">fn </span>set_value(<span class="kw-2">&</span><span class="self">self</span>, value: T, permit: SemaphorePermit<<span class="lifetime">'_</span>>) -> <span class="kw-2">&</span>T { |
| <span class="comment">// SAFETY: We are holding the only permit on the semaphore. |
| </span><span class="kw">unsafe </span>{ |
| <span class="self">self</span>.value.with_mut(|ptr| (<span class="kw-2">*</span>ptr).as_mut_ptr().write(value)); |
| } |
| |
| <span class="comment">// Using release ordering so any threads that read a true from this |
| // atomic is able to read the value we just stored. |
| </span><span class="self">self</span>.value_set.store(<span class="bool-val">true</span>, Ordering::Release); |
| <span class="self">self</span>.semaphore.close(); |
| permit.forget(); |
| |
| <span class="comment">// SAFETY: We just initialized the cell. |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked() } |
| } |
| |
| <span class="doccomment">/// Returns a reference to the value currently stored in the `OnceCell`, or |
| /// `None` if the `OnceCell` is empty. |
| </span><span class="kw">pub fn </span>get(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="kw-2">&</span>T> { |
| <span class="kw">if </span><span class="self">self</span>.initialized() { |
| <span class="prelude-val">Some</span>(<span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked() }) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| |
| <span class="doccomment">/// Returns a mutable reference to the value currently stored in the |
| /// `OnceCell`, or `None` if the `OnceCell` is empty. |
| /// |
| /// Since this call borrows the `OnceCell` mutably, it is safe to mutate the |
| /// value inside the `OnceCell` — the mutable borrow statically guarantees |
| /// no other references exist. |
| </span><span class="kw">pub fn </span>get_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><<span class="kw-2">&mut </span>T> { |
| <span class="kw">if </span><span class="self">self</span>.initialized_mut() { |
| <span class="prelude-val">Some</span>(<span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked_mut() }) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| |
| <span class="doccomment">/// Sets the value of the `OnceCell` to the given value if the `OnceCell` is |
| /// empty. |
| /// |
| /// If the `OnceCell` already has a value, this call will fail with an |
| /// [`SetError::AlreadyInitializedError`]. |
| /// |
| /// If the `OnceCell` is empty, but some other task is currently trying to |
| /// set the value, this call will fail with [`SetError::InitializingError`]. |
| /// |
| /// [`SetError::AlreadyInitializedError`]: crate::sync::SetError::AlreadyInitializedError |
| /// [`SetError::InitializingError`]: crate::sync::SetError::InitializingError |
| </span><span class="kw">pub fn </span>set(<span class="kw-2">&</span><span class="self">self</span>, value: T) -> <span class="prelude-ty">Result</span><(), SetError<T>> { |
| <span class="kw">if </span><span class="self">self</span>.initialized() { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(SetError::AlreadyInitializedError(value)); |
| } |
| |
| <span class="comment">// Another task might be initializing the cell, in which case |
| // `try_acquire` will return an error. If we succeed to acquire the |
| // permit, then we can set the value. |
| </span><span class="kw">match </span><span class="self">self</span>.semaphore.try_acquire() { |
| <span class="prelude-val">Ok</span>(permit) => { |
| <span class="macro">debug_assert!</span>(!<span class="self">self</span>.initialized()); |
| <span class="self">self</span>.set_value(value, permit); |
| <span class="prelude-val">Ok</span>(()) |
| } |
| <span class="prelude-val">Err</span>(TryAcquireError::NoPermits) => { |
| <span class="comment">// Some other task is holding the permit. That task is |
| // currently trying to initialize the value. |
| </span><span class="prelude-val">Err</span>(SetError::InitializingError(value)) |
| } |
| <span class="prelude-val">Err</span>(TryAcquireError::Closed) => { |
| <span class="comment">// The semaphore was closed. Some other task has initialized |
| // the value. |
| </span><span class="prelude-val">Err</span>(SetError::AlreadyInitializedError(value)) |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Gets the value currently in the `OnceCell`, or initialize it with the |
| /// given asynchronous operation. |
| /// |
| /// If some other task is currently working on initializing the `OnceCell`, |
| /// this call will wait for that other task to finish, then return the value |
| /// that the other task produced. |
| /// |
| /// If the provided operation is cancelled or panics, the initialization |
| /// attempt is cancelled. If there are other tasks waiting for the value to |
| /// be initialized, one of them will start another attempt at initializing |
| /// the value. |
| /// |
| /// This will deadlock if `f` tries to initialize the cell recursively. |
| </span><span class="kw">pub async fn </span>get_or_init<F, Fut>(<span class="kw-2">&</span><span class="self">self</span>, f: F) -> <span class="kw-2">&</span>T |
| <span class="kw">where |
| </span>F: FnOnce() -> Fut, |
| Fut: Future<Output = T>, |
| { |
| <span class="kw">if </span><span class="self">self</span>.initialized() { |
| <span class="comment">// SAFETY: The OnceCell has been fully initialized. |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked() } |
| } <span class="kw">else </span>{ |
| <span class="comment">// Here we try to acquire the semaphore permit. Holding the permit |
| // will allow us to set the value of the OnceCell, and prevents |
| // other tasks from initializing the OnceCell while we are holding |
| // it. |
| </span><span class="kw">match </span><span class="self">self</span>.semaphore.acquire().<span class="kw">await </span>{ |
| <span class="prelude-val">Ok</span>(permit) => { |
| <span class="macro">debug_assert!</span>(!<span class="self">self</span>.initialized()); |
| |
| <span class="comment">// If `f()` panics or `select!` is called, this |
| // `get_or_init` call is aborted and the semaphore permit is |
| // dropped. |
| </span><span class="kw">let </span>value = f().<span class="kw">await</span>; |
| |
| <span class="self">self</span>.set_value(value, permit) |
| } |
| <span class="prelude-val">Err</span>(<span class="kw">_</span>) => { |
| <span class="macro">debug_assert!</span>(<span class="self">self</span>.initialized()); |
| |
| <span class="comment">// SAFETY: The semaphore has been closed. This only happens |
| // when the OnceCell is fully initialized. |
| </span><span class="kw">unsafe </span>{ <span class="self">self</span>.get_unchecked() } |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Gets the value currently in the `OnceCell`, or initialize it with the |
| /// given asynchronous operation. |
| /// |
| /// If some other task is currently working on initializing the `OnceCell`, |
| /// this call will wait for that other task to finish, then return the value |
| /// that the other task produced. |
| /// |
| /// If the provided operation returns an error, is cancelled or panics, the |
| /// initialization attempt is cancelled. If there are other tasks waiting |
| /// for the value to be initialized, one of them will start another attempt |
| /// at initializing the value. |
| /// |
| /// This will deadlock if `f` tries to initialize the cell recursively. |
| </span><span class="kw">pub async fn </span>get_or_try_init<E, F, Fut>(<span class="kw-2">&</span><span class="self">self</span>, f: F) -> <span class="prelude-ty">Result</span><<span class="kw-2">&</span>T, E> |
| <span class="kw">where |
| </span>F: FnOnce() -> Fut, |
| Fut: Future<Output = <span class="prelude-ty">Result</span><T, E>>, |
| { |
| <span class="kw">if </span><span class="self">self</span>.initialized() { |
| <span class="comment">// SAFETY: The OnceCell has been fully initialized. |
| </span><span class="kw">unsafe </span>{ <span class="prelude-val">Ok</span>(<span class="self">self</span>.get_unchecked()) } |
| } <span class="kw">else </span>{ |
| <span class="comment">// Here we try to acquire the semaphore permit. Holding the permit |
| // will allow us to set the value of the OnceCell, and prevents |
| // other tasks from initializing the OnceCell while we are holding |
| // it. |
| </span><span class="kw">match </span><span class="self">self</span>.semaphore.acquire().<span class="kw">await </span>{ |
| <span class="prelude-val">Ok</span>(permit) => { |
| <span class="macro">debug_assert!</span>(!<span class="self">self</span>.initialized()); |
| |
| <span class="comment">// If `f()` panics or `select!` is called, this |
| // `get_or_try_init` call is aborted and the semaphore |
| // permit is dropped. |
| </span><span class="kw">let </span>value = f().<span class="kw">await</span>; |
| |
| <span class="kw">match </span>value { |
| <span class="prelude-val">Ok</span>(value) => <span class="prelude-val">Ok</span>(<span class="self">self</span>.set_value(value, permit)), |
| <span class="prelude-val">Err</span>(e) => <span class="prelude-val">Err</span>(e), |
| } |
| } |
| <span class="prelude-val">Err</span>(<span class="kw">_</span>) => { |
| <span class="macro">debug_assert!</span>(<span class="self">self</span>.initialized()); |
| |
| <span class="comment">// SAFETY: The semaphore has been closed. This only happens |
| // when the OnceCell is fully initialized. |
| </span><span class="kw">unsafe </span>{ <span class="prelude-val">Ok</span>(<span class="self">self</span>.get_unchecked()) } |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Takes the value from the cell, destroying the cell in the process. |
| /// Returns `None` if the cell is empty. |
| </span><span class="kw">pub fn </span>into_inner(<span class="kw-2">mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><T> { |
| <span class="kw">if </span><span class="self">self</span>.initialized_mut() { |
| <span class="comment">// Set to uninitialized for the destructor of `OnceCell` to work properly |
| </span><span class="kw-2">*</span><span class="self">self</span>.value_set.get_mut() = <span class="bool-val">false</span>; |
| <span class="prelude-val">Some</span>(<span class="kw">unsafe </span>{ <span class="self">self</span>.value.with(|ptr| ptr::read(ptr).assume_init()) }) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| |
| <span class="doccomment">/// Takes ownership of the current value, leaving the cell empty. Returns |
| /// `None` if the cell is empty. |
| </span><span class="kw">pub fn </span>take(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><T> { |
| std::mem::take(<span class="self">self</span>).into_inner() |
| } |
| } |
| |
| <span class="comment">// Since `get` gives us access to immutable references of the OnceCell, OnceCell |
| // can only be Sync if T is Sync, otherwise OnceCell would allow sharing |
| // references of !Sync values across threads. We need T to be Send in order for |
| // OnceCell to by Sync because we can use `set` on `&OnceCell<T>` to send values |
| // (of type T) across threads. |
| </span><span class="kw">unsafe impl</span><T: Sync + Send> Sync <span class="kw">for </span>OnceCell<T> {} |
| |
| <span class="comment">// Access to OnceCell's value is guarded by the semaphore permit |
| // and atomic operations on `value_set`, so as long as T itself is Send |
| // it's safe to send it to another thread |
| </span><span class="kw">unsafe impl</span><T: Send> Send <span class="kw">for </span>OnceCell<T> {} |
| |
| <span class="doccomment">/// Errors that can be returned from [`OnceCell::set`]. |
| /// |
| /// [`OnceCell::set`]: crate::sync::OnceCell::set |
| </span><span class="attribute">#[derive(Debug, PartialEq, Eq)] |
| </span><span class="kw">pub enum </span>SetError<T> { |
| <span class="doccomment">/// The cell was already initialized when [`OnceCell::set`] was called. |
| /// |
| /// [`OnceCell::set`]: crate::sync::OnceCell::set |
| </span>AlreadyInitializedError(T), |
| |
| <span class="doccomment">/// The cell is currently being initialized. |
| </span>InitializingError(T), |
| } |
| |
| <span class="kw">impl</span><T> fmt::Display <span class="kw">for </span>SetError<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">match </span><span class="self">self </span>{ |
| SetError::AlreadyInitializedError(<span class="kw">_</span>) => <span class="macro">write!</span>(f, <span class="string">"AlreadyInitializedError"</span>), |
| SetError::InitializingError(<span class="kw">_</span>) => <span class="macro">write!</span>(f, <span class="string">"InitializingError"</span>), |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T: fmt::Debug> Error <span class="kw">for </span>SetError<T> {} |
| |
| <span class="kw">impl</span><T> SetError<T> { |
| <span class="doccomment">/// Whether `SetError` is `SetError::AlreadyInitializedError`. |
| </span><span class="kw">pub fn </span>is_already_init_err(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">match </span><span class="self">self </span>{ |
| SetError::AlreadyInitializedError(<span class="kw">_</span>) => <span class="bool-val">true</span>, |
| SetError::InitializingError(<span class="kw">_</span>) => <span class="bool-val">false</span>, |
| } |
| } |
| |
| <span class="doccomment">/// Whether `SetError` is `SetError::InitializingError` |
| </span><span class="kw">pub fn </span>is_initializing_err(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">match </span><span class="self">self </span>{ |
| SetError::AlreadyInitializedError(<span class="kw">_</span>) => <span class="bool-val">false</span>, |
| SetError::InitializingError(<span class="kw">_</span>) => <span class="bool-val">true</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> |
