| <!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/time/wheel/level.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>level.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 </span><span class="kw">crate</span>::runtime::time::{EntryList, TimerHandle, TimerShared}; |
| |
| <span class="kw">use </span>std::{fmt, ptr::NonNull}; |
| |
| <span class="doccomment">/// Wheel for a single level in the timer. This wheel contains 64 slots. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Level { |
| level: usize, |
| |
| <span class="doccomment">/// Bit field tracking which slots currently contain entries. |
| /// |
| /// Using a bit field to track slots that contain entries allows avoiding a |
| /// scan to find entries. This field is updated when entries are added or |
| /// removed from a slot. |
| /// |
| /// The least-significant bit represents slot zero. |
| </span>occupied: u64, |
| |
| <span class="doccomment">/// Slots. We access these via the EntryInner `current_list` as well, so this needs to be an UnsafeCell. |
| </span>slot: [EntryList; LEVEL_MULT], |
| } |
| |
| <span class="doccomment">/// Indicates when a slot must be processed next. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Expiration { |
| <span class="doccomment">/// The level containing the slot. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) level: usize, |
| |
| <span class="doccomment">/// The slot index. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) slot: usize, |
| |
| <span class="doccomment">/// The instant at which the slot needs to be processed. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) deadline: u64, |
| } |
| |
| <span class="doccomment">/// Level multiplier. |
| /// |
| /// Being a power of 2 is very important. |
| </span><span class="kw">const </span>LEVEL_MULT: usize = <span class="number">64</span>; |
| |
| <span class="kw">impl </span>Level { |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new(level: usize) -> Level { |
| <span class="comment">// A value has to be Copy in order to use syntax like: |
| // let stack = Stack::default(); |
| // ... |
| // slots: [stack; 64], |
| // |
| // Alternatively, since Stack is Default one can |
| // use syntax like: |
| // let slots: [Stack; 64] = Default::default(); |
| // |
| // However, that is only supported for arrays of size |
| // 32 or fewer. So in our case we have to explicitly |
| // invoke the constructor for each array element. |
| </span><span class="kw">let </span>ctor = EntryList::default; |
| |
| Level { |
| level, |
| occupied: <span class="number">0</span>, |
| slot: [ |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ctor(), |
| ], |
| } |
| } |
| |
| <span class="doccomment">/// Finds the slot that needs to be processed next and returns the slot and |
| /// `Instant` at which this slot must be processed. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>next_expiration(<span class="kw-2">&</span><span class="self">self</span>, now: u64) -> <span class="prelude-ty">Option</span><Expiration> { |
| <span class="comment">// Use the `occupied` bit field to get the index of the next slot that |
| // needs to be processed. |
| </span><span class="kw">let </span>slot = <span class="kw">match </span><span class="self">self</span>.next_occupied_slot(now) { |
| <span class="prelude-val">Some</span>(slot) => slot, |
| <span class="prelude-val">None </span>=> <span class="kw">return </span><span class="prelude-val">None</span>, |
| }; |
| |
| <span class="comment">// From the slot index, calculate the `Instant` at which it needs to be |
| // processed. This value *must* be in the future with respect to `now`. |
| |
| </span><span class="kw">let </span>level_range = level_range(<span class="self">self</span>.level); |
| <span class="kw">let </span>slot_range = slot_range(<span class="self">self</span>.level); |
| |
| <span class="comment">// Compute the start date of the current level by masking the low bits |
| // of `now` (`level_range` is a power of 2). |
| </span><span class="kw">let </span>level_start = now & !(level_range - <span class="number">1</span>); |
| <span class="kw">let </span><span class="kw-2">mut </span>deadline = level_start + slot <span class="kw">as </span>u64 * slot_range; |
| |
| <span class="kw">if </span>deadline <= now { |
| <span class="comment">// A timer is in a slot "prior" to the current time. This can occur |
| // because we do not have an infinite hierarchy of timer levels, and |
| // eventually a timer scheduled for a very distant time might end up |
| // being placed in a slot that is beyond the end of all of the |
| // arrays. |
| // |
| // To deal with this, we first limit timers to being scheduled no |
| // more than MAX_DURATION ticks in the future; that is, they're at |
| // most one rotation of the top level away. Then, we force timers |
| // that logically would go into the top+1 level, to instead go into |
| // the top level's slots. |
| // |
| // What this means is that the top level's slots act as a |
| // pseudo-ring buffer, and we rotate around them indefinitely. If we |
| // compute a deadline before now, and it's the top level, it |
| // therefore means we're actually looking at a slot in the future. |
| </span><span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.level, <span class="kw">super</span>::NUM_LEVELS - <span class="number">1</span>); |
| |
| deadline += level_range; |
| } |
| |
| <span class="macro">debug_assert!</span>( |
| deadline >= now, |
| <span class="string">"deadline={:016X}; now={:016X}; level={}; lr={:016X}, sr={:016X}, slot={}; occupied={:b}"</span>, |
| deadline, |
| now, |
| <span class="self">self</span>.level, |
| level_range, |
| slot_range, |
| slot, |
| <span class="self">self</span>.occupied |
| ); |
| |
| <span class="prelude-val">Some</span>(Expiration { |
| level: <span class="self">self</span>.level, |
| slot, |
| deadline, |
| }) |
| } |
| |
| <span class="kw">fn </span>next_occupied_slot(<span class="kw-2">&</span><span class="self">self</span>, now: u64) -> <span class="prelude-ty">Option</span><usize> { |
| <span class="kw">if </span><span class="self">self</span>.occupied == <span class="number">0 </span>{ |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| |
| <span class="comment">// Get the slot for now using Maths |
| </span><span class="kw">let </span>now_slot = (now / slot_range(<span class="self">self</span>.level)) <span class="kw">as </span>usize; |
| <span class="kw">let </span>occupied = <span class="self">self</span>.occupied.rotate_right(now_slot <span class="kw">as </span>u32); |
| <span class="kw">let </span>zeros = occupied.trailing_zeros() <span class="kw">as </span>usize; |
| <span class="kw">let </span>slot = (zeros + now_slot) % <span class="number">64</span>; |
| |
| <span class="prelude-val">Some</span>(slot) |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe fn </span>add_entry(<span class="kw-2">&mut </span><span class="self">self</span>, item: TimerHandle) { |
| <span class="kw">let </span>slot = slot_for(item.cached_when(), <span class="self">self</span>.level); |
| |
| <span class="self">self</span>.slot[slot].push_front(item); |
| |
| <span class="self">self</span>.occupied |= occupied_bit(slot); |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe fn </span>remove_entry(<span class="kw-2">&mut </span><span class="self">self</span>, item: NonNull<TimerShared>) { |
| <span class="kw">let </span>slot = slot_for(<span class="kw">unsafe </span>{ item.as_ref().cached_when() }, <span class="self">self</span>.level); |
| |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.slot[slot].remove(item) }; |
| <span class="kw">if </span><span class="self">self</span>.slot[slot].is_empty() { |
| <span class="comment">// The bit is currently set |
| </span><span class="macro">debug_assert!</span>(<span class="self">self</span>.occupied & occupied_bit(slot) != <span class="number">0</span>); |
| |
| <span class="comment">// Unset the bit |
| </span><span class="self">self</span>.occupied ^= occupied_bit(slot); |
| } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>take_slot(<span class="kw-2">&mut </span><span class="self">self</span>, slot: usize) -> EntryList { |
| <span class="self">self</span>.occupied &= !occupied_bit(slot); |
| |
| std::mem::take(<span class="kw-2">&mut </span><span class="self">self</span>.slot[slot]) |
| } |
| } |
| |
| <span class="kw">impl </span>fmt::Debug <span class="kw">for </span>Level { |
| <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">"Level"</span>) |
| .field(<span class="string">"occupied"</span>, <span class="kw-2">&</span><span class="self">self</span>.occupied) |
| .finish() |
| } |
| } |
| |
| <span class="kw">fn </span>occupied_bit(slot: usize) -> u64 { |
| <span class="number">1 </span><< slot |
| } |
| |
| <span class="kw">fn </span>slot_range(level: usize) -> u64 { |
| LEVEL_MULT.pow(level <span class="kw">as </span>u32) <span class="kw">as </span>u64 |
| } |
| |
| <span class="kw">fn </span>level_range(level: usize) -> u64 { |
| LEVEL_MULT <span class="kw">as </span>u64 * slot_range(level) |
| } |
| |
| <span class="doccomment">/// Converts a duration (milliseconds) and a level to a slot position. |
| </span><span class="kw">fn </span>slot_for(duration: u64, level: usize) -> usize { |
| ((duration >> (level * <span class="number">6</span>)) % LEVEL_MULT <span class="kw">as </span>u64) <span class="kw">as </span>usize |
| } |
| |
| <span class="attribute">#[cfg(all(test, not(loom)))] |
| </span><span class="kw">mod </span>test { |
| <span class="kw">use super</span>::<span class="kw-2">*</span>; |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_slot_for() { |
| <span class="kw">for </span>pos <span class="kw">in </span><span class="number">0</span>..<span class="number">64 </span>{ |
| <span class="macro">assert_eq!</span>(pos <span class="kw">as </span>usize, slot_for(pos, <span class="number">0</span>)); |
| } |
| |
| <span class="kw">for </span>level <span class="kw">in </span><span class="number">1</span>..<span class="number">5 </span>{ |
| <span class="kw">for </span>pos <span class="kw">in </span>level..<span class="number">64 </span>{ |
| <span class="kw">let </span>a = pos * <span class="number">64_usize</span>.pow(level <span class="kw">as </span>u32); |
| <span class="macro">assert_eq!</span>(pos <span class="kw">as </span>usize, slot_for(a <span class="kw">as </span>u64, level)); |
| } |
| } |
| } |
| } |
| </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> |
