| <!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/git/checkouts/tokio-377c595163f99a10/dfe252d/tokio/src/runtime/scheduler/multi_thread/idle.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>idle.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="doccomment">//! Coordinates idling workers |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::loom::sync::atomic::AtomicUsize; |
| <span class="kw">use </span><span class="kw">crate</span>::loom::sync::Mutex; |
| |
| <span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::sync::atomic::Ordering::{<span class="self">self</span>, SeqCst}; |
| |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Idle { |
| <span class="doccomment">/// Tracks both the number of searching workers and the number of unparked |
| /// workers. |
| /// |
| /// Used as a fast-path to avoid acquiring the lock when needed. |
| </span>state: AtomicUsize, |
| |
| <span class="doccomment">/// Sleeping workers |
| </span>sleepers: Mutex<Vec<usize>>, |
| |
| <span class="doccomment">/// Total number of workers. |
| </span>num_workers: usize, |
| } |
| |
| <span class="kw">const </span>UNPARK_SHIFT: usize = <span class="number">16</span>; |
| <span class="kw">const </span>UNPARK_MASK: usize = !SEARCH_MASK; |
| <span class="kw">const </span>SEARCH_MASK: usize = (<span class="number">1 </span><< UNPARK_SHIFT) - <span class="number">1</span>; |
| |
| <span class="attribute">#[derive(Copy, Clone)] |
| </span><span class="kw">struct </span>State(usize); |
| |
| <span class="kw">impl </span>Idle { |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>new(num_workers: usize) -> Idle { |
| <span class="kw">let </span>init = State::new(num_workers); |
| |
| Idle { |
| state: AtomicUsize::new(init.into()), |
| sleepers: Mutex::new(Vec::with_capacity(num_workers)), |
| num_workers, |
| } |
| } |
| |
| <span class="doccomment">/// If there are no workers actively searching, returns the index of a |
| /// worker currently sleeping. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>worker_to_notify(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><usize> { |
| <span class="comment">// If at least one worker is spinning, work being notified will |
| // eventually be found. A searching thread will find **some** work and |
| // notify another worker, eventually leading to our work being found. |
| // |
| // For this to happen, this load must happen before the thread |
| // transitioning `num_searching` to zero. Acquire / Release does not |
| // provide sufficient guarantees, so this load is done with `SeqCst` and |
| // will pair with the `fetch_sub(1)` when transitioning out of |
| // searching. |
| </span><span class="kw">if </span>!<span class="self">self</span>.notify_should_wakeup() { |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| |
| <span class="comment">// Acquire the lock |
| </span><span class="kw">let </span><span class="kw-2">mut </span>sleepers = <span class="self">self</span>.sleepers.lock(); |
| |
| <span class="comment">// Check again, now that the lock is acquired |
| </span><span class="kw">if </span>!<span class="self">self</span>.notify_should_wakeup() { |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| |
| <span class="comment">// A worker should be woken up, atomically increment the number of |
| // searching workers as well as the number of unparked workers. |
| </span>State::unpark_one(<span class="kw-2">&</span><span class="self">self</span>.state, <span class="number">1</span>); |
| |
| <span class="comment">// Get the worker to unpark |
| </span><span class="kw">let </span>ret = sleepers.pop(); |
| <span class="macro">debug_assert!</span>(ret.is_some()); |
| |
| ret |
| } |
| |
| <span class="doccomment">/// Returns `true` if the worker needs to do a final check for submitted |
| /// work. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>transition_worker_to_parked(<span class="kw-2">&</span><span class="self">self</span>, worker: usize, is_searching: bool) -> bool { |
| <span class="comment">// Acquire the lock |
| </span><span class="kw">let </span><span class="kw-2">mut </span>sleepers = <span class="self">self</span>.sleepers.lock(); |
| |
| <span class="comment">// Decrement the number of unparked threads |
| </span><span class="kw">let </span>ret = State::dec_num_unparked(<span class="kw-2">&</span><span class="self">self</span>.state, is_searching); |
| |
| <span class="comment">// Track the sleeping worker |
| </span>sleepers.push(worker); |
| |
| ret |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>transition_worker_to_searching(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">let </span>state = State::load(<span class="kw-2">&</span><span class="self">self</span>.state, SeqCst); |
| <span class="kw">if </span><span class="number">2 </span>* state.num_searching() >= <span class="self">self</span>.num_workers { |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| |
| <span class="comment">// It is possible for this routine to allow more than 50% of the workers |
| // to search. That is OK. Limiting searchers is only an optimization to |
| // prevent too much contention. |
| </span>State::inc_num_searching(<span class="kw-2">&</span><span class="self">self</span>.state, SeqCst); |
| <span class="bool-val">true |
| </span>} |
| |
| <span class="doccomment">/// A lightweight transition from searching -> running. |
| /// |
| /// Returns `true` if this is the final searching worker. The caller |
| /// **must** notify a new worker. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>transition_worker_from_searching(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| State::dec_num_searching(<span class="kw-2">&</span><span class="self">self</span>.state) |
| } |
| |
| <span class="doccomment">/// Unpark a specific worker. This happens if tasks are submitted from |
| /// within the worker's park routine. |
| /// |
| /// Returns `true` if the worker was parked before calling the method. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>unpark_worker_by_id(<span class="kw-2">&</span><span class="self">self</span>, worker_id: usize) -> bool { |
| <span class="kw">let </span><span class="kw-2">mut </span>sleepers = <span class="self">self</span>.sleepers.lock(); |
| |
| <span class="kw">for </span>index <span class="kw">in </span><span class="number">0</span>..sleepers.len() { |
| <span class="kw">if </span>sleepers[index] == worker_id { |
| sleepers.swap_remove(index); |
| |
| <span class="comment">// Update the state accordingly while the lock is held. |
| </span>State::unpark_one(<span class="kw-2">&</span><span class="self">self</span>.state, <span class="number">0</span>); |
| |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } |
| } |
| |
| <span class="bool-val">false |
| </span>} |
| |
| <span class="doccomment">/// Returns `true` if `worker_id` is contained in the sleep set. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>is_parked(<span class="kw-2">&</span><span class="self">self</span>, worker_id: usize) -> bool { |
| <span class="kw">let </span>sleepers = <span class="self">self</span>.sleepers.lock(); |
| sleepers.contains(<span class="kw-2">&</span>worker_id) |
| } |
| |
| <span class="kw">fn </span>notify_should_wakeup(<span class="kw-2">&</span><span class="self">self</span>) -> bool { |
| <span class="kw">let </span>state = State(<span class="self">self</span>.state.fetch_add(<span class="number">0</span>, SeqCst)); |
| state.num_searching() == <span class="number">0 </span>&& state.num_unparked() < <span class="self">self</span>.num_workers |
| } |
| } |
| |
| <span class="kw">impl </span>State { |
| <span class="kw">fn </span>new(num_workers: usize) -> State { |
| <span class="comment">// All workers start in the unparked state |
| </span><span class="kw">let </span>ret = State(num_workers << UNPARK_SHIFT); |
| <span class="macro">debug_assert_eq!</span>(num_workers, ret.num_unparked()); |
| <span class="macro">debug_assert_eq!</span>(<span class="number">0</span>, ret.num_searching()); |
| ret |
| } |
| |
| <span class="kw">fn </span>load(cell: <span class="kw-2">&</span>AtomicUsize, ordering: Ordering) -> State { |
| State(cell.load(ordering)) |
| } |
| |
| <span class="kw">fn </span>unpark_one(cell: <span class="kw-2">&</span>AtomicUsize, num_searching: usize) { |
| cell.fetch_add(num_searching | (<span class="number">1 </span><< UNPARK_SHIFT), SeqCst); |
| } |
| |
| <span class="kw">fn </span>inc_num_searching(cell: <span class="kw-2">&</span>AtomicUsize, ordering: Ordering) { |
| cell.fetch_add(<span class="number">1</span>, ordering); |
| } |
| |
| <span class="doccomment">/// Returns `true` if this is the final searching worker |
| </span><span class="kw">fn </span>dec_num_searching(cell: <span class="kw-2">&</span>AtomicUsize) -> bool { |
| <span class="kw">let </span>state = State(cell.fetch_sub(<span class="number">1</span>, SeqCst)); |
| state.num_searching() == <span class="number">1 |
| </span>} |
| |
| <span class="doccomment">/// Track a sleeping worker |
| /// |
| /// Returns `true` if this is the final searching worker. |
| </span><span class="kw">fn </span>dec_num_unparked(cell: <span class="kw-2">&</span>AtomicUsize, is_searching: bool) -> bool { |
| <span class="kw">let </span><span class="kw-2">mut </span>dec = <span class="number">1 </span><< UNPARK_SHIFT; |
| |
| <span class="kw">if </span>is_searching { |
| dec += <span class="number">1</span>; |
| } |
| |
| <span class="kw">let </span>prev = State(cell.fetch_sub(dec, SeqCst)); |
| is_searching && prev.num_searching() == <span class="number">1 |
| </span>} |
| |
| <span class="doccomment">/// Number of workers currently searching |
| </span><span class="kw">fn </span>num_searching(<span class="self">self</span>) -> usize { |
| <span class="self">self</span>.<span class="number">0 </span>& SEARCH_MASK |
| } |
| |
| <span class="doccomment">/// Number of workers currently unparked |
| </span><span class="kw">fn </span>num_unparked(<span class="self">self</span>) -> usize { |
| (<span class="self">self</span>.<span class="number">0 </span>& UNPARK_MASK) >> UNPARK_SHIFT |
| } |
| } |
| |
| <span class="kw">impl </span>From<usize> <span class="kw">for </span>State { |
| <span class="kw">fn </span>from(src: usize) -> State { |
| State(src) |
| } |
| } |
| |
| <span class="kw">impl </span>From<State> <span class="kw">for </span>usize { |
| <span class="kw">fn </span>from(src: State) -> usize { |
| src.<span class="number">0 |
| </span>} |
| } |
| |
| <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>State { |
| <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">"worker::State"</span>) |
| .field(<span class="string">"num_unparked"</span>, <span class="kw-2">&</span><span class="self">self</span>.num_unparked()) |
| .field(<span class="string">"num_searching"</span>, <span class="kw-2">&</span><span class="self">self</span>.num_searching()) |
| .finish() |
| } |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_state() { |
| <span class="macro">assert_eq!</span>(<span class="number">0</span>, UNPARK_MASK & SEARCH_MASK); |
| <span class="macro">assert_eq!</span>(<span class="number">0</span>, !(UNPARK_MASK | SEARCH_MASK)); |
| |
| <span class="kw">let </span>state = State::new(<span class="number">10</span>); |
| <span class="macro">assert_eq!</span>(<span class="number">10</span>, state.num_unparked()); |
| <span class="macro">assert_eq!</span>(<span class="number">0</span>, state.num_searching()); |
| } |
| </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> |
