Google Git
Sign in
apache / incubator-teaclave-website / refs/heads/asf-site / . / api-docs / crates-enclave / src / arc_swap / debt / list.rs.html
blob: 277390ad23589225bcf8b72e9d6f12f33bf3eeb2 [file] [log] [blame]
<!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/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="../../../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>
<span id="77">77</span>
<span id="78">78</span>
<span id="79">79</span>
<span id="80">80</span>
<span id="81">81</span>
<span id="82">82</span>
<span id="83">83</span>
<span id="84">84</span>
<span id="85">85</span>
<span id="86">86</span>
<span id="87">87</span>
<span id="88">88</span>
<span id="89">89</span>
<span id="90">90</span>
<span id="91">91</span>
<span id="92">92</span>
<span id="93">93</span>
<span id="94">94</span>
<span id="95">95</span>
<span id="96">96</span>
<span id="97">97</span>
<span id="98">98</span>
<span id="99">99</span>
<span id="100">100</span>
<span id="101">101</span>
<span id="102">102</span>
<span id="103">103</span>
<span id="104">104</span>
<span id="105">105</span>
<span id="106">106</span>
<span id="107">107</span>
<span id="108">108</span>
<span id="109">109</span>
<span id="110">110</span>
<span id="111">111</span>
<span id="112">112</span>
<span id="113">113</span>
<span id="114">114</span>
<span id="115">115</span>
<span id="116">116</span>
<span id="117">117</span>
<span id="118">118</span>
<span id="119">119</span>
<span id="120">120</span>
<span id="121">121</span>
<span id="122">122</span>
<span id="123">123</span>
<span id="124">124</span>
<span id="125">125</span>
<span id="126">126</span>
<span id="127">127</span>
<span id="128">128</span>
<span id="129">129</span>
<span id="130">130</span>
<span id="131">131</span>
<span id="132">132</span>
<span id="133">133</span>
<span id="134">134</span>
<span id="135">135</span>
<span id="136">136</span>
<span id="137">137</span>
<span id="138">138</span>
<span id="139">139</span>
<span id="140">140</span>
<span id="141">141</span>
<span id="142">142</span>
<span id="143">143</span>
<span id="144">144</span>
<span id="145">145</span>
<span id="146">146</span>
<span id="147">147</span>
<span id="148">148</span>
<span id="149">149</span>
<span id="150">150</span>
<span id="151">151</span>
<span id="152">152</span>
<span id="153">153</span>
<span id="154">154</span>
<span id="155">155</span>
<span id="156">156</span>
<span id="157">157</span>
<span id="158">158</span>
<span id="159">159</span>
<span id="160">160</span>
<span id="161">161</span>
<span id="162">162</span>
<span id="163">163</span>
<span id="164">164</span>
<span id="165">165</span>
<span id="166">166</span>
<span id="167">167</span>
<span id="168">168</span>
<span id="169">169</span>
<span id="170">170</span>
<span id="171">171</span>
<span id="172">172</span>
<span id="173">173</span>
<span id="174">174</span>
<span id="175">175</span>
<span id="176">176</span>
<span id="177">177</span>
<span id="178">178</span>
<span id="179">179</span>
<span id="180">180</span>
<span id="181">181</span>
<span id="182">182</span>
<span id="183">183</span>
<span id="184">184</span>
<span id="185">185</span>
<span id="186">186</span>
<span id="187">187</span>
<span id="188">188</span>
<span id="189">189</span>
<span id="190">190</span>
<span id="191">191</span>
<span id="192">192</span>
<span id="193">193</span>
<span id="194">194</span>
<span id="195">195</span>
<span id="196">196</span>
<span id="197">197</span>
<span id="198">198</span>
<span id="199">199</span>
<span id="200">200</span>
<span id="201">201</span>
<span id="202">202</span>
<span id="203">203</span>
<span id="204">204</span>
<span id="205">205</span>
<span id="206">206</span>
<span id="207">207</span>
<span id="208">208</span>
<span id="209">209</span>
<span id="210">210</span>
<span id="211">211</span>
<span id="212">212</span>
<span id="213">213</span>
<span id="214">214</span>
<span id="215">215</span>
<span id="216">216</span>
<span id="217">217</span>
<span id="218">218</span>
<span id="219">219</span>
<span id="220">220</span>
<span id="221">221</span>
<span id="222">222</span>
<span id="223">223</span>
<span id="224">224</span>
<span id="225">225</span>
<span id="226">226</span>
<span id="227">227</span>
<span id="228">228</span>
<span id="229">229</span>
<span id="230">230</span>
<span id="231">231</span>
<span id="232">232</span>
<span id="233">233</span>
<span id="234">234</span>
<span id="235">235</span>
<span id="236">236</span>
<span id="237">237</span>
<span id="238">238</span>
<span id="239">239</span>
<span id="240">240</span>
<span id="241">241</span>
<span id="242">242</span>
<span id="243">243</span>
<span id="244">244</span>
<span id="245">245</span>
<span id="246">246</span>
<span id="247">247</span>
<span id="248">248</span>
<span id="249">249</span>
<span id="250">250</span>
<span id="251">251</span>
<span id="252">252</span>
<span id="253">253</span>
<span id="254">254</span>
<span id="255">255</span>
<span id="256">256</span>
<span id="257">257</span>
<span id="258">258</span>
<span id="259">259</span>
<span id="260">260</span>
<span id="261">261</span>
<span id="262">262</span>
<span id="263">263</span>
<span id="264">264</span>
<span id="265">265</span>
<span id="266">266</span>
<span id="267">267</span>
<span id="268">268</span>
<span id="269">269</span>
<span id="270">270</span>
<span id="271">271</span>
<span id="272">272</span>
<span id="273">273</span>
<span id="274">274</span>
<span id="275">275</span>
<span id="276">276</span>
<span id="277">277</span>
<span id="278">278</span>
<span id="279">279</span>
<span id="280">280</span>
<span id="281">281</span>
<span id="282">282</span>
<span id="283">283</span>
<span id="284">284</span>
<span id="285">285</span>
<span id="286">286</span>
<span id="287">287</span>
<span id="288">288</span>
<span id="289">289</span>
<span id="290">290</span>
<span id="291">291</span>
<span id="292">292</span>
<span id="293">293</span>
<span id="294">294</span>
<span id="295">295</span>
<span id="296">296</span>
<span id="297">297</span>
<span id="298">298</span>
<span id="299">299</span>
<span id="300">300</span>
<span id="301">301</span>
<span id="302">302</span>
<span id="303">303</span>
<span id="304">304</span>
<span id="305">305</span>
<span id="306">306</span>
<span id="307">307</span>
<span id="308">308</span>
<span id="309">309</span>
<span id="310">310</span>
<span id="311">311</span>
<span id="312">312</span>
<span id="313">313</span>
<span id="314">314</span>
<span id="315">315</span>
<span id="316">316</span>
<span id="317">317</span>
<span id="318">318</span>
<span id="319">319</span>
<span id="320">320</span>
<span id="321">321</span>
<span id="322">322</span>
<span id="323">323</span>
<span id="324">324</span>
<span id="325">325</span>
<span id="326">326</span>
<span id="327">327</span>
<span id="328">328</span>
<span id="329">329</span>
<span id="330">330</span>
<span id="331">331</span>
<span id="332">332</span>
<span id="333">333</span>
<span id="334">334</span>
<span id="335">335</span>
<span id="336">336</span>
<span id="337">337</span>
<span id="338">338</span>
<span id="339">339</span>
<span id="340">340</span>
<span id="341">341</span>
<span id="342">342</span>
<span id="343">343</span>
<span id="344">344</span>
<span id="345">345</span>
<span id="346">346</span>
</pre><pre class="rust"><code><span class="doccomment">//! A linked list of debt nodes.
//!
//! A node may or may not be owned by a thread. Reader debts are allocated in its owned node,
//! writer walks everything (but may also use some owned values).
//!
//! The list is prepend-only ‒ if thread dies, the node lives on (and can be claimed by another
//! thread later on). This makes the implementation much simpler, since everything here is
//! `&#39;static` and we don&#39;t have to care about knowing when to free stuff.
//!
//! The nodes contain both the fast primary slots and a secondary fallback ones.
//!
//! # Synchronization
//!
//! We synchronize several things here.
//!
//! The addition of nodes is synchronized through the head (Load on each read, AcqReal on each
//! attempt to add another node). Note that certain parts never change after that (they aren&#39;t even
//! atomic) and other things that do change take care of themselves (the debt slots have their own
//! synchronization, etc).
//!
//! The ownership is acquire-release lock pattern.
//!
//! Similar, the counting of active writers is an acquire-release lock pattern.
//!
//! We also do release-acquire &quot;send&quot; from the start-cooldown to check-cooldown to make sure we see
//! at least as up to date value of the writers as when the cooldown started. That we if we see 0,
//! we know it must have happened since then.
</span><span class="kw">use </span>std::cell::Cell;
<span class="kw">use </span>std::ptr;
<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>std::sync::atomic::{AtomicPtr, AtomicUsize};
<span class="kw">use </span><span class="kw">super</span>::fast::{Local <span class="kw">as </span>FastLocal, Slots <span class="kw">as </span>FastSlots};
<span class="kw">use </span><span class="kw">super</span>::helping::{Local <span class="kw">as </span>HelpingLocal, Slots <span class="kw">as </span>HelpingSlots};
<span class="kw">use </span><span class="kw">super</span>::Debt;
<span class="kw">use </span><span class="kw">crate</span>::RefCnt;
<span class="kw">const </span>NODE_UNUSED: usize = <span class="number">0</span>;
<span class="kw">const </span>NODE_USED: usize = <span class="number">1</span>;
<span class="kw">const </span>NODE_COOLDOWN: usize = <span class="number">2</span>;
<span class="doccomment">/// The head of the debt linked list.
</span><span class="kw">static </span>LIST_HEAD: AtomicPtr&lt;Node&gt; = AtomicPtr::new(ptr::null_mut());
<span class="kw">pub struct </span>NodeReservation&lt;<span class="lifetime">&#39;a</span>&gt;(<span class="kw-2">&amp;</span><span class="lifetime">&#39;a </span>Node);
<span class="kw">impl </span>Drop <span class="kw">for </span>NodeReservation&lt;<span class="lifetime">&#39;_</span>&gt; {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="self">self</span>.<span class="number">0</span>.active_writers.fetch_sub(<span class="number">1</span>, Release);
}
}
<span class="doccomment">/// One thread-local node for debts.
</span><span class="attribute">#[repr(C, align(<span class="number">64</span>))]
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Node {
fast: FastSlots,
helping: HelpingSlots,
in_use: AtomicUsize,
<span class="comment">// Next node in the list.
//
// It is a pointer because we touch it before synchronization (we don&#39;t _dereference_ it before
// synchronization, only manipulate the pointer itself). That is illegal according to strict
// interpretation of the rules by MIRI on references.
</span>next: <span class="kw-2">*const </span>Node,
active_writers: AtomicUsize,
}
<span class="kw">impl </span>Default <span class="kw">for </span>Node {
<span class="kw">fn </span>default() -&gt; <span class="self">Self </span>{
Node {
fast: FastSlots::default(),
helping: HelpingSlots::default(),
in_use: AtomicUsize::new(NODE_USED),
next: ptr::null(),
active_writers: AtomicUsize::new(<span class="number">0</span>),
}
}
}
<span class="kw">impl </span>Node {
<span class="doccomment">/// Goes through the debt linked list.
///
/// This traverses the linked list, calling the closure on each node. If the closure returns
/// `Some`, it terminates with that value early, otherwise it runs to the end.
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>traverse&lt;R, F: FnMut(<span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Node) -&gt; <span class="prelude-ty">Option</span>&lt;R&gt;&gt;(<span class="kw-2">mut </span>f: F) -&gt; <span class="prelude-ty">Option</span>&lt;R&gt; {
<span class="comment">// Acquire ‒ we want to make sure we read the correct version of data at the end of the
// pointer. Any write to the DEBT_HEAD is with Release.
//
// Furthermore, we need to see the newest version of the list in case we examine the debts
// - if a new one is added recently, we don&#39;t want a stale read -&gt; SeqCst.
//
// Note that the other pointers in the chain never change and are *ordinary* pointers. The
// whole linked list is synchronized through the head.
</span><span class="kw">let </span><span class="kw-2">mut </span>current = <span class="kw">unsafe </span>{ LIST_HEAD.load(SeqCst).as_ref() };
<span class="kw">while let </span><span class="prelude-val">Some</span>(node) = current {
<span class="kw">let </span>result = f(node);
<span class="kw">if </span>result.is_some() {
<span class="kw">return </span>result;
}
current = <span class="kw">unsafe </span>{ node.next.as_ref() };
}
<span class="prelude-val">None
</span>}
<span class="doccomment">/// Put the current thread node into cooldown
</span><span class="kw">fn </span>start_cooldown(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="comment">// Trick: Make sure we have an up to date value of the active_writers in this thread, so we
// can properly release it below.
</span><span class="kw">let </span>_reservation = <span class="self">self</span>.reserve_writer();
<span class="macro">assert_eq!</span>(NODE_USED, <span class="self">self</span>.in_use.swap(NODE_COOLDOWN, Release));
}
<span class="doccomment">/// Perform a cooldown if the node is ready.
///
/// See the ABA protection at the [helping].
</span><span class="kw">fn </span>check_cooldown(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="comment">// Check if the node is in cooldown, for two reasons:
// * Skip most of nodes fast, without dealing with them.
// * More importantly, sync the value of active_writers to be at least the value when the
// cooldown started. That way we know the 0 we observe happened some time after
// start_cooldown.
</span><span class="kw">if </span><span class="self">self</span>.in_use.load(Acquire) == NODE_COOLDOWN {
<span class="comment">// The rest can be nicely relaxed ‒ no memory is being synchronized by these
// operations. We just see an up to date 0 and allow someone (possibly us) to claim the
// node later on.
</span><span class="kw">if </span><span class="self">self</span>.active_writers.load(Relaxed) == <span class="number">0 </span>{
<span class="kw">let _ </span>= <span class="self">self
</span>.in_use
.compare_exchange(NODE_COOLDOWN, NODE_UNUSED, Relaxed, Relaxed);
}
}
}
<span class="doccomment">/// Mark this node that a writer is currently playing with it.
</span><span class="kw">pub fn </span>reserve_writer(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; NodeReservation {
<span class="self">self</span>.active_writers.fetch_add(<span class="number">1</span>, Acquire);
NodeReservation(<span class="self">self</span>)
}
<span class="doccomment">/// &quot;Allocate&quot; a node.
///
/// Either a new one is created, or previous one is reused. The node is claimed to become
/// in_use.
</span><span class="kw">fn </span>get() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span><span class="self">Self </span>{
<span class="comment">// Try to find an unused one in the chain and reuse it.
</span><span class="self">Self</span>::traverse(|node| {
node.check_cooldown();
<span class="kw">if </span>node
.in_use
<span class="comment">// We claim a unique control over the generation and the right to write to slots if
// they are NO_DEPT
</span>.compare_exchange(NODE_UNUSED, NODE_USED, SeqCst, Relaxed)
.is_ok()
{
<span class="prelude-val">Some</span>(node)
} <span class="kw">else </span>{
<span class="prelude-val">None
</span>}
})
<span class="comment">// If that didn&#39;t work, create a new one and prepend to the list.
</span>.unwrap_or_else(|| {
<span class="kw">let </span>node = Box::leak(Box::&lt;Node&gt;::default());
node.helping.init();
<span class="comment">// We don&#39;t want to read any data in addition to the head, Relaxed is fine
// here.
//
// We do need to release the data to others, but for that, we acquire in the
// compare_exchange below.
</span><span class="kw">let </span><span class="kw-2">mut </span>head = LIST_HEAD.load(Relaxed);
<span class="kw">loop </span>{
node.next = head;
<span class="kw">if let </span><span class="prelude-val">Err</span>(old) = LIST_HEAD.compare_exchange_weak(
head, node,
<span class="comment">// We need to release *the whole chain* here. For that, we need to
// acquire it first.
//
// SeqCst because we need to make sure it is properly set &quot;before&quot; we do
// anything to the debts.
</span>SeqCst, Relaxed, <span class="comment">// Nothing changed, go next round of the loop.
</span>) {
head = old;
} <span class="kw">else </span>{
<span class="kw">return </span>node;
}
}
})
}
<span class="doccomment">/// Iterate over the fast slots.
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>fast_slots(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; Iter&lt;Debt&gt; {
<span class="self">self</span>.fast.into_iter()
}
<span class="doccomment">/// Access the helping slot.
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>helping_slot(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="kw-2">&amp;</span>Debt {
<span class="self">self</span>.helping.slot()
}
}
<span class="doccomment">/// A wrapper around a node pointer, to un-claim the node on thread shutdown.
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>LocalNode {
<span class="doccomment">/// Node for this thread, if any.
///
/// We don&#39;t necessarily have to own one, but if we don&#39;t, we&#39;ll get one before the first use.
</span>node: Cell&lt;<span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Node&gt;&gt;,
<span class="doccomment">/// Thread-local data for the fast slots.
</span>fast: FastLocal,
<span class="doccomment">/// Thread local data for the helping strategy.
</span>helping: HelpingLocal,
}
<span class="kw">impl </span>LocalNode {
<span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>with&lt;R, F: FnOnce(<span class="kw-2">&amp;</span>LocalNode) -&gt; R&gt;(f: F) -&gt; R {
<span class="kw">let </span>f = Cell::new(<span class="prelude-val">Some</span>(f));
THREAD_HEAD
.try_with(|head| {
<span class="kw">if </span>head.node.get().is_none() {
head.node.set(<span class="prelude-val">Some</span>(Node::get()));
}
<span class="kw">let </span>f = f.take().unwrap();
f(head)
})
<span class="comment">// During the application shutdown, the thread local storage may be already
// deallocated. In that case, the above fails but we still need something. So we just
// find or allocate a node and use it just once.
//
// Note that the situation should be very very rare and not happen often, so the slower
// performance doesn&#39;t matter that much.
</span>.unwrap_or_else(|<span class="kw">_</span>| {
<span class="kw">let </span>tmp_node = LocalNode {
node: Cell::new(<span class="prelude-val">Some</span>(Node::get())),
fast: FastLocal::default(),
helping: HelpingLocal::default(),
};
<span class="kw">let </span>f = f.take().unwrap();
f(<span class="kw-2">&amp;</span>tmp_node)
<span class="comment">// Drop of tmp_node -&gt; sends the node we just used into cooldown.
</span>})
}
<span class="doccomment">/// Creates a new debt.
///
/// This stores the debt of the given pointer (untyped, casted into an usize) and returns a
/// reference to that slot, or gives up with `None` if all the slots are currently full.
</span><span class="attribute">#[inline]
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new_fast(<span class="kw-2">&amp;</span><span class="self">self</span>, ptr: usize) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Debt&gt; {
<span class="kw">let </span>node = <span class="kw-2">&amp;</span><span class="self">self</span>.node.get().expect(<span class="string">&quot;LocalNode::with ensures it is set&quot;</span>);
<span class="macro">debug_assert_eq!</span>(node.in_use.load(Relaxed), NODE_USED);
node.fast.get_debt(ptr, <span class="kw-2">&amp;</span><span class="self">self</span>.fast)
}
<span class="doccomment">/// Initializes a helping slot transaction.
///
/// Returns the generation (with tag).
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>new_helping(<span class="kw-2">&amp;</span><span class="self">self</span>, ptr: usize) -&gt; usize {
<span class="kw">let </span>node = <span class="kw-2">&amp;</span><span class="self">self</span>.node.get().expect(<span class="string">&quot;LocalNode::with ensures it is set&quot;</span>);
<span class="macro">debug_assert_eq!</span>(node.in_use.load(Relaxed), NODE_USED);
<span class="kw">let </span>(gen, discard) = node.helping.get_debt(ptr, <span class="kw-2">&amp;</span><span class="self">self</span>.helping);
<span class="kw">if </span>discard {
<span class="comment">// Too many generations happened, make sure the writers give the poor node a break for
// a while so they don&#39;t observe the generation wrapping around.
</span>node.start_cooldown();
<span class="self">self</span>.node.take();
}
gen
}
<span class="doccomment">/// Confirm the helping transaction.
///
/// The generation comes from previous new_helping.
///
/// Will either return a debt with the pointer, or a debt to pay and a replacement (already
/// protected) address.
</span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>confirm_helping(
<span class="kw-2">&amp;</span><span class="self">self</span>,
gen: usize,
ptr: usize,
) -&gt; <span class="prelude-ty">Result</span>&lt;<span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Debt, (<span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Debt, usize)&gt; {
<span class="kw">let </span>node = <span class="kw-2">&amp;</span><span class="self">self</span>.node.get().expect(<span class="string">&quot;LocalNode::with ensures it is set&quot;</span>);
<span class="macro">debug_assert_eq!</span>(node.in_use.load(Relaxed), NODE_USED);
<span class="kw">let </span>slot = node.helping_slot();
node.helping
.confirm(gen, ptr)
.map(|()| slot)
.map_err(|repl| (slot, repl))
}
<span class="doccomment">/// The writer side of a helping slot.
///
/// This potentially helps the `who` node (uses self as the local node, which must be
/// different) by loading the address that one is trying to load.
</span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn </span>help&lt;R, T&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, who: <span class="kw-2">&amp;</span>Node, storage_addr: usize, replacement: <span class="kw-2">&amp;</span>R)
<span class="kw">where
</span>T: RefCnt,
R: Fn() -&gt; T,
{
<span class="kw">let </span>node = <span class="kw-2">&amp;</span><span class="self">self</span>.node.get().expect(<span class="string">&quot;LocalNode::with ensures it is set&quot;</span>);
<span class="macro">debug_assert_eq!</span>(node.in_use.load(Relaxed), NODE_USED);
node.helping.help(<span class="kw-2">&amp;</span>who.helping, storage_addr, replacement)
}
}
<span class="kw">impl </span>Drop <span class="kw">for </span>LocalNode {
<span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(node) = <span class="self">self</span>.node.get() {
<span class="comment">// Release - syncing writes/ownership of this Node
</span>node.start_cooldown();
}
}
}
<span class="macro">thread_local! </span>{
<span class="doccomment">/// A debt node assigned to this thread.
</span><span class="kw">static </span>THREAD_HEAD: LocalNode = LocalNode {
node: Cell::new(<span class="prelude-val">None</span>),
fast: FastLocal::default(),
helping: HelpingLocal::default(),
};
}
<span class="attribute">#[cfg(test)]
</span><span class="kw">mod </span>tests {
<span class="kw">use super</span>::<span class="kw-2">*</span>;
<span class="kw">impl </span>Node {
<span class="kw">fn </span>is_empty(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; bool {
<span class="self">self</span>.fast_slots()
.chain(std::iter::once(<span class="self">self</span>.helping_slot()))
.all(|d| d.<span class="number">0</span>.load(Relaxed) == Debt::NONE)
}
<span class="kw">fn </span>get_thread() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span><span class="self">Self </span>{
LocalNode::with(|h| h.node.get().unwrap())
}
}
<span class="doccomment">/// A freshly acquired thread local node is empty.
</span><span class="attribute">#[test]
</span><span class="kw">fn </span>new_empty() {
<span class="macro">assert!</span>(Node::get_thread().is_empty());
}
}
</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>