| <!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/crossbeam-channel-0.5.8/src/flavors/list.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>list.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="../../../crossbeam_channel/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="../../../crossbeam_channel/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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| <span id="756">756</span> |
| </pre><pre class="rust"><code><span class="doccomment">//! Unbounded channel implemented as a linked list. |
| |
| </span><span class="kw">use </span>std::cell::UnsafeCell; |
| <span class="kw">use </span>std::marker::PhantomData; |
| <span class="kw">use </span>std::mem::MaybeUninit; |
| <span class="kw">use </span>std::ptr; |
| <span class="kw">use </span>std::sync::atomic::{<span class="self">self</span>, AtomicPtr, AtomicUsize, Ordering}; |
| <span class="kw">use </span>std::time::Instant; |
| |
| <span class="kw">use </span>crossbeam_utils::{Backoff, CachePadded}; |
| |
| <span class="kw">use </span><span class="kw">crate</span>::context::Context; |
| <span class="kw">use </span><span class="kw">crate</span>::err::{RecvTimeoutError, SendTimeoutError, TryRecvError, TrySendError}; |
| <span class="kw">use </span><span class="kw">crate</span>::select::{Operation, SelectHandle, Selected, Token}; |
| <span class="kw">use </span><span class="kw">crate</span>::waker::SyncWaker; |
| |
| <span class="comment">// TODO(stjepang): Once we bump the minimum required Rust version to 1.28 or newer, re-apply the |
| // following changes by @kleimkuhler: |
| // |
| // 1. https://github.com/crossbeam-rs/crossbeam-channel/pull/100 |
| // 2. https://github.com/crossbeam-rs/crossbeam-channel/pull/101 |
| |
| // Bits indicating the state of a slot: |
| // * If a message has been written into the slot, `WRITE` is set. |
| // * If a message has been read from the slot, `READ` is set. |
| // * If the block is being destroyed, `DESTROY` is set. |
| </span><span class="kw">const </span>WRITE: usize = <span class="number">1</span>; |
| <span class="kw">const </span>READ: usize = <span class="number">2</span>; |
| <span class="kw">const </span>DESTROY: usize = <span class="number">4</span>; |
| |
| <span class="comment">// Each block covers one "lap" of indices. |
| </span><span class="kw">const </span>LAP: usize = <span class="number">32</span>; |
| <span class="comment">// The maximum number of messages a block can hold. |
| </span><span class="kw">const </span>BLOCK_CAP: usize = LAP - <span class="number">1</span>; |
| <span class="comment">// How many lower bits are reserved for metadata. |
| </span><span class="kw">const </span>SHIFT: usize = <span class="number">1</span>; |
| <span class="comment">// Has two different purposes: |
| // * If set in head, indicates that the block is not the last one. |
| // * If set in tail, indicates that the channel is disconnected. |
| </span><span class="kw">const </span>MARK_BIT: usize = <span class="number">1</span>; |
| |
| <span class="doccomment">/// A slot in a block. |
| </span><span class="kw">struct </span>Slot<T> { |
| <span class="doccomment">/// The message. |
| </span>msg: UnsafeCell<MaybeUninit<T>>, |
| |
| <span class="doccomment">/// The state of the slot. |
| </span>state: AtomicUsize, |
| } |
| |
| <span class="kw">impl</span><T> Slot<T> { |
| <span class="kw">const </span>UNINIT: <span class="self">Self </span>= <span class="self">Self </span>{ |
| msg: UnsafeCell::new(MaybeUninit::uninit()), |
| state: AtomicUsize::new(<span class="number">0</span>), |
| }; |
| |
| <span class="doccomment">/// Waits until a message is written into the slot. |
| </span><span class="kw">fn </span>wait_write(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">while </span><span class="self">self</span>.state.load(Ordering::Acquire) & WRITE == <span class="number">0 </span>{ |
| backoff.snooze(); |
| } |
| } |
| } |
| |
| <span class="doccomment">/// A block in a linked list. |
| /// |
| /// Each block in the list can hold up to `BLOCK_CAP` messages. |
| </span><span class="kw">struct </span>Block<T> { |
| <span class="doccomment">/// The next block in the linked list. |
| </span>next: AtomicPtr<Block<T>>, |
| |
| <span class="doccomment">/// Slots for messages. |
| </span>slots: [Slot<T>; BLOCK_CAP], |
| } |
| |
| <span class="kw">impl</span><T> Block<T> { |
| <span class="doccomment">/// Creates an empty block. |
| </span><span class="kw">fn </span>new() -> Block<T> { |
| <span class="self">Self </span>{ |
| next: AtomicPtr::new(ptr::null_mut()), |
| slots: [Slot::UNINIT; BLOCK_CAP], |
| } |
| } |
| |
| <span class="doccomment">/// Waits until the next pointer is set. |
| </span><span class="kw">fn </span>wait_next(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">*mut </span>Block<T> { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>next = <span class="self">self</span>.next.load(Ordering::Acquire); |
| <span class="kw">if </span>!next.is_null() { |
| <span class="kw">return </span>next; |
| } |
| backoff.snooze(); |
| } |
| } |
| |
| <span class="doccomment">/// Sets the `DESTROY` bit in slots starting from `start` and destroys the block. |
| </span><span class="kw">unsafe fn </span>destroy(this: <span class="kw-2">*mut </span>Block<T>, start: usize) { |
| <span class="comment">// It is not necessary to set the `DESTROY` bit in the last slot because that slot has |
| // begun destruction of the block. |
| </span><span class="kw">for </span>i <span class="kw">in </span>start..BLOCK_CAP - <span class="number">1 </span>{ |
| <span class="kw">let </span>slot = (<span class="kw-2">*</span>this).slots.get_unchecked(i); |
| |
| <span class="comment">// Mark the `DESTROY` bit if a thread is still using the slot. |
| </span><span class="kw">if </span>slot.state.load(Ordering::Acquire) & READ == <span class="number">0 |
| </span>&& slot.state.fetch_or(DESTROY, Ordering::AcqRel) & READ == <span class="number">0 |
| </span>{ |
| <span class="comment">// If a thread is still using the slot, it will continue destruction of the block. |
| </span><span class="kw">return</span>; |
| } |
| } |
| |
| <span class="comment">// No thread is using the block, now it is safe to destroy it. |
| </span>drop(Box::from_raw(this)); |
| } |
| } |
| |
| <span class="doccomment">/// A position in a channel. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">struct </span>Position<T> { |
| <span class="doccomment">/// The index in the channel. |
| </span>index: AtomicUsize, |
| |
| <span class="doccomment">/// The block in the linked list. |
| </span>block: AtomicPtr<Block<T>>, |
| } |
| |
| <span class="doccomment">/// The token type for the list flavor. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>ListToken { |
| <span class="doccomment">/// The block of slots. |
| </span>block: <span class="kw-2">*const </span>u8, |
| |
| <span class="doccomment">/// The offset into the block. |
| </span>offset: usize, |
| } |
| |
| <span class="kw">impl </span>Default <span class="kw">for </span>ListToken { |
| <span class="attribute">#[inline] |
| </span><span class="kw">fn </span>default() -> <span class="self">Self </span>{ |
| ListToken { |
| block: ptr::null(), |
| offset: <span class="number">0</span>, |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Unbounded channel implemented as a linked list. |
| /// |
| /// Each message sent into the channel is assigned a sequence number, i.e. an index. Indices are |
| /// represented as numbers of type `usize` and wrap on overflow. |
| /// |
| /// Consecutive messages are grouped into blocks in order to put less pressure on the allocator and |
| /// improve cache efficiency. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Channel<T> { |
| <span class="doccomment">/// The head of the channel. |
| </span>head: CachePadded<Position<T>>, |
| |
| <span class="doccomment">/// The tail of the channel. |
| </span>tail: CachePadded<Position<T>>, |
| |
| <span class="doccomment">/// Receivers waiting while the channel is empty and not disconnected. |
| </span>receivers: SyncWaker, |
| |
| <span class="doccomment">/// Indicates that dropping a `Channel<T>` may drop messages of type `T`. |
| </span>_marker: PhantomData<T>, |
| } |
| |
| <span class="kw">impl</span><T> Channel<T> { |
| <span class="doccomment">/// Creates a new unbounded channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new() -> <span class="self">Self </span>{ |
| Channel { |
| head: CachePadded::new(Position { |
| block: AtomicPtr::new(ptr::null_mut()), |
| index: AtomicUsize::new(<span class="number">0</span>), |
| }), |
| tail: CachePadded::new(Position { |
| block: AtomicPtr::new(ptr::null_mut()), |
| index: AtomicUsize::new(<span class="number">0</span>), |
| }), |
| receivers: SyncWaker::new(), |
| _marker: PhantomData, |
| } |
| } |
| |
| <span class="doccomment">/// Returns a receiver handle to the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>receiver(<span class="kw-2">&</span><span class="self">self</span>) -> Receiver<<span class="lifetime">'_</span>, T> { |
| Receiver(<span class="self">self</span>) |
| } |
| |
| <span class="doccomment">/// Returns a sender handle to the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>sender(<span class="kw-2">&</span><span class="self">self</span>) -> Sender<<span class="lifetime">'_</span>, T> { |
| Sender(<span class="self">self</span>) |
| } |
| |
| <span class="doccomment">/// Attempts to reserve a slot for sending a message. |
| </span><span class="kw">fn </span>start_send(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token) -> bool { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">let </span><span class="kw-2">mut </span>tail = <span class="self">self</span>.tail.index.load(Ordering::Acquire); |
| <span class="kw">let </span><span class="kw-2">mut </span>block = <span class="self">self</span>.tail.block.load(Ordering::Acquire); |
| <span class="kw">let </span><span class="kw-2">mut </span>next_block = <span class="prelude-val">None</span>; |
| |
| <span class="kw">loop </span>{ |
| <span class="comment">// Check if the channel is disconnected. |
| </span><span class="kw">if </span>tail & MARK_BIT != <span class="number">0 </span>{ |
| token.list.block = ptr::null(); |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } |
| |
| <span class="comment">// Calculate the offset of the index into the block. |
| </span><span class="kw">let </span>offset = (tail >> SHIFT) % LAP; |
| |
| <span class="comment">// If we reached the end of the block, wait until the next one is installed. |
| </span><span class="kw">if </span>offset == BLOCK_CAP { |
| backoff.snooze(); |
| tail = <span class="self">self</span>.tail.index.load(Ordering::Acquire); |
| block = <span class="self">self</span>.tail.block.load(Ordering::Acquire); |
| <span class="kw">continue</span>; |
| } |
| |
| <span class="comment">// If we're going to have to install the next block, allocate it in advance in order to |
| // make the wait for other threads as short as possible. |
| </span><span class="kw">if </span>offset + <span class="number">1 </span>== BLOCK_CAP && next_block.is_none() { |
| next_block = <span class="prelude-val">Some</span>(Box::new(Block::<T>::new())); |
| } |
| |
| <span class="comment">// If this is the first message to be sent into the channel, we need to allocate the |
| // first block and install it. |
| </span><span class="kw">if </span>block.is_null() { |
| <span class="kw">let </span>new = Box::into_raw(Box::new(Block::<T>::new())); |
| |
| <span class="kw">if </span><span class="self">self |
| </span>.tail |
| .block |
| .compare_exchange(block, new, Ordering::Release, Ordering::Relaxed) |
| .is_ok() |
| { |
| <span class="self">self</span>.head.block.store(new, Ordering::Release); |
| block = new; |
| } <span class="kw">else </span>{ |
| next_block = <span class="kw">unsafe </span>{ <span class="prelude-val">Some</span>(Box::from_raw(new)) }; |
| tail = <span class="self">self</span>.tail.index.load(Ordering::Acquire); |
| block = <span class="self">self</span>.tail.block.load(Ordering::Acquire); |
| <span class="kw">continue</span>; |
| } |
| } |
| |
| <span class="kw">let </span>new_tail = tail + (<span class="number">1 </span><< SHIFT); |
| |
| <span class="comment">// Try advancing the tail forward. |
| </span><span class="kw">match </span><span class="self">self</span>.tail.index.compare_exchange_weak( |
| tail, |
| new_tail, |
| Ordering::SeqCst, |
| Ordering::Acquire, |
| ) { |
| <span class="prelude-val">Ok</span>(<span class="kw">_</span>) => <span class="kw">unsafe </span>{ |
| <span class="comment">// If we've reached the end of the block, install the next one. |
| </span><span class="kw">if </span>offset + <span class="number">1 </span>== BLOCK_CAP { |
| <span class="kw">let </span>next_block = Box::into_raw(next_block.unwrap()); |
| <span class="self">self</span>.tail.block.store(next_block, Ordering::Release); |
| <span class="self">self</span>.tail.index.fetch_add(<span class="number">1 </span><< SHIFT, Ordering::Release); |
| (<span class="kw-2">*</span>block).next.store(next_block, Ordering::Release); |
| } |
| |
| token.list.block = block <span class="kw">as </span><span class="kw-2">*const </span>u8; |
| token.list.offset = offset; |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| }, |
| <span class="prelude-val">Err</span>(t) => { |
| tail = t; |
| block = <span class="self">self</span>.tail.block.load(Ordering::Acquire); |
| backoff.spin(); |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Writes a message into the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe fn </span>write(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token, msg: T) -> <span class="prelude-ty">Result</span><(), T> { |
| <span class="comment">// If there is no slot, the channel is disconnected. |
| </span><span class="kw">if </span>token.list.block.is_null() { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(msg); |
| } |
| |
| <span class="comment">// Write the message into the slot. |
| </span><span class="kw">let </span>block = token.list.block.cast::<Block<T>>(); |
| <span class="kw">let </span>offset = token.list.offset; |
| <span class="kw">let </span>slot = (<span class="kw-2">*</span>block).slots.get_unchecked(offset); |
| slot.msg.get().write(MaybeUninit::new(msg)); |
| slot.state.fetch_or(WRITE, Ordering::Release); |
| |
| <span class="comment">// Wake a sleeping receiver. |
| </span><span class="self">self</span>.receivers.notify(); |
| <span class="prelude-val">Ok</span>(()) |
| } |
| |
| <span class="doccomment">/// Attempts to reserve a slot for receiving a message. |
| </span><span class="kw">fn </span>start_recv(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token) -> bool { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">let </span><span class="kw-2">mut </span>head = <span class="self">self</span>.head.index.load(Ordering::Acquire); |
| <span class="kw">let </span><span class="kw-2">mut </span>block = <span class="self">self</span>.head.block.load(Ordering::Acquire); |
| |
| <span class="kw">loop </span>{ |
| <span class="comment">// Calculate the offset of the index into the block. |
| </span><span class="kw">let </span>offset = (head >> SHIFT) % LAP; |
| |
| <span class="comment">// If we reached the end of the block, wait until the next one is installed. |
| </span><span class="kw">if </span>offset == BLOCK_CAP { |
| backoff.snooze(); |
| head = <span class="self">self</span>.head.index.load(Ordering::Acquire); |
| block = <span class="self">self</span>.head.block.load(Ordering::Acquire); |
| <span class="kw">continue</span>; |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>new_head = head + (<span class="number">1 </span><< SHIFT); |
| |
| <span class="kw">if </span>new_head & MARK_BIT == <span class="number">0 </span>{ |
| atomic::fence(Ordering::SeqCst); |
| <span class="kw">let </span>tail = <span class="self">self</span>.tail.index.load(Ordering::Relaxed); |
| |
| <span class="comment">// If the tail equals the head, that means the channel is empty. |
| </span><span class="kw">if </span>head >> SHIFT == tail >> SHIFT { |
| <span class="comment">// If the channel is disconnected... |
| </span><span class="kw">if </span>tail & MARK_BIT != <span class="number">0 </span>{ |
| <span class="comment">// ...then receive an error. |
| </span>token.list.block = ptr::null(); |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } <span class="kw">else </span>{ |
| <span class="comment">// Otherwise, the receive operation is not ready. |
| </span><span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| } |
| |
| <span class="comment">// If head and tail are not in the same block, set `MARK_BIT` in head. |
| </span><span class="kw">if </span>(head >> SHIFT) / LAP != (tail >> SHIFT) / LAP { |
| new_head |= MARK_BIT; |
| } |
| } |
| |
| <span class="comment">// The block can be null here only if the first message is being sent into the channel. |
| // In that case, just wait until it gets initialized. |
| </span><span class="kw">if </span>block.is_null() { |
| backoff.snooze(); |
| head = <span class="self">self</span>.head.index.load(Ordering::Acquire); |
| block = <span class="self">self</span>.head.block.load(Ordering::Acquire); |
| <span class="kw">continue</span>; |
| } |
| |
| <span class="comment">// Try moving the head index forward. |
| </span><span class="kw">match </span><span class="self">self</span>.head.index.compare_exchange_weak( |
| head, |
| new_head, |
| Ordering::SeqCst, |
| Ordering::Acquire, |
| ) { |
| <span class="prelude-val">Ok</span>(<span class="kw">_</span>) => <span class="kw">unsafe </span>{ |
| <span class="comment">// If we've reached the end of the block, move to the next one. |
| </span><span class="kw">if </span>offset + <span class="number">1 </span>== BLOCK_CAP { |
| <span class="kw">let </span>next = (<span class="kw-2">*</span>block).wait_next(); |
| <span class="kw">let </span><span class="kw-2">mut </span>next_index = (new_head & !MARK_BIT).wrapping_add(<span class="number">1 </span><< SHIFT); |
| <span class="kw">if </span>!(<span class="kw-2">*</span>next).next.load(Ordering::Relaxed).is_null() { |
| next_index |= MARK_BIT; |
| } |
| |
| <span class="self">self</span>.head.block.store(next, Ordering::Release); |
| <span class="self">self</span>.head.index.store(next_index, Ordering::Release); |
| } |
| |
| token.list.block = block <span class="kw">as </span><span class="kw-2">*const </span>u8; |
| token.list.offset = offset; |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| }, |
| <span class="prelude-val">Err</span>(h) => { |
| head = h; |
| block = <span class="self">self</span>.head.block.load(Ordering::Acquire); |
| backoff.spin(); |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Reads a message from the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe fn </span>read(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token) -> <span class="prelude-ty">Result</span><T, ()> { |
| <span class="kw">if </span>token.list.block.is_null() { |
| <span class="comment">// The channel is disconnected. |
| </span><span class="kw">return </span><span class="prelude-val">Err</span>(()); |
| } |
| |
| <span class="comment">// Read the message. |
| </span><span class="kw">let </span>block = token.list.block <span class="kw">as </span><span class="kw-2">*mut </span>Block<T>; |
| <span class="kw">let </span>offset = token.list.offset; |
| <span class="kw">let </span>slot = (<span class="kw-2">*</span>block).slots.get_unchecked(offset); |
| slot.wait_write(); |
| <span class="kw">let </span>msg = slot.msg.get().read().assume_init(); |
| |
| <span class="comment">// Destroy the block if we've reached the end, or if another thread wanted to destroy but |
| // couldn't because we were busy reading from the slot. |
| </span><span class="kw">if </span>offset + <span class="number">1 </span>== BLOCK_CAP { |
| Block::destroy(block, <span class="number">0</span>); |
| } <span class="kw">else if </span>slot.state.fetch_or(READ, Ordering::AcqRel) & DESTROY != <span class="number">0 </span>{ |
| Block::destroy(block, offset + <span class="number">1</span>); |
| } |
| |
| <span class="prelude-val">Ok</span>(msg) |
| } |
| |
| <span class="doccomment">/// Attempts to send a message into the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>try_send(<span class="kw-2">&</span><span class="self">self</span>, msg: T) -> <span class="prelude-ty">Result</span><(), TrySendError<T>> { |
| <span class="self">self</span>.send(msg, <span class="prelude-val">None</span>).map_err(|err| <span class="kw">match </span>err { |
| SendTimeoutError::Disconnected(msg) => TrySendError::Disconnected(msg), |
| SendTimeoutError::Timeout(<span class="kw">_</span>) => <span class="macro">unreachable!</span>(), |
| }) |
| } |
| |
| <span class="doccomment">/// Sends a message into the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>send( |
| <span class="kw-2">&</span><span class="self">self</span>, |
| msg: T, |
| _deadline: <span class="prelude-ty">Option</span><Instant>, |
| ) -> <span class="prelude-ty">Result</span><(), SendTimeoutError<T>> { |
| <span class="kw">let </span>token = <span class="kw-2">&mut </span>Token::default(); |
| <span class="macro">assert!</span>(<span class="self">self</span>.start_send(token)); |
| <span class="kw">unsafe </span>{ |
| <span class="self">self</span>.write(token, msg) |
| .map_err(SendTimeoutError::Disconnected) |
| } |
| } |
| |
| <span class="doccomment">/// Attempts to receive a message without blocking. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>try_recv(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Result</span><T, TryRecvError> { |
| <span class="kw">let </span>token = <span class="kw-2">&mut </span>Token::default(); |
| |
| <span class="kw">if </span><span class="self">self</span>.start_recv(token) { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.read(token).map_err(|<span class="kw">_</span>| TryRecvError::Disconnected) } |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Err</span>(TryRecvError::Empty) |
| } |
| } |
| |
| <span class="doccomment">/// Receives a message from the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>recv(<span class="kw-2">&</span><span class="self">self</span>, deadline: <span class="prelude-ty">Option</span><Instant>) -> <span class="prelude-ty">Result</span><T, RecvTimeoutError> { |
| <span class="kw">let </span>token = <span class="kw-2">&mut </span>Token::default(); |
| <span class="kw">loop </span>{ |
| <span class="comment">// Try receiving a message several times. |
| </span><span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">loop </span>{ |
| <span class="kw">if </span><span class="self">self</span>.start_recv(token) { |
| <span class="kw">unsafe </span>{ |
| <span class="kw">return </span><span class="self">self</span>.read(token).map_err(|<span class="kw">_</span>| RecvTimeoutError::Disconnected); |
| } |
| } |
| |
| <span class="kw">if </span>backoff.is_completed() { |
| <span class="kw">break</span>; |
| } <span class="kw">else </span>{ |
| backoff.snooze(); |
| } |
| } |
| |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(d) = deadline { |
| <span class="kw">if </span>Instant::now() >= d { |
| <span class="kw">return </span><span class="prelude-val">Err</span>(RecvTimeoutError::Timeout); |
| } |
| } |
| |
| <span class="comment">// Prepare for blocking until a sender wakes us up. |
| </span>Context::with(|cx| { |
| <span class="kw">let </span>oper = Operation::hook(token); |
| <span class="self">self</span>.receivers.register(oper, cx); |
| |
| <span class="comment">// Has the channel become ready just now? |
| </span><span class="kw">if </span>!<span class="self">self</span>.is_empty() || <span class="self">self</span>.is_disconnected() { |
| <span class="kw">let _ </span>= cx.try_select(Selected::Aborted); |
| } |
| |
| <span class="comment">// Block the current thread. |
| </span><span class="kw">let </span>sel = cx.wait_until(deadline); |
| |
| <span class="kw">match </span>sel { |
| Selected::Waiting => <span class="macro">unreachable!</span>(), |
| Selected::Aborted | Selected::Disconnected => { |
| <span class="self">self</span>.receivers.unregister(oper).unwrap(); |
| <span class="comment">// If the channel was disconnected, we still have to check for remaining |
| // messages. |
| </span>} |
| Selected::Operation(<span class="kw">_</span>) => {} |
| } |
| }); |
| } |
| } |
| |
| <span class="doccomment">/// Returns the current number of messages inside the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>len(<span class="kw-2">&</span><span class="self">self</span>) -> usize { |
| <span class="kw">loop </span>{ |
| <span class="comment">// Load the tail index, then load the head index. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>tail = <span class="self">self</span>.tail.index.load(Ordering::SeqCst); |
| <span class="kw">let </span><span class="kw-2">mut </span>head = <span class="self">self</span>.head.index.load(Ordering::SeqCst); |
| |
| <span class="comment">// If the tail index didn't change, we've got consistent indices to work with. |
| </span><span class="kw">if </span><span class="self">self</span>.tail.index.load(Ordering::SeqCst) == tail { |
| <span class="comment">// Erase the lower bits. |
| </span>tail &= !((<span class="number">1 </span><< SHIFT) - <span class="number">1</span>); |
| head &= !((<span class="number">1 </span><< SHIFT) - <span class="number">1</span>); |
| |
| <span class="comment">// Fix up indices if they fall onto block ends. |
| </span><span class="kw">if </span>(tail >> SHIFT) & (LAP - <span class="number">1</span>) == LAP - <span class="number">1 </span>{ |
| tail = tail.wrapping_add(<span class="number">1 </span><< SHIFT); |
| } |
| <span class="kw">if </span>(head >> SHIFT) & (LAP - <span class="number">1</span>) == LAP - <span class="number">1 </span>{ |
| head = head.wrapping_add(<span class="number">1 </span><< SHIFT); |
| } |
| |
| <span class="comment">// Rotate indices so that head falls into the first block. |
| </span><span class="kw">let </span>lap = (head >> SHIFT) / LAP; |
| tail = tail.wrapping_sub((lap * LAP) << SHIFT); |
| head = head.wrapping_sub((lap * LAP) << SHIFT); |
| |
| <span class="comment">// Remove the lower bits. |
| </span>tail >>= SHIFT; |
| head >>= SHIFT; |
| |
| <span class="comment">// Return the difference minus the number of blocks between tail and head. |
| </span><span class="kw">return </span>tail - head - tail / LAP; |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Returns the capacity of the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>capacity(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><usize> { |
| <span class="prelude-val">None |
| </span>} |
| |
| <span class="doccomment">/// Disconnects senders and wakes up all blocked receivers. |
| /// |
| /// Returns `true` if this call disconnected the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>disconnect_senders(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">let </span>tail = <span class="self">self</span>.tail.index.fetch_or(MARK_BIT, Ordering::SeqCst); |
| |
| <span class="kw">if </span>tail & MARK_BIT == <span class="number">0 </span>{ |
| <span class="self">self</span>.receivers.disconnect(); |
| <span class="bool-val">true |
| </span>} <span class="kw">else </span>{ |
| <span class="bool-val">false |
| </span>} |
| } |
| |
| <span class="doccomment">/// Disconnects receivers. |
| /// |
| /// Returns `true` if this call disconnected the channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>disconnect_receivers(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">let </span>tail = <span class="self">self</span>.tail.index.fetch_or(MARK_BIT, Ordering::SeqCst); |
| |
| <span class="kw">if </span>tail & MARK_BIT == <span class="number">0 </span>{ |
| <span class="comment">// If receivers are dropped first, discard all messages to free |
| // memory eagerly. |
| </span><span class="self">self</span>.discard_all_messages(); |
| <span class="bool-val">true |
| </span>} <span class="kw">else </span>{ |
| <span class="bool-val">false |
| </span>} |
| } |
| |
| <span class="doccomment">/// Discards all messages. |
| /// |
| /// This method should only be called when all receivers are dropped. |
| </span><span class="kw">fn </span>discard_all_messages(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="kw">let </span>backoff = Backoff::new(); |
| <span class="kw">let </span><span class="kw-2">mut </span>tail = <span class="self">self</span>.tail.index.load(Ordering::Acquire); |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>offset = (tail >> SHIFT) % LAP; |
| <span class="kw">if </span>offset != BLOCK_CAP { |
| <span class="kw">break</span>; |
| } |
| |
| <span class="comment">// New updates to tail will be rejected by MARK_BIT and aborted unless it's |
| // at boundary. We need to wait for the updates take affect otherwise there |
| // can be memory leaks. |
| </span>backoff.snooze(); |
| tail = <span class="self">self</span>.tail.index.load(Ordering::Acquire); |
| } |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>head = <span class="self">self</span>.head.index.load(Ordering::Acquire); |
| <span class="kw">let </span><span class="kw-2">mut </span>block = <span class="self">self</span>.head.block.load(Ordering::Acquire); |
| |
| <span class="comment">// If we're going to be dropping messages we need to synchronize with initialization |
| </span><span class="kw">if </span>head >> SHIFT != tail >> SHIFT { |
| <span class="comment">// The block can be null here only if a sender is in the process of initializing the |
| // channel while another sender managed to send a message by inserting it into the |
| // semi-initialized channel and advanced the tail. |
| // In that case, just wait until it gets initialized. |
| </span><span class="kw">while </span>block.is_null() { |
| backoff.snooze(); |
| block = <span class="self">self</span>.head.block.load(Ordering::Acquire); |
| } |
| } |
| <span class="kw">unsafe </span>{ |
| <span class="comment">// Drop all messages between head and tail and deallocate the heap-allocated blocks. |
| </span><span class="kw">while </span>head >> SHIFT != tail >> SHIFT { |
| <span class="kw">let </span>offset = (head >> SHIFT) % LAP; |
| |
| <span class="kw">if </span>offset < BLOCK_CAP { |
| <span class="comment">// Drop the message in the slot. |
| </span><span class="kw">let </span>slot = (<span class="kw-2">*</span>block).slots.get_unchecked(offset); |
| slot.wait_write(); |
| <span class="kw">let </span>p = <span class="kw-2">&mut *</span>slot.msg.get(); |
| p.as_mut_ptr().drop_in_place(); |
| } <span class="kw">else </span>{ |
| (<span class="kw-2">*</span>block).wait_next(); |
| <span class="comment">// Deallocate the block and move to the next one. |
| </span><span class="kw">let </span>next = (<span class="kw-2">*</span>block).next.load(Ordering::Acquire); |
| drop(Box::from_raw(block)); |
| block = next; |
| } |
| |
| head = head.wrapping_add(<span class="number">1 </span><< SHIFT); |
| } |
| |
| <span class="comment">// Deallocate the last remaining block. |
| </span><span class="kw">if </span>!block.is_null() { |
| drop(Box::from_raw(block)); |
| } |
| } |
| head &= !MARK_BIT; |
| <span class="self">self</span>.head.block.store(ptr::null_mut(), Ordering::Release); |
| <span class="self">self</span>.head.index.store(head, Ordering::Release); |
| } |
| |
| <span class="doccomment">/// Returns `true` if the channel is disconnected. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>is_disconnected(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="self">self</span>.tail.index.load(Ordering::SeqCst) & MARK_BIT != <span class="number">0 |
| </span>} |
| |
| <span class="doccomment">/// Returns `true` if the channel is empty. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>is_empty(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">let </span>head = <span class="self">self</span>.head.index.load(Ordering::SeqCst); |
| <span class="kw">let </span>tail = <span class="self">self</span>.tail.index.load(Ordering::SeqCst); |
| head >> SHIFT == tail >> SHIFT |
| } |
| |
| <span class="doccomment">/// Returns `true` if the channel is full. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>is_full(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="bool-val">false |
| </span>} |
| } |
| |
| <span class="kw">impl</span><T> Drop <span class="kw">for </span>Channel<T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">let </span><span class="kw-2">mut </span>head = <span class="kw-2">*</span><span class="self">self</span>.head.index.get_mut(); |
| <span class="kw">let </span><span class="kw-2">mut </span>tail = <span class="kw-2">*</span><span class="self">self</span>.tail.index.get_mut(); |
| <span class="kw">let </span><span class="kw-2">mut </span>block = <span class="kw-2">*</span><span class="self">self</span>.head.block.get_mut(); |
| |
| <span class="comment">// Erase the lower bits. |
| </span>head &= !((<span class="number">1 </span><< SHIFT) - <span class="number">1</span>); |
| tail &= !((<span class="number">1 </span><< SHIFT) - <span class="number">1</span>); |
| |
| <span class="kw">unsafe </span>{ |
| <span class="comment">// Drop all messages between head and tail and deallocate the heap-allocated blocks. |
| </span><span class="kw">while </span>head != tail { |
| <span class="kw">let </span>offset = (head >> SHIFT) % LAP; |
| |
| <span class="kw">if </span>offset < BLOCK_CAP { |
| <span class="comment">// Drop the message in the slot. |
| </span><span class="kw">let </span>slot = (<span class="kw-2">*</span>block).slots.get_unchecked(offset); |
| <span class="kw">let </span>p = <span class="kw-2">&mut *</span>slot.msg.get(); |
| p.as_mut_ptr().drop_in_place(); |
| } <span class="kw">else </span>{ |
| <span class="comment">// Deallocate the block and move to the next one. |
| </span><span class="kw">let </span>next = <span class="kw-2">*</span>(<span class="kw-2">*</span>block).next.get_mut(); |
| drop(Box::from_raw(block)); |
| block = next; |
| } |
| |
| head = head.wrapping_add(<span class="number">1 </span><< SHIFT); |
| } |
| |
| <span class="comment">// Deallocate the last remaining block. |
| </span><span class="kw">if </span>!block.is_null() { |
| drop(Box::from_raw(block)); |
| } |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Receiver handle to a channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Receiver<<span class="lifetime">'a</span>, T>(<span class="kw-2">&</span><span class="lifetime">'a </span>Channel<T>); |
| |
| <span class="doccomment">/// Sender handle to a channel. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Sender<<span class="lifetime">'a</span>, T>(<span class="kw-2">&</span><span class="lifetime">'a </span>Channel<T>); |
| |
| <span class="kw">impl</span><T> SelectHandle <span class="kw">for </span>Receiver<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>try_select(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token) -> bool { |
| <span class="self">self</span>.<span class="number">0</span>.start_recv(token) |
| } |
| |
| <span class="kw">fn </span>deadline(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><Instant> { |
| <span class="prelude-val">None |
| </span>} |
| |
| <span class="kw">fn </span>register(<span class="kw-2">&</span><span class="self">self</span>, oper: Operation, cx: <span class="kw-2">&</span>Context) -> bool { |
| <span class="self">self</span>.<span class="number">0</span>.receivers.register(oper, cx); |
| <span class="self">self</span>.is_ready() |
| } |
| |
| <span class="kw">fn </span>unregister(<span class="kw-2">&</span><span class="self">self</span>, oper: Operation) { |
| <span class="self">self</span>.<span class="number">0</span>.receivers.unregister(oper); |
| } |
| |
| <span class="kw">fn </span>accept(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token, _cx: <span class="kw-2">&</span>Context) -> bool { |
| <span class="self">self</span>.try_select(token) |
| } |
| |
| <span class="kw">fn </span>is_ready(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| !<span class="self">self</span>.<span class="number">0</span>.is_empty() || <span class="self">self</span>.<span class="number">0</span>.is_disconnected() |
| } |
| |
| <span class="kw">fn </span>watch(<span class="kw-2">&</span><span class="self">self</span>, oper: Operation, cx: <span class="kw-2">&</span>Context) -> bool { |
| <span class="self">self</span>.<span class="number">0</span>.receivers.watch(oper, cx); |
| <span class="self">self</span>.is_ready() |
| } |
| |
| <span class="kw">fn </span>unwatch(<span class="kw-2">&</span><span class="self">self</span>, oper: Operation) { |
| <span class="self">self</span>.<span class="number">0</span>.receivers.unwatch(oper); |
| } |
| } |
| |
| <span class="kw">impl</span><T> SelectHandle <span class="kw">for </span>Sender<<span class="lifetime">'_</span>, T> { |
| <span class="kw">fn </span>try_select(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token) -> bool { |
| <span class="self">self</span>.<span class="number">0</span>.start_send(token) |
| } |
| |
| <span class="kw">fn </span>deadline(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><Instant> { |
| <span class="prelude-val">None |
| </span>} |
| |
| <span class="kw">fn </span>register(<span class="kw-2">&</span><span class="self">self</span>, _oper: Operation, _cx: <span class="kw-2">&</span>Context) -> bool { |
| <span class="self">self</span>.is_ready() |
| } |
| |
| <span class="kw">fn </span>unregister(<span class="kw-2">&</span><span class="self">self</span>, _oper: Operation) {} |
| |
| <span class="kw">fn </span>accept(<span class="kw-2">&</span><span class="self">self</span>, token: <span class="kw-2">&mut </span>Token, _cx: <span class="kw-2">&</span>Context) -> bool { |
| <span class="self">self</span>.try_select(token) |
| } |
| |
| <span class="kw">fn </span>is_ready(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="bool-val">true |
| </span>} |
| |
| <span class="kw">fn </span>watch(<span class="kw-2">&</span><span class="self">self</span>, _oper: Operation, _cx: <span class="kw-2">&</span>Context) -> bool { |
| <span class="self">self</span>.is_ready() |
| } |
| |
| <span class="kw">fn </span>unwatch(<span class="kw-2">&</span><span class="self">self</span>, _oper: Operation) {} |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="crossbeam_channel" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
