| <!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/once_cell-1.18.0/src/imp_std.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>imp_std.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="../../once_cell/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="../../once_cell/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="comment">// There's a lot of scary concurrent code in this module, but it is copied from |
| // `std::sync::Once` with two changes: |
| // * no poisoning |
| // * init function can fail |
| |
| </span><span class="kw">use </span>std::{ |
| cell::{Cell, UnsafeCell}, |
| panic::{RefUnwindSafe, UnwindSafe}, |
| sync::atomic::{AtomicBool, AtomicPtr, Ordering}, |
| thread::{<span class="self">self</span>, Thread}, |
| }; |
| |
| <span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>OnceCell<T> { |
| <span class="comment">// This `queue` field is the core of the implementation. It encodes two |
| // pieces of information: |
| // |
| // * The current state of the cell (`INCOMPLETE`, `RUNNING`, `COMPLETE`) |
| // * Linked list of threads waiting for the current cell. |
| // |
| // State is encoded in two low bits. Only `INCOMPLETE` and `RUNNING` states |
| // allow waiters. |
| </span>queue: AtomicPtr<Waiter>, |
| value: UnsafeCell<<span class="prelude-ty">Option</span><T>>, |
| } |
| |
| <span class="comment">// Why do we need `T: Send`? |
| // Thread A creates a `OnceCell` and shares it with |
| // scoped thread B, which fills the cell, which is |
| // then destroyed by A. That is, destructor observes |
| // a sent value. |
| </span><span class="kw">unsafe impl</span><T: Sync + Send> Sync <span class="kw">for </span>OnceCell<T> {} |
| <span class="kw">unsafe impl</span><T: Send> Send <span class="kw">for </span>OnceCell<T> {} |
| |
| <span class="kw">impl</span><T: RefUnwindSafe + UnwindSafe> RefUnwindSafe <span class="kw">for </span>OnceCell<T> {} |
| <span class="kw">impl</span><T: UnwindSafe> UnwindSafe <span class="kw">for </span>OnceCell<T> {} |
| |
| <span class="kw">impl</span><T> OnceCell<T> { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">const fn </span>new() -> OnceCell<T> { |
| OnceCell { queue: AtomicPtr::new(INCOMPLETE_PTR), value: UnsafeCell::new(<span class="prelude-val">None</span>) } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">const fn </span>with_value(value: T) -> OnceCell<T> { |
| OnceCell { queue: AtomicPtr::new(COMPLETE_PTR), value: UnsafeCell::new(<span class="prelude-val">Some</span>(value)) } |
| } |
| |
| <span class="doccomment">/// Safety: synchronizes with store to value via Release/(Acquire|SeqCst). |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>is_initialized(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="comment">// An `Acquire` load is enough because that makes all the initialization |
| // operations visible to us, and, this being a fast path, weaker |
| // ordering helps with performance. This `Acquire` synchronizes with |
| // `SeqCst` operations on the slow path. |
| </span><span class="self">self</span>.queue.load(Ordering::Acquire) == COMPLETE_PTR |
| } |
| |
| <span class="doccomment">/// Safety: synchronizes with store to value via SeqCst read from state, |
| /// writes value only once because we never get to INCOMPLETE state after a |
| /// successful write. |
| </span><span class="attribute">#[cold] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>initialize<F, E>(<span class="kw-2">&</span><span class="self">self</span>, f: F) -> <span class="prelude-ty">Result</span><(), E> |
| <span class="kw">where |
| </span>F: FnOnce() -> <span class="prelude-ty">Result</span><T, E>, |
| { |
| <span class="kw">let </span><span class="kw-2">mut </span>f = <span class="prelude-val">Some</span>(f); |
| <span class="kw">let </span><span class="kw-2">mut </span>res: <span class="prelude-ty">Result</span><(), E> = <span class="prelude-val">Ok</span>(()); |
| <span class="kw">let </span>slot: <span class="kw-2">*mut </span><span class="prelude-ty">Option</span><T> = <span class="self">self</span>.value.get(); |
| initialize_or_wait( |
| <span class="kw-2">&</span><span class="self">self</span>.queue, |
| <span class="prelude-val">Some</span>(<span class="kw-2">&mut </span>|| { |
| <span class="kw">let </span>f = <span class="kw">unsafe </span>{ f.take().unwrap_unchecked() }; |
| <span class="kw">match </span>f() { |
| <span class="prelude-val">Ok</span>(value) => { |
| <span class="kw">unsafe </span>{ <span class="kw-2">*</span>slot = <span class="prelude-val">Some</span>(value) }; |
| <span class="bool-val">true |
| </span>} |
| <span class="prelude-val">Err</span>(err) => { |
| res = <span class="prelude-val">Err</span>(err); |
| <span class="bool-val">false |
| </span>} |
| } |
| }), |
| ); |
| res |
| } |
| |
| <span class="attribute">#[cold] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>wait(<span class="kw-2">&</span><span class="self">self</span>) { |
| initialize_or_wait(<span class="kw-2">&</span><span class="self">self</span>.queue, <span class="prelude-val">None</span>); |
| } |
| |
| <span class="doccomment">/// Get the reference to the underlying value, without checking if the cell |
| /// is initialized. |
| /// |
| /// # Safety |
| /// |
| /// Caller must ensure that the cell is in initialized state, and that |
| /// the contents are acquired by (synchronized to) this thread. |
| </span><span class="kw">pub</span>(<span class="kw">crate</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="macro">debug_assert!</span>(<span class="self">self</span>.is_initialized()); |
| <span class="kw">let </span>slot = <span class="kw-2">&*</span><span class="self">self</span>.value.get(); |
| slot.as_ref().unwrap_unchecked() |
| } |
| |
| <span class="doccomment">/// Gets the mutable reference to the underlying value. |
| /// Returns `None` if the cell is empty. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">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="comment">// Safe b/c we have a unique access. |
| </span><span class="kw">unsafe </span>{ <span class="kw-2">&mut *</span><span class="self">self</span>.value.get() }.as_mut() |
| } |
| |
| <span class="doccomment">/// Consumes this `OnceCell`, returning the wrapped value. |
| /// Returns `None` if the cell was empty. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>into_inner(<span class="self">self</span>) -> <span class="prelude-ty">Option</span><T> { |
| <span class="comment">// Because `into_inner` takes `self` by value, the compiler statically |
| // verifies that it is not currently borrowed. |
| // So, it is safe to move out `Option<T>`. |
| </span><span class="self">self</span>.value.into_inner() |
| } |
| } |
| |
| <span class="comment">// Three states that a OnceCell can be in, encoded into the lower bits of `queue` in |
| // the OnceCell structure. |
| </span><span class="kw">const </span>INCOMPLETE: usize = <span class="number">0x0</span>; |
| <span class="kw">const </span>RUNNING: usize = <span class="number">0x1</span>; |
| <span class="kw">const </span>COMPLETE: usize = <span class="number">0x2</span>; |
| <span class="kw">const </span>INCOMPLETE_PTR: <span class="kw-2">*mut </span>Waiter = INCOMPLETE <span class="kw">as </span><span class="kw-2">*mut </span>Waiter; |
| <span class="kw">const </span>COMPLETE_PTR: <span class="kw-2">*mut </span>Waiter = COMPLETE <span class="kw">as </span><span class="kw-2">*mut </span>Waiter; |
| |
| <span class="comment">// Mask to learn about the state. All other bits are the queue of waiters if |
| // this is in the RUNNING state. |
| </span><span class="kw">const </span>STATE_MASK: usize = <span class="number">0x3</span>; |
| |
| <span class="doccomment">/// Representation of a node in the linked list of waiters in the RUNNING state. |
| /// A waiters is stored on the stack of the waiting threads. |
| </span><span class="attribute">#[repr(align(<span class="number">4</span>))] </span><span class="comment">// Ensure the two lower bits are free to use as state bits. |
| </span><span class="kw">struct </span>Waiter { |
| thread: Cell<<span class="prelude-ty">Option</span><Thread>>, |
| signaled: AtomicBool, |
| next: <span class="kw-2">*mut </span>Waiter, |
| } |
| |
| <span class="doccomment">/// Drains and notifies the queue of waiters on drop. |
| </span><span class="kw">struct </span>Guard<<span class="lifetime">'a</span>> { |
| queue: <span class="kw-2">&</span><span class="lifetime">'a </span>AtomicPtr<Waiter>, |
| new_queue: <span class="kw-2">*mut </span>Waiter, |
| } |
| |
| <span class="kw">impl </span>Drop <span class="kw">for </span>Guard<<span class="lifetime">'_</span>> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">let </span>queue = <span class="self">self</span>.queue.swap(<span class="self">self</span>.new_queue, Ordering::AcqRel); |
| |
| <span class="kw">let </span>state = strict::addr(queue) & STATE_MASK; |
| <span class="macro">assert_eq!</span>(state, RUNNING); |
| |
| <span class="kw">unsafe </span>{ |
| <span class="kw">let </span><span class="kw-2">mut </span>waiter = strict::map_addr(queue, |q| q & !STATE_MASK); |
| <span class="kw">while </span>!waiter.is_null() { |
| <span class="kw">let </span>next = (<span class="kw-2">*</span>waiter).next; |
| <span class="kw">let </span>thread = (<span class="kw-2">*</span>waiter).thread.take().unwrap(); |
| (<span class="kw-2">*</span>waiter).signaled.store(<span class="bool-val">true</span>, Ordering::Release); |
| waiter = next; |
| thread.unpark(); |
| } |
| } |
| } |
| } |
| |
| <span class="comment">// Corresponds to `std::sync::Once::call_inner`. |
| // |
| // Originally copied from std, but since modified to remove poisoning and to |
| // support wait. |
| // |
| // Note: this is intentionally monomorphic |
| </span><span class="attribute">#[inline(never)] |
| </span><span class="kw">fn </span>initialize_or_wait(queue: <span class="kw-2">&</span>AtomicPtr<Waiter>, <span class="kw-2">mut </span>init: <span class="prelude-ty">Option</span><<span class="kw-2">&mut </span><span class="kw">dyn </span>FnMut() -> bool>) { |
| <span class="kw">let </span><span class="kw-2">mut </span>curr_queue = queue.load(Ordering::Acquire); |
| |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>curr_state = strict::addr(curr_queue) & STATE_MASK; |
| <span class="kw">match </span>(curr_state, <span class="kw-2">&mut </span>init) { |
| (COMPLETE, <span class="kw">_</span>) => <span class="kw">return</span>, |
| (INCOMPLETE, <span class="prelude-val">Some</span>(init)) => { |
| <span class="kw">let </span>exchange = queue.compare_exchange( |
| curr_queue, |
| strict::map_addr(curr_queue, |q| (q & !STATE_MASK) | RUNNING), |
| Ordering::Acquire, |
| Ordering::Acquire, |
| ); |
| <span class="kw">if let </span><span class="prelude-val">Err</span>(new_queue) = exchange { |
| curr_queue = new_queue; |
| <span class="kw">continue</span>; |
| } |
| <span class="kw">let </span><span class="kw-2">mut </span>guard = Guard { queue, new_queue: INCOMPLETE_PTR }; |
| <span class="kw">if </span>init() { |
| guard.new_queue = COMPLETE_PTR; |
| } |
| <span class="kw">return</span>; |
| } |
| (INCOMPLETE, <span class="prelude-val">None</span>) | (RUNNING, <span class="kw">_</span>) => { |
| wait(queue, curr_queue); |
| curr_queue = queue.load(Ordering::Acquire); |
| } |
| <span class="kw">_ </span>=> <span class="macro">debug_assert!</span>(<span class="bool-val">false</span>), |
| } |
| } |
| } |
| |
| <span class="kw">fn </span>wait(queue: <span class="kw-2">&</span>AtomicPtr<Waiter>, <span class="kw-2">mut </span>curr_queue: <span class="kw-2">*mut </span>Waiter) { |
| <span class="kw">let </span>curr_state = strict::addr(curr_queue) & STATE_MASK; |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>node = Waiter { |
| thread: Cell::new(<span class="prelude-val">Some</span>(thread::current())), |
| signaled: AtomicBool::new(<span class="bool-val">false</span>), |
| next: strict::map_addr(curr_queue, |q| q & !STATE_MASK), |
| }; |
| <span class="kw">let </span>me = <span class="kw-2">&</span>node <span class="kw">as </span><span class="kw-2">*const </span>Waiter <span class="kw">as </span><span class="kw-2">*mut </span>Waiter; |
| |
| <span class="kw">let </span>exchange = queue.compare_exchange( |
| curr_queue, |
| strict::map_addr(me, |q| q | curr_state), |
| Ordering::Release, |
| Ordering::Relaxed, |
| ); |
| <span class="kw">if let </span><span class="prelude-val">Err</span>(new_queue) = exchange { |
| <span class="kw">if </span>strict::addr(new_queue) & STATE_MASK != curr_state { |
| <span class="kw">return</span>; |
| } |
| curr_queue = new_queue; |
| <span class="kw">continue</span>; |
| } |
| |
| <span class="kw">while </span>!node.signaled.load(Ordering::Acquire) { |
| thread::park(); |
| } |
| <span class="kw">break</span>; |
| } |
| } |
| |
| <span class="comment">// Polyfill of strict provenance from https://crates.io/crates/sptr. |
| // |
| // Use free-standing function rather than a trait to keep things simple and |
| // avoid any potential conflicts with future stabile std API. |
| </span><span class="kw">mod </span>strict { |
| <span class="attribute">#[must_use] |
| #[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>addr<T>(ptr: <span class="kw-2">*mut </span>T) -> usize |
| <span class="kw">where |
| </span>T: Sized, |
| { |
| <span class="comment">// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic. |
| // SAFETY: Pointer-to-integer transmutes are valid (if you are okay with losing the |
| // provenance). |
| </span><span class="kw">unsafe </span>{ core::mem::transmute(ptr) } |
| } |
| |
| <span class="attribute">#[must_use] |
| #[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>with_addr<T>(ptr: <span class="kw-2">*mut </span>T, addr: usize) -> <span class="kw-2">*mut </span>T |
| <span class="kw">where |
| </span>T: Sized, |
| { |
| <span class="comment">// FIXME(strict_provenance_magic): I am magic and should be a compiler intrinsic. |
| // |
| // In the mean-time, this operation is defined to be "as if" it was |
| // a wrapping_offset, so we can emulate it as such. This should properly |
| // restore pointer provenance even under today's compiler. |
| </span><span class="kw">let </span>self_addr = <span class="self">self</span>::addr(ptr) <span class="kw">as </span>isize; |
| <span class="kw">let </span>dest_addr = addr <span class="kw">as </span>isize; |
| <span class="kw">let </span>offset = dest_addr.wrapping_sub(self_addr); |
| |
| <span class="comment">// This is the canonical desugarring of this operation, |
| // but `pointer::cast` was only stabilized in 1.38. |
| // self.cast::<u8>().wrapping_offset(offset).cast::<T>() |
| </span>(ptr <span class="kw">as </span><span class="kw-2">*mut </span>u8).wrapping_offset(offset) <span class="kw">as </span><span class="kw-2">*mut </span>T |
| } |
| |
| <span class="attribute">#[must_use] |
| #[inline] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>map_addr<T>(ptr: <span class="kw-2">*mut </span>T, f: <span class="kw">impl </span>FnOnce(usize) -> usize) -> <span class="kw-2">*mut </span>T |
| <span class="kw">where |
| </span>T: Sized, |
| { |
| <span class="self">self</span>::with_addr(ptr, f(addr(ptr))) |
| } |
| } |
| |
| <span class="comment">// These test are snatched from std as well. |
| </span><span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| <span class="kw">use </span>std::panic; |
| <span class="kw">use </span>std::{sync::mpsc::channel, thread}; |
| |
| <span class="kw">use </span><span class="kw">super</span>::OnceCell; |
| |
| <span class="kw">impl</span><T> OnceCell<T> { |
| <span class="kw">fn </span>init(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw">impl </span>FnOnce() -> T) { |
| <span class="kw">enum </span>Void {} |
| <span class="kw">let _ </span>= <span class="self">self</span>.initialize(|| <span class="prelude-val">Ok</span>::<T, Void>(f())); |
| } |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>smoke_once() { |
| <span class="kw">static </span>O: OnceCell<()> = OnceCell::new(); |
| <span class="kw">let </span><span class="kw-2">mut </span>a = <span class="number">0</span>; |
| O.init(|| a += <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(a, <span class="number">1</span>); |
| O.init(|| a += <span class="number">1</span>); |
| <span class="macro">assert_eq!</span>(a, <span class="number">1</span>); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>stampede_once() { |
| <span class="kw">static </span>O: OnceCell<()> = OnceCell::new(); |
| <span class="kw">static </span><span class="kw-2">mut </span>RUN: bool = <span class="bool-val">false</span>; |
| |
| <span class="kw">let </span>(tx, rx) = channel(); |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| <span class="kw">let </span>tx = tx.clone(); |
| thread::spawn(<span class="kw">move </span>|| { |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">4 </span>{ |
| thread::yield_now() |
| } |
| <span class="kw">unsafe </span>{ |
| O.init(|| { |
| <span class="macro">assert!</span>(!RUN); |
| RUN = <span class="bool-val">true</span>; |
| }); |
| <span class="macro">assert!</span>(RUN); |
| } |
| tx.send(()).unwrap(); |
| }); |
| } |
| |
| <span class="kw">unsafe </span>{ |
| O.init(|| { |
| <span class="macro">assert!</span>(!RUN); |
| RUN = <span class="bool-val">true</span>; |
| }); |
| <span class="macro">assert!</span>(RUN); |
| } |
| |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| rx.recv().unwrap(); |
| } |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>poison_bad() { |
| <span class="kw">static </span>O: OnceCell<()> = OnceCell::new(); |
| |
| <span class="comment">// poison the once |
| </span><span class="kw">let </span>t = panic::catch_unwind(|| { |
| O.init(|| <span class="macro">panic!</span>()); |
| }); |
| <span class="macro">assert!</span>(t.is_err()); |
| |
| <span class="comment">// we can subvert poisoning, however |
| </span><span class="kw">let </span><span class="kw-2">mut </span>called = <span class="bool-val">false</span>; |
| O.init(|| { |
| called = <span class="bool-val">true</span>; |
| }); |
| <span class="macro">assert!</span>(called); |
| |
| <span class="comment">// once any success happens, we stop propagating the poison |
| </span>O.init(|| {}); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>wait_for_force_to_finish() { |
| <span class="kw">static </span>O: OnceCell<()> = OnceCell::new(); |
| |
| <span class="comment">// poison the once |
| </span><span class="kw">let </span>t = panic::catch_unwind(|| { |
| O.init(|| <span class="macro">panic!</span>()); |
| }); |
| <span class="macro">assert!</span>(t.is_err()); |
| |
| <span class="comment">// make sure someone's waiting inside the once via a force |
| </span><span class="kw">let </span>(tx1, rx1) = channel(); |
| <span class="kw">let </span>(tx2, rx2) = channel(); |
| <span class="kw">let </span>t1 = thread::spawn(<span class="kw">move </span>|| { |
| O.init(|| { |
| tx1.send(()).unwrap(); |
| rx2.recv().unwrap(); |
| }); |
| }); |
| |
| rx1.recv().unwrap(); |
| |
| <span class="comment">// put another waiter on the once |
| </span><span class="kw">let </span>t2 = thread::spawn(|| { |
| <span class="kw">let </span><span class="kw-2">mut </span>called = <span class="bool-val">false</span>; |
| O.init(|| { |
| called = <span class="bool-val">true</span>; |
| }); |
| <span class="macro">assert!</span>(!called); |
| }); |
| |
| tx2.send(()).unwrap(); |
| |
| <span class="macro">assert!</span>(t1.join().is_ok()); |
| <span class="macro">assert!</span>(t2.join().is_ok()); |
| } |
| |
| <span class="attribute">#[test] |
| #[cfg(target_pointer_width = <span class="string">"64"</span>)] |
| </span><span class="kw">fn </span>test_size() { |
| <span class="kw">use </span>std::mem::size_of; |
| |
| <span class="macro">assert_eq!</span>(size_of::<OnceCell<u32>>(), <span class="number">4 </span>* size_of::<u32>()); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="once_cell" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
