| <!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/sync/mpsc/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="../../../../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> |
| <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> |
| <span id="347">347</span> |
| <span id="348">348</span> |
| <span id="349">349</span> |
| <span id="350">350</span> |
| <span id="351">351</span> |
| <span id="352">352</span> |
| <span id="353">353</span> |
| <span id="354">354</span> |
| <span id="355">355</span> |
| <span id="356">356</span> |
| <span id="357">357</span> |
| <span id="358">358</span> |
| <span id="359">359</span> |
| <span id="360">360</span> |
| <span id="361">361</span> |
| <span id="362">362</span> |
| <span id="363">363</span> |
| <span id="364">364</span> |
| <span id="365">365</span> |
| <span id="366">366</span> |
| <span id="367">367</span> |
| <span id="368">368</span> |
| <span id="369">369</span> |
| <span id="370">370</span> |
| <span id="371">371</span> |
| </pre><pre class="rust"><code><span class="doccomment">//! A concurrent, lock-free, FIFO list. |
| |
| </span><span class="kw">use </span><span class="kw">crate</span>::loom::sync::atomic::{AtomicPtr, AtomicUsize}; |
| <span class="kw">use </span><span class="kw">crate</span>::loom::thread; |
| <span class="kw">use </span><span class="kw">crate</span>::sync::mpsc::block::{<span class="self">self</span>, Block}; |
| |
| <span class="kw">use </span>std::fmt; |
| <span class="kw">use </span>std::ptr::NonNull; |
| <span class="kw">use </span>std::sync::atomic::Ordering::{AcqRel, Acquire, Relaxed, Release}; |
| |
| <span class="doccomment">/// List queue transmit handle. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Tx<T> { |
| <span class="doccomment">/// Tail in the `Block` mpmc list. |
| </span>block_tail: AtomicPtr<Block<T>>, |
| |
| <span class="doccomment">/// Position to push the next message. This references a block and offset |
| /// into the block. |
| </span>tail_position: AtomicUsize, |
| } |
| |
| <span class="doccomment">/// List queue receive handle |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">struct </span>Rx<T> { |
| <span class="doccomment">/// Pointer to the block being processed. |
| </span>head: NonNull<Block<T>>, |
| |
| <span class="doccomment">/// Next slot index to process. |
| </span>index: usize, |
| |
| <span class="doccomment">/// Pointer to the next block pending release. |
| </span>free_head: NonNull<Block<T>>, |
| } |
| |
| <span class="doccomment">/// Return value of `Rx::try_pop`. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">enum </span>TryPopResult<T> { |
| <span class="doccomment">/// Successfully popped a value. |
| </span><span class="prelude-val">Ok</span>(T), |
| <span class="doccomment">/// The channel is empty. |
| </span>Empty, |
| <span class="doccomment">/// The channel is empty and closed. |
| </span>Closed, |
| <span class="doccomment">/// The channel is not empty, but the first value is being written. |
| </span>Busy, |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>channel<T>() -> (Tx<T>, Rx<T>) { |
| <span class="comment">// Create the initial block shared between the tx and rx halves. |
| </span><span class="kw">let </span>initial_block = Block::new(<span class="number">0</span>); |
| <span class="kw">let </span>initial_block_ptr = Box::into_raw(initial_block); |
| |
| <span class="kw">let </span>tx = Tx { |
| block_tail: AtomicPtr::new(initial_block_ptr), |
| tail_position: AtomicUsize::new(<span class="number">0</span>), |
| }; |
| |
| <span class="kw">let </span>head = NonNull::new(initial_block_ptr).unwrap(); |
| |
| <span class="kw">let </span>rx = Rx { |
| head, |
| index: <span class="number">0</span>, |
| free_head: head, |
| }; |
| |
| (tx, rx) |
| } |
| |
| <span class="kw">impl</span><T> Tx<T> { |
| <span class="doccomment">/// Pushes a value into the list. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>push(<span class="kw-2">&</span><span class="self">self</span>, value: T) { |
| <span class="comment">// First, claim a slot for the value. `Acquire` is used here to |
| // synchronize with the `fetch_add` in `reclaim_blocks`. |
| </span><span class="kw">let </span>slot_index = <span class="self">self</span>.tail_position.fetch_add(<span class="number">1</span>, Acquire); |
| |
| <span class="comment">// Load the current block and write the value |
| </span><span class="kw">let </span>block = <span class="self">self</span>.find_block(slot_index); |
| |
| <span class="kw">unsafe </span>{ |
| <span class="comment">// Write the value to the block |
| </span>block.as_ref().write(slot_index, value); |
| } |
| } |
| |
| <span class="doccomment">/// Closes the send half of the list. |
| /// |
| /// Similar process as pushing a value, but instead of writing the value & |
| /// setting the ready flag, the TX_CLOSED flag is set on the block. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>close(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="comment">// First, claim a slot for the value. This is the last slot that will be |
| // claimed. |
| </span><span class="kw">let </span>slot_index = <span class="self">self</span>.tail_position.fetch_add(<span class="number">1</span>, Acquire); |
| |
| <span class="kw">let </span>block = <span class="self">self</span>.find_block(slot_index); |
| |
| <span class="kw">unsafe </span>{ block.as_ref().tx_close() } |
| } |
| |
| <span class="kw">fn </span>find_block(<span class="kw-2">&</span><span class="self">self</span>, slot_index: usize) -> NonNull<Block<T>> { |
| <span class="comment">// The start index of the block that contains `index`. |
| </span><span class="kw">let </span>start_index = block::start_index(slot_index); |
| |
| <span class="comment">// The index offset into the block |
| </span><span class="kw">let </span>offset = block::offset(slot_index); |
| |
| <span class="comment">// Load the current head of the block |
| </span><span class="kw">let </span><span class="kw-2">mut </span>block_ptr = <span class="self">self</span>.block_tail.load(Acquire); |
| |
| <span class="kw">let </span>block = <span class="kw">unsafe </span>{ <span class="kw-2">&*</span>block_ptr }; |
| |
| <span class="comment">// Calculate the distance between the tail ptr and the target block |
| </span><span class="kw">let </span>distance = block.distance(start_index); |
| |
| <span class="comment">// Decide if this call to `find_block` should attempt to update the |
| // `block_tail` pointer. |
| // |
| // Updating `block_tail` is not always performed in order to reduce |
| // contention. |
| // |
| // When set, as the routine walks the linked list, it attempts to update |
| // `block_tail`. If the update cannot be performed, `try_updating_tail` |
| // is unset. |
| </span><span class="kw">let </span><span class="kw-2">mut </span>try_updating_tail = distance > offset; |
| |
| <span class="comment">// Walk the linked list of blocks until the block with `start_index` is |
| // found. |
| </span><span class="kw">loop </span>{ |
| <span class="kw">let </span>block = <span class="kw">unsafe </span>{ <span class="kw-2">&</span>(<span class="kw-2">*</span>block_ptr) }; |
| |
| <span class="kw">if </span>block.is_at_index(start_index) { |
| <span class="kw">return unsafe </span>{ NonNull::new_unchecked(block_ptr) }; |
| } |
| |
| <span class="kw">let </span>next_block = block |
| .load_next(Acquire) |
| <span class="comment">// There is no allocated next block, grow the linked list. |
| </span>.unwrap_or_else(|| block.grow()); |
| |
| <span class="comment">// If the block is **not** final, then the tail pointer cannot be |
| // advanced any more. |
| </span>try_updating_tail &= block.is_final(); |
| |
| <span class="kw">if </span>try_updating_tail { |
| <span class="comment">// Advancing `block_tail` must happen when walking the linked |
| // list. `block_tail` may not advance passed any blocks that are |
| // not "final". At the point a block is finalized, it is unknown |
| // if there are any prior blocks that are unfinalized, which |
| // makes it impossible to advance `block_tail`. |
| // |
| // While walking the linked list, `block_tail` can be advanced |
| // as long as finalized blocks are traversed. |
| // |
| // Release ordering is used to ensure that any subsequent reads |
| // are able to see the memory pointed to by `block_tail`. |
| // |
| // Acquire is not needed as any "actual" value is not accessed. |
| // At this point, the linked list is walked to acquire blocks. |
| </span><span class="kw">if </span><span class="self">self |
| </span>.block_tail |
| .compare_exchange(block_ptr, next_block.as_ptr(), Release, Relaxed) |
| .is_ok() |
| { |
| <span class="comment">// Synchronize with any senders |
| </span><span class="kw">let </span>tail_position = <span class="self">self</span>.tail_position.fetch_add(<span class="number">0</span>, Release); |
| |
| <span class="kw">unsafe </span>{ |
| block.tx_release(tail_position); |
| } |
| } <span class="kw">else </span>{ |
| <span class="comment">// A concurrent sender is also working on advancing |
| // `block_tail` and this thread is falling behind. |
| // |
| // Stop trying to advance the tail pointer |
| </span>try_updating_tail = <span class="bool-val">false</span>; |
| } |
| } |
| |
| block_ptr = next_block.as_ptr(); |
| |
| thread::yield_now(); |
| } |
| } |
| |
| <span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">unsafe fn </span>reclaim_block(<span class="kw-2">&</span><span class="self">self</span>, <span class="kw-2">mut </span>block: NonNull<Block<T>>) { |
| <span class="comment">// The block has been removed from the linked list and ownership |
| // is reclaimed. |
| // |
| // Before dropping the block, see if it can be reused by |
| // inserting it back at the end of the linked list. |
| // |
| // First, reset the data |
| </span>block.as_mut().reclaim(); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>reused = <span class="bool-val">false</span>; |
| |
| <span class="comment">// Attempt to insert the block at the end |
| // |
| // Walk at most three times |
| // |
| </span><span class="kw">let </span>curr_ptr = <span class="self">self</span>.block_tail.load(Acquire); |
| |
| <span class="comment">// The pointer can never be null |
| </span><span class="macro">debug_assert!</span>(!curr_ptr.is_null()); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>curr = NonNull::new_unchecked(curr_ptr); |
| |
| <span class="comment">// TODO: Unify this logic with Block::grow |
| </span><span class="kw">for _ in </span><span class="number">0</span>..<span class="number">3 </span>{ |
| <span class="kw">match </span>curr.as_ref().try_push(<span class="kw-2">&mut </span>block, AcqRel, Acquire) { |
| <span class="prelude-val">Ok</span>(<span class="kw">_</span>) => { |
| reused = <span class="bool-val">true</span>; |
| <span class="kw">break</span>; |
| } |
| <span class="prelude-val">Err</span>(next) => { |
| curr = next; |
| } |
| } |
| } |
| |
| <span class="kw">if </span>!reused { |
| <span class="kw">let _ </span>= Box::from_raw(block.as_ptr()); |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T> fmt::Debug <span class="kw">for </span>Tx<T> { |
| <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">"Tx"</span>) |
| .field(<span class="string">"block_tail"</span>, <span class="kw-2">&</span><span class="self">self</span>.block_tail.load(Relaxed)) |
| .field(<span class="string">"tail_position"</span>, <span class="kw-2">&</span><span class="self">self</span>.tail_position.load(Relaxed)) |
| .finish() |
| } |
| } |
| |
| <span class="kw">impl</span><T> Rx<T> { |
| <span class="doccomment">/// Pops the next value off the queue. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>pop(<span class="kw-2">&mut </span><span class="self">self</span>, tx: <span class="kw-2">&</span>Tx<T>) -> <span class="prelude-ty">Option</span><block::Read<T>> { |
| <span class="comment">// Advance `head`, if needed |
| </span><span class="kw">if </span>!<span class="self">self</span>.try_advancing_head() { |
| <span class="kw">return </span><span class="prelude-val">None</span>; |
| } |
| |
| <span class="self">self</span>.reclaim_blocks(tx); |
| |
| <span class="kw">unsafe </span>{ |
| <span class="kw">let </span>block = <span class="self">self</span>.head.as_ref(); |
| |
| <span class="kw">let </span>ret = block.read(<span class="self">self</span>.index); |
| |
| <span class="kw">if let </span><span class="prelude-val">Some</span>(block::Read::Value(..)) = ret { |
| <span class="self">self</span>.index = <span class="self">self</span>.index.wrapping_add(<span class="number">1</span>); |
| } |
| |
| ret |
| } |
| } |
| |
| <span class="doccomment">/// Pops the next value off the queue, detecting whether the block |
| /// is busy or empty on failure. |
| /// |
| /// This function exists because `Rx::pop` can return `None` even if the |
| /// channel's queue contains a message that has been completely written. |
| /// This can happen if the fully delivered message is behind another message |
| /// that is in the middle of being written to the block, since the channel |
| /// can't return the messages out of order. |
| </span><span class="kw">pub</span>(<span class="kw">crate</span>) <span class="kw">fn </span>try_pop(<span class="kw-2">&mut </span><span class="self">self</span>, tx: <span class="kw-2">&</span>Tx<T>) -> TryPopResult<T> { |
| <span class="kw">let </span>tail_position = tx.tail_position.load(Acquire); |
| <span class="kw">let </span>result = <span class="self">self</span>.pop(tx); |
| |
| <span class="kw">match </span>result { |
| <span class="prelude-val">Some</span>(block::Read::Value(t)) => TryPopResult::Ok(t), |
| <span class="prelude-val">Some</span>(block::Read::Closed) => TryPopResult::Closed, |
| <span class="prelude-val">None </span><span class="kw">if </span>tail_position == <span class="self">self</span>.index => TryPopResult::Empty, |
| <span class="prelude-val">None </span>=> TryPopResult::Busy, |
| } |
| } |
| |
| <span class="doccomment">/// Tries advancing the block pointer to the block referenced by `self.index`. |
| /// |
| /// Returns `true` if successful, `false` if there is no next block to load. |
| </span><span class="kw">fn </span>try_advancing_head(<span class="kw-2">&mut </span><span class="self">self</span>) -> bool { |
| <span class="kw">let </span>block_index = block::start_index(<span class="self">self</span>.index); |
| |
| <span class="kw">loop </span>{ |
| <span class="kw">let </span>next_block = { |
| <span class="kw">let </span>block = <span class="kw">unsafe </span>{ <span class="self">self</span>.head.as_ref() }; |
| |
| <span class="kw">if </span>block.is_at_index(block_index) { |
| <span class="kw">return </span><span class="bool-val">true</span>; |
| } |
| |
| block.load_next(Acquire) |
| }; |
| |
| <span class="kw">let </span>next_block = <span class="kw">match </span>next_block { |
| <span class="prelude-val">Some</span>(next_block) => next_block, |
| <span class="prelude-val">None </span>=> { |
| <span class="kw">return </span><span class="bool-val">false</span>; |
| } |
| }; |
| |
| <span class="self">self</span>.head = next_block; |
| |
| thread::yield_now(); |
| } |
| } |
| |
| <span class="kw">fn </span>reclaim_blocks(<span class="kw-2">&mut </span><span class="self">self</span>, tx: <span class="kw-2">&</span>Tx<T>) { |
| <span class="kw">while </span><span class="self">self</span>.free_head != <span class="self">self</span>.head { |
| <span class="kw">unsafe </span>{ |
| <span class="comment">// Get a handle to the block that will be freed and update |
| // `free_head` to point to the next block. |
| </span><span class="kw">let </span>block = <span class="self">self</span>.free_head; |
| |
| <span class="kw">let </span>observed_tail_position = block.as_ref().observed_tail_position(); |
| |
| <span class="kw">let </span>required_index = <span class="kw">match </span>observed_tail_position { |
| <span class="prelude-val">Some</span>(i) => i, |
| <span class="prelude-val">None </span>=> <span class="kw">return</span>, |
| }; |
| |
| <span class="kw">if </span>required_index > <span class="self">self</span>.index { |
| <span class="kw">return</span>; |
| } |
| |
| <span class="comment">// We may read the next pointer with `Relaxed` ordering as it is |
| // guaranteed that the `reclaim_blocks` routine trails the `recv` |
| // routine. Any memory accessed by `reclaim_blocks` has already |
| // been acquired by `recv`. |
| </span><span class="kw">let </span>next_block = block.as_ref().load_next(Relaxed); |
| |
| <span class="comment">// Update the free list head |
| </span><span class="self">self</span>.free_head = next_block.unwrap(); |
| |
| <span class="comment">// Push the emptied block onto the back of the queue, making it |
| // available to senders. |
| </span>tx.reclaim_block(block); |
| } |
| |
| thread::yield_now(); |
| } |
| } |
| |
| <span class="doccomment">/// Effectively `Drop` all the blocks. Should only be called once, when |
| /// the list is dropping. |
| </span><span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">unsafe fn </span>free_blocks(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="macro">debug_assert_ne!</span>(<span class="self">self</span>.free_head, NonNull::dangling()); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>cur = <span class="prelude-val">Some</span>(<span class="self">self</span>.free_head); |
| |
| <span class="attribute">#[cfg(debug_assertions)] |
| </span>{ |
| <span class="comment">// to trigger the debug assert above so as to catch that we |
| // don't call `free_blocks` more than once. |
| </span><span class="self">self</span>.free_head = NonNull::dangling(); |
| <span class="self">self</span>.head = NonNull::dangling(); |
| } |
| |
| <span class="kw">while let </span><span class="prelude-val">Some</span>(block) = cur { |
| cur = block.as_ref().load_next(Relaxed); |
| drop(Box::from_raw(block.as_ptr())); |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T> fmt::Debug <span class="kw">for </span>Rx<T> { |
| <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">"Rx"</span>) |
| .field(<span class="string">"head"</span>, <span class="kw-2">&</span><span class="self">self</span>.head) |
| .field(<span class="string">"index"</span>, <span class="kw-2">&</span><span class="self">self</span>.index) |
| .field(<span class="string">"free_head"</span>, <span class="kw-2">&</span><span class="self">self</span>.free_head) |
| .finish() |
| } |
| } |
| </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> |
