| <!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/arc-swap-1.6.0/src/debt/fast.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>fast.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="../../../arc_swap/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="../../../arc_swap/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> |
| <span id="2">2</span> |
| <span id="3">3</span> |
| <span id="4">4</span> |
| <span id="5">5</span> |
| <span id="6">6</span> |
| <span id="7">7</span> |
| <span id="8">8</span> |
| <span id="9">9</span> |
| <span id="10">10</span> |
| <span id="11">11</span> |
| <span id="12">12</span> |
| <span id="13">13</span> |
| <span id="14">14</span> |
| <span id="15">15</span> |
| <span id="16">16</span> |
| <span id="17">17</span> |
| <span id="18">18</span> |
| <span id="19">19</span> |
| <span id="20">20</span> |
| <span id="21">21</span> |
| <span id="22">22</span> |
| <span id="23">23</span> |
| <span id="24">24</span> |
| <span id="25">25</span> |
| <span id="26">26</span> |
| <span id="27">27</span> |
| <span id="28">28</span> |
| <span id="29">29</span> |
| <span id="30">30</span> |
| <span id="31">31</span> |
| <span id="32">32</span> |
| <span id="33">33</span> |
| <span id="34">34</span> |
| <span id="35">35</span> |
| <span id="36">36</span> |
| <span id="37">37</span> |
| <span id="38">38</span> |
| <span id="39">39</span> |
| <span id="40">40</span> |
| <span id="41">41</span> |
| <span id="42">42</span> |
| <span id="43">43</span> |
| <span id="44">44</span> |
| <span id="45">45</span> |
| <span id="46">46</span> |
| <span id="47">47</span> |
| <span id="48">48</span> |
| <span id="49">49</span> |
| <span id="50">50</span> |
| <span id="51">51</span> |
| <span id="52">52</span> |
| <span id="53">53</span> |
| <span id="54">54</span> |
| <span id="55">55</span> |
| <span id="56">56</span> |
| <span id="57">57</span> |
| <span id="58">58</span> |
| <span id="59">59</span> |
| <span id="60">60</span> |
| <span id="61">61</span> |
| <span id="62">62</span> |
| <span id="63">63</span> |
| <span id="64">64</span> |
| <span id="65">65</span> |
| <span id="66">66</span> |
| <span id="67">67</span> |
| <span id="68">68</span> |
| <span id="69">69</span> |
| <span id="70">70</span> |
| <span id="71">71</span> |
| <span id="72">72</span> |
| <span id="73">73</span> |
| <span id="74">74</span> |
| <span id="75">75</span> |
| <span id="76">76</span> |
| </pre><pre class="rust"><code><span class="doccomment">//! The fast slots for the primary strategy. |
| //! |
| //! They are faster, but fallible (in case the slots run out or if there's a collision with a |
| //! writer thread, this gives up and falls back to secondary strategy). |
| //! |
| //! They are based on hazard pointer ideas. To acquire one, the pointer is loaded, stored in the |
| //! slot and the debt is confirmed by loading it again and checking it is the same. |
| //! |
| //! # Orderings |
| //! |
| //! We ensure just one thing here. Since we do both the acquisition of the slot and the exchange of |
| //! the pointer in the writer with SeqCst, we are guaranteed to either see the change in case it |
| //! hits somewhere in between the two reads of the pointer, or to have successfully acquired it |
| //! before the change and before any cleanup of the old pointer happened (in which case we know the |
| //! writer will see our debt). |
| |
| </span><span class="kw">use </span>std::cell::Cell; |
| <span class="kw">use </span>std::slice::Iter; |
| <span class="kw">use </span>std::sync::atomic::Ordering::<span class="kw-2">*</span>; |
| |
| <span class="kw">use </span><span class="kw">super</span>::Debt; |
| |
| <span class="kw">const </span>DEBT_SLOT_CNT: usize = <span class="number">8</span>; |
| |
| <span class="doccomment">/// Thread-local information for the [`Slots`] |
| </span><span class="attribute">#[derive(Default)] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Local { |
| <span class="comment">// The next slot in round-robin rotation. Heuristically tries to balance the load across them |
| // instead of having all of them stuffed towards the start of the array which gets |
| // unsuccessfully iterated through every time. |
| </span>offset: Cell<usize>, |
| } |
| |
| <span class="doccomment">/// Bunch of fast debt slots. |
| </span><span class="attribute">#[derive(Default)] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct </span>Slots([Debt; DEBT_SLOT_CNT]); |
| |
| <span class="kw">impl </span>Slots { |
| <span class="doccomment">/// Try to allocate one slot and get the pointer in it. |
| /// |
| /// Fails if there are no free slots. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>get_debt(<span class="kw-2">&</span><span class="self">self</span>, ptr: usize, local: <span class="kw-2">&</span>Local) -> <span class="prelude-ty">Option</span><<span class="kw-2">&</span>Debt> { |
| <span class="comment">// Trick with offsets: we rotate through the slots (save the value from last time) |
| // so successive leases are likely to succeed on the first attempt (or soon after) |
| // instead of going through the list of already held ones. |
| </span><span class="kw">let </span>offset = local.offset.get(); |
| <span class="kw">let </span>len = <span class="self">self</span>.<span class="number">0</span>.len(); |
| <span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..len { |
| <span class="kw">let </span>i = (i + offset) % len; |
| <span class="comment">// Note: the indexing check is almost certainly optimised out because the len |
| // is used above. And using .get_unchecked was actually *slower*. |
| </span><span class="kw">let </span>slot = <span class="kw-2">&</span><span class="self">self</span>.<span class="number">0</span>[i]; |
| <span class="kw">if </span>slot.<span class="number">0</span>.load(Relaxed) == Debt::NONE { |
| <span class="comment">// We are allowed to split into the check and acquiring the debt. That's because we |
| // are the only ones allowed to change NONE to something else. But we still need a |
| // read-write operation wit SeqCst on it :-( |
| </span><span class="kw">let </span>old = slot.<span class="number">0</span>.swap(ptr, SeqCst); |
| <span class="macro">debug_assert_eq!</span>(Debt::NONE, old); |
| local.offset.set(i + <span class="number">1</span>); |
| <span class="kw">return </span><span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="self">self</span>.<span class="number">0</span>[i]); |
| } |
| } |
| <span class="prelude-val">None |
| </span>} |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'a</span>> IntoIterator <span class="kw">for </span><span class="kw-2">&</span><span class="lifetime">'a </span>Slots { |
| <span class="kw">type </span>Item = <span class="kw-2">&</span><span class="lifetime">'a </span>Debt; |
| |
| <span class="kw">type </span>IntoIter = Iter<<span class="lifetime">'a</span>, Debt>; |
| |
| <span class="kw">fn </span>into_iter(<span class="self">self</span>) -> <span class="self">Self</span>::IntoIter { |
| <span class="self">self</span>.<span class="number">0</span>.iter() |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="arc_swap" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
