| <!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/spin-0.5.2/src/rw_lock.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>rw_lock.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="../../spin/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="../../spin/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> |
| <span id="372">372</span> |
| <span id="373">373</span> |
| <span id="374">374</span> |
| <span id="375">375</span> |
| <span id="376">376</span> |
| <span id="377">377</span> |
| <span id="378">378</span> |
| <span id="379">379</span> |
| <span id="380">380</span> |
| <span id="381">381</span> |
| <span id="382">382</span> |
| <span id="383">383</span> |
| <span id="384">384</span> |
| <span id="385">385</span> |
| <span id="386">386</span> |
| <span id="387">387</span> |
| <span id="388">388</span> |
| <span id="389">389</span> |
| <span id="390">390</span> |
| <span id="391">391</span> |
| <span id="392">392</span> |
| <span id="393">393</span> |
| <span id="394">394</span> |
| <span id="395">395</span> |
| <span id="396">396</span> |
| <span id="397">397</span> |
| <span id="398">398</span> |
| <span id="399">399</span> |
| <span id="400">400</span> |
| <span id="401">401</span> |
| <span id="402">402</span> |
| <span id="403">403</span> |
| <span id="404">404</span> |
| <span id="405">405</span> |
| <span id="406">406</span> |
| <span id="407">407</span> |
| <span id="408">408</span> |
| <span id="409">409</span> |
| <span id="410">410</span> |
| <span id="411">411</span> |
| <span id="412">412</span> |
| <span id="413">413</span> |
| <span id="414">414</span> |
| <span id="415">415</span> |
| <span id="416">416</span> |
| <span id="417">417</span> |
| <span id="418">418</span> |
| <span id="419">419</span> |
| <span id="420">420</span> |
| <span id="421">421</span> |
| <span id="422">422</span> |
| <span id="423">423</span> |
| <span id="424">424</span> |
| <span id="425">425</span> |
| <span id="426">426</span> |
| <span id="427">427</span> |
| <span id="428">428</span> |
| <span id="429">429</span> |
| <span id="430">430</span> |
| <span id="431">431</span> |
| <span id="432">432</span> |
| <span id="433">433</span> |
| <span id="434">434</span> |
| <span id="435">435</span> |
| <span id="436">436</span> |
| <span id="437">437</span> |
| <span id="438">438</span> |
| <span id="439">439</span> |
| <span id="440">440</span> |
| <span id="441">441</span> |
| <span id="442">442</span> |
| <span id="443">443</span> |
| <span id="444">444</span> |
| <span id="445">445</span> |
| <span id="446">446</span> |
| <span id="447">447</span> |
| <span id="448">448</span> |
| <span id="449">449</span> |
| <span id="450">450</span> |
| <span id="451">451</span> |
| <span id="452">452</span> |
| <span id="453">453</span> |
| <span id="454">454</span> |
| <span id="455">455</span> |
| <span id="456">456</span> |
| <span id="457">457</span> |
| <span id="458">458</span> |
| <span id="459">459</span> |
| <span id="460">460</span> |
| <span id="461">461</span> |
| <span id="462">462</span> |
| <span id="463">463</span> |
| <span id="464">464</span> |
| <span id="465">465</span> |
| <span id="466">466</span> |
| <span id="467">467</span> |
| <span id="468">468</span> |
| <span id="469">469</span> |
| <span id="470">470</span> |
| <span id="471">471</span> |
| <span id="472">472</span> |
| <span id="473">473</span> |
| <span id="474">474</span> |
| <span id="475">475</span> |
| <span id="476">476</span> |
| <span id="477">477</span> |
| <span id="478">478</span> |
| <span id="479">479</span> |
| <span id="480">480</span> |
| <span id="481">481</span> |
| <span id="482">482</span> |
| <span id="483">483</span> |
| <span id="484">484</span> |
| <span id="485">485</span> |
| <span id="486">486</span> |
| <span id="487">487</span> |
| <span id="488">488</span> |
| <span id="489">489</span> |
| <span id="490">490</span> |
| <span id="491">491</span> |
| <span id="492">492</span> |
| <span id="493">493</span> |
| <span id="494">494</span> |
| <span id="495">495</span> |
| <span id="496">496</span> |
| <span id="497">497</span> |
| <span id="498">498</span> |
| <span id="499">499</span> |
| <span id="500">500</span> |
| <span id="501">501</span> |
| <span id="502">502</span> |
| <span id="503">503</span> |
| <span id="504">504</span> |
| <span id="505">505</span> |
| <span id="506">506</span> |
| <span id="507">507</span> |
| <span id="508">508</span> |
| <span id="509">509</span> |
| <span id="510">510</span> |
| <span id="511">511</span> |
| <span id="512">512</span> |
| <span id="513">513</span> |
| <span id="514">514</span> |
| <span id="515">515</span> |
| <span id="516">516</span> |
| <span id="517">517</span> |
| <span id="518">518</span> |
| <span id="519">519</span> |
| <span id="520">520</span> |
| <span id="521">521</span> |
| <span id="522">522</span> |
| <span id="523">523</span> |
| <span id="524">524</span> |
| <span id="525">525</span> |
| <span id="526">526</span> |
| <span id="527">527</span> |
| <span id="528">528</span> |
| <span id="529">529</span> |
| <span id="530">530</span> |
| <span id="531">531</span> |
| <span id="532">532</span> |
| <span id="533">533</span> |
| <span id="534">534</span> |
| <span id="535">535</span> |
| <span id="536">536</span> |
| <span id="537">537</span> |
| <span id="538">538</span> |
| <span id="539">539</span> |
| <span id="540">540</span> |
| <span id="541">541</span> |
| <span id="542">542</span> |
| <span id="543">543</span> |
| <span id="544">544</span> |
| <span id="545">545</span> |
| <span id="546">546</span> |
| <span id="547">547</span> |
| <span id="548">548</span> |
| <span id="549">549</span> |
| <span id="550">550</span> |
| <span id="551">551</span> |
| <span id="552">552</span> |
| <span id="553">553</span> |
| <span id="554">554</span> |
| <span id="555">555</span> |
| <span id="556">556</span> |
| <span id="557">557</span> |
| <span id="558">558</span> |
| <span id="559">559</span> |
| <span id="560">560</span> |
| <span id="561">561</span> |
| <span id="562">562</span> |
| <span id="563">563</span> |
| <span id="564">564</span> |
| <span id="565">565</span> |
| <span id="566">566</span> |
| <span id="567">567</span> |
| <span id="568">568</span> |
| <span id="569">569</span> |
| <span id="570">570</span> |
| <span id="571">571</span> |
| <span id="572">572</span> |
| <span id="573">573</span> |
| <span id="574">574</span> |
| <span id="575">575</span> |
| <span id="576">576</span> |
| <span id="577">577</span> |
| <span id="578">578</span> |
| <span id="579">579</span> |
| <span id="580">580</span> |
| <span id="581">581</span> |
| <span id="582">582</span> |
| <span id="583">583</span> |
| <span id="584">584</span> |
| <span id="585">585</span> |
| <span id="586">586</span> |
| <span id="587">587</span> |
| <span id="588">588</span> |
| <span id="589">589</span> |
| <span id="590">590</span> |
| <span id="591">591</span> |
| <span id="592">592</span> |
| <span id="593">593</span> |
| <span id="594">594</span> |
| <span id="595">595</span> |
| <span id="596">596</span> |
| <span id="597">597</span> |
| <span id="598">598</span> |
| <span id="599">599</span> |
| <span id="600">600</span> |
| <span id="601">601</span> |
| <span id="602">602</span> |
| <span id="603">603</span> |
| <span id="604">604</span> |
| <span id="605">605</span> |
| <span id="606">606</span> |
| <span id="607">607</span> |
| <span id="608">608</span> |
| <span id="609">609</span> |
| <span id="610">610</span> |
| <span id="611">611</span> |
| <span id="612">612</span> |
| <span id="613">613</span> |
| <span id="614">614</span> |
| <span id="615">615</span> |
| <span id="616">616</span> |
| <span id="617">617</span> |
| <span id="618">618</span> |
| <span id="619">619</span> |
| <span id="620">620</span> |
| <span id="621">621</span> |
| <span id="622">622</span> |
| <span id="623">623</span> |
| <span id="624">624</span> |
| <span id="625">625</span> |
| <span id="626">626</span> |
| <span id="627">627</span> |
| <span id="628">628</span> |
| <span id="629">629</span> |
| <span id="630">630</span> |
| <span id="631">631</span> |
| <span id="632">632</span> |
| <span id="633">633</span> |
| <span id="634">634</span> |
| <span id="635">635</span> |
| <span id="636">636</span> |
| <span id="637">637</span> |
| <span id="638">638</span> |
| <span id="639">639</span> |
| <span id="640">640</span> |
| <span id="641">641</span> |
| <span id="642">642</span> |
| <span id="643">643</span> |
| <span id="644">644</span> |
| <span id="645">645</span> |
| <span id="646">646</span> |
| <span id="647">647</span> |
| <span id="648">648</span> |
| <span id="649">649</span> |
| <span id="650">650</span> |
| <span id="651">651</span> |
| <span id="652">652</span> |
| <span id="653">653</span> |
| <span id="654">654</span> |
| <span id="655">655</span> |
| <span id="656">656</span> |
| <span id="657">657</span> |
| <span id="658">658</span> |
| <span id="659">659</span> |
| <span id="660">660</span> |
| <span id="661">661</span> |
| <span id="662">662</span> |
| <span id="663">663</span> |
| <span id="664">664</span> |
| <span id="665">665</span> |
| <span id="666">666</span> |
| <span id="667">667</span> |
| <span id="668">668</span> |
| <span id="669">669</span> |
| <span id="670">670</span> |
| <span id="671">671</span> |
| <span id="672">672</span> |
| <span id="673">673</span> |
| <span id="674">674</span> |
| <span id="675">675</span> |
| <span id="676">676</span> |
| <span id="677">677</span> |
| <span id="678">678</span> |
| <span id="679">679</span> |
| <span id="680">680</span> |
| <span id="681">681</span> |
| <span id="682">682</span> |
| <span id="683">683</span> |
| <span id="684">684</span> |
| <span id="685">685</span> |
| <span id="686">686</span> |
| <span id="687">687</span> |
| <span id="688">688</span> |
| <span id="689">689</span> |
| <span id="690">690</span> |
| <span id="691">691</span> |
| <span id="692">692</span> |
| <span id="693">693</span> |
| <span id="694">694</span> |
| <span id="695">695</span> |
| <span id="696">696</span> |
| <span id="697">697</span> |
| <span id="698">698</span> |
| <span id="699">699</span> |
| <span id="700">700</span> |
| <span id="701">701</span> |
| <span id="702">702</span> |
| <span id="703">703</span> |
| <span id="704">704</span> |
| <span id="705">705</span> |
| <span id="706">706</span> |
| <span id="707">707</span> |
| <span id="708">708</span> |
| <span id="709">709</span> |
| <span id="710">710</span> |
| <span id="711">711</span> |
| <span id="712">712</span> |
| <span id="713">713</span> |
| <span id="714">714</span> |
| <span id="715">715</span> |
| <span id="716">716</span> |
| <span id="717">717</span> |
| <span id="718">718</span> |
| <span id="719">719</span> |
| <span id="720">720</span> |
| <span id="721">721</span> |
| <span id="722">722</span> |
| <span id="723">723</span> |
| <span id="724">724</span> |
| <span id="725">725</span> |
| <span id="726">726</span> |
| <span id="727">727</span> |
| <span id="728">728</span> |
| <span id="729">729</span> |
| <span id="730">730</span> |
| <span id="731">731</span> |
| <span id="732">732</span> |
| <span id="733">733</span> |
| <span id="734">734</span> |
| <span id="735">735</span> |
| <span id="736">736</span> |
| <span id="737">737</span> |
| <span id="738">738</span> |
| <span id="739">739</span> |
| <span id="740">740</span> |
| <span id="741">741</span> |
| <span id="742">742</span> |
| <span id="743">743</span> |
| <span id="744">744</span> |
| <span id="745">745</span> |
| <span id="746">746</span> |
| <span id="747">747</span> |
| <span id="748">748</span> |
| <span id="749">749</span> |
| <span id="750">750</span> |
| <span id="751">751</span> |
| <span id="752">752</span> |
| <span id="753">753</span> |
| <span id="754">754</span> |
| <span id="755">755</span> |
| <span id="756">756</span> |
| <span id="757">757</span> |
| <span id="758">758</span> |
| <span id="759">759</span> |
| <span id="760">760</span> |
| <span id="761">761</span> |
| <span id="762">762</span> |
| <span id="763">763</span> |
| <span id="764">764</span> |
| <span id="765">765</span> |
| <span id="766">766</span> |
| <span id="767">767</span> |
| <span id="768">768</span> |
| <span id="769">769</span> |
| <span id="770">770</span> |
| <span id="771">771</span> |
| <span id="772">772</span> |
| <span id="773">773</span> |
| <span id="774">774</span> |
| <span id="775">775</span> |
| <span id="776">776</span> |
| <span id="777">777</span> |
| </pre><pre class="rust"><code><span class="kw">use </span>core::cell::UnsafeCell; |
| <span class="kw">use </span>core::default::Default; |
| <span class="kw">use </span>core::fmt; |
| <span class="kw">use </span>core::marker::PhantomData; |
| <span class="kw">use </span>core::mem; |
| <span class="kw">use </span>core::ops::{Deref, DerefMut}; |
| <span class="kw">use </span>core::ptr::NonNull; |
| <span class="kw">use </span>core::sync::atomic::{spin_loop_hint <span class="kw">as </span>cpu_relax, AtomicUsize, Ordering}; |
| |
| <span class="doccomment">/// A reader-writer lock |
| /// |
| /// This type of lock allows a number of readers or at most one writer at any |
| /// point in time. The write portion of this lock typically allows modification |
| /// of the underlying data (exclusive access) and the read portion of this lock |
| /// typically allows for read-only access (shared access). |
| /// |
| /// The type parameter `T` represents the data that this lock protects. It is |
| /// required that `T` satisfies `Send` to be shared across tasks and `Sync` to |
| /// allow concurrent access through readers. The RAII guards returned from the |
| /// locking methods implement `Deref` (and `DerefMut` for the `write` methods) |
| /// to allow access to the contained of the lock. |
| /// |
| /// An [`RwLockUpgradeableGuard`](RwLockUpgradeableGuard) can be upgraded to a |
| /// writable guard through the [`RwLockUpgradeableGuard::upgrade`](RwLockUpgradeableGuard::upgrade) |
| /// [`RwLockUpgradeableGuard::try_upgrade`](RwLockUpgradeableGuard::try_upgrade) functions. |
| /// Writable or upgradeable guards can be downgraded through their respective `downgrade` |
| /// functions. |
| /// |
| /// Based on Facebook's |
| /// [`folly/RWSpinLock.h`](https://github.com/facebook/folly/blob/a0394d84f2d5c3e50ebfd0566f9d3acb52cfab5a/folly/synchronization/RWSpinLock.h). |
| /// This implementation is unfair to writers - if the lock always has readers, then no writers will |
| /// ever get a chance. Using an upgradeable lock guard can *somewhat* alleviate this issue as no |
| /// new readers are allowed when an upgradeable guard is held, but upgradeable guards can be taken |
| /// when there are existing readers. However if the lock is that highly contended and writes are |
| /// crucial then this implementation may be a poor choice. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// use spin; |
| /// |
| /// let lock = spin::RwLock::new(5); |
| /// |
| /// // many reader locks can be held at once |
| /// { |
| /// let r1 = lock.read(); |
| /// let r2 = lock.read(); |
| /// assert_eq!(*r1, 5); |
| /// assert_eq!(*r2, 5); |
| /// } // read locks are dropped at this point |
| /// |
| /// // only one write lock may be held, however |
| /// { |
| /// let mut w = lock.write(); |
| /// *w += 1; |
| /// assert_eq!(*w, 6); |
| /// } // write lock is dropped here |
| /// ``` |
| </span><span class="kw">pub struct </span>RwLock<T: <span class="question-mark">?</span>Sized> { |
| lock: AtomicUsize, |
| data: UnsafeCell<T>, |
| } |
| |
| <span class="kw">const </span>READER: usize = <span class="number">1 </span><< <span class="number">2</span>; |
| <span class="kw">const </span>UPGRADED: usize = <span class="number">1 </span><< <span class="number">1</span>; |
| <span class="kw">const </span>WRITER: usize = <span class="number">1</span>; |
| |
| <span class="doccomment">/// A guard from which the protected data can be read |
| /// |
| /// When the guard falls out of scope it will decrement the read count, |
| /// potentially releasing the lock. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>RwLockReadGuard<<span class="lifetime">'a</span>, T: <span class="lifetime">'a </span>+ <span class="question-mark">?</span>Sized> { |
| lock: <span class="kw-2">&</span><span class="lifetime">'a </span>AtomicUsize, |
| data: NonNull<T>, |
| } |
| |
| <span class="doccomment">/// A guard to which the protected data can be written |
| /// |
| /// When the guard falls out of scope it will release the lock. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>RwLockWriteGuard<<span class="lifetime">'a</span>, T: <span class="lifetime">'a </span>+ <span class="question-mark">?</span>Sized> { |
| lock: <span class="kw-2">&</span><span class="lifetime">'a </span>AtomicUsize, |
| data: NonNull<T>, |
| <span class="attribute">#[doc(hidden)] |
| </span>_invariant: PhantomData<<span class="kw-2">&</span><span class="lifetime">'a </span><span class="kw-2">mut </span>T>, |
| } |
| |
| <span class="doccomment">/// A guard from which the protected data can be read, and can be upgraded |
| /// to a writable guard if needed |
| /// |
| /// No writers or other upgradeable guards can exist while this is in scope. New reader |
| /// creation is prevented (to alleviate writer starvation) but there may be existing readers |
| /// when the lock is acquired. |
| /// |
| /// When the guard falls out of scope it will release the lock. |
| </span><span class="attribute">#[derive(Debug)] |
| </span><span class="kw">pub struct </span>RwLockUpgradeableGuard<<span class="lifetime">'a</span>, T: <span class="lifetime">'a </span>+ <span class="question-mark">?</span>Sized> { |
| lock: <span class="kw-2">&</span><span class="lifetime">'a </span>AtomicUsize, |
| data: NonNull<T>, |
| <span class="attribute">#[doc(hidden)] |
| </span>_invariant: PhantomData<<span class="kw-2">&</span><span class="lifetime">'a </span><span class="kw-2">mut </span>T>, |
| } |
| |
| <span class="comment">// Same unsafe impls as `std::sync::RwLock` |
| </span><span class="kw">unsafe impl</span><T: <span class="question-mark">?</span>Sized + Send> Send <span class="kw">for </span>RwLock<T> {} |
| <span class="kw">unsafe impl</span><T: <span class="question-mark">?</span>Sized + Send + Sync> Sync <span class="kw">for </span>RwLock<T> {} |
| |
| <span class="kw">impl</span><T> RwLock<T> { |
| <span class="doccomment">/// Creates a new spinlock wrapping the supplied data. |
| /// |
| /// May be used statically: |
| /// |
| /// ``` |
| /// use spin; |
| /// |
| /// static RW_LOCK: spin::RwLock<()> = spin::RwLock::new(()); |
| /// |
| /// fn demo() { |
| /// let lock = RW_LOCK.read(); |
| /// // do something with lock |
| /// drop(lock); |
| /// } |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub const fn </span>new(user_data: T) -> RwLock<T> { |
| RwLock { |
| lock: AtomicUsize::new(<span class="number">0</span>), |
| data: UnsafeCell::new(user_data), |
| } |
| } |
| |
| <span class="doccomment">/// Consumes this `RwLock`, returning the underlying data. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>into_inner(<span class="self">self</span>) -> T { |
| <span class="comment">// We know statically that there are no outstanding references to |
| // `self` so there's no need to lock. |
| </span><span class="kw">let </span>RwLock { data, .. } = <span class="self">self</span>; |
| data.into_inner() |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized> RwLock<T> { |
| <span class="doccomment">/// Locks this rwlock with shared read access, blocking the current thread |
| /// until it can be acquired. |
| /// |
| /// The calling thread will be blocked until there are no more writers which |
| /// hold the lock. There may be other readers currently inside the lock when |
| /// this method returns. This method does not provide any guarantees with |
| /// respect to the ordering of whether contentious readers or writers will |
| /// acquire the lock first. |
| /// |
| /// Returns an RAII guard which will release this thread's shared access |
| /// once it is dropped. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// { |
| /// let mut data = mylock.read(); |
| /// // The lock is now locked and the data can be read |
| /// println!("{}", *data); |
| /// // The lock is dropped |
| /// } |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>read(<span class="kw-2">&</span><span class="self">self</span>) -> RwLockReadGuard<T> { |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="self">self</span>.try_read() { |
| <span class="prelude-val">Some</span>(guard) => <span class="kw">return </span>guard, |
| <span class="prelude-val">None </span>=> cpu_relax(), |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Attempt to acquire this lock with shared read access. |
| /// |
| /// This function will never block and will return immediately if `read` |
| /// would otherwise succeed. Returns `Some` of an RAII guard which will |
| /// release the shared access of this thread when dropped, or `None` if the |
| /// access could not be granted. This method does not provide any |
| /// guarantees with respect to the ordering of whether contentious readers |
| /// or writers will acquire the lock first. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// { |
| /// match mylock.try_read() { |
| /// Some(data) => { |
| /// // The lock is now locked and the data can be read |
| /// println!("{}", *data); |
| /// // The lock is dropped |
| /// }, |
| /// None => (), // no cigar |
| /// }; |
| /// } |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>try_read(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><RwLockReadGuard<T>> { |
| <span class="kw">let </span>value = <span class="self">self</span>.lock.fetch_add(READER, Ordering::Acquire); |
| |
| <span class="comment">// We check the UPGRADED bit here so that new readers are prevented when an UPGRADED lock is held. |
| // This helps reduce writer starvation. |
| </span><span class="kw">if </span>value & (WRITER | UPGRADED) != <span class="number">0 </span>{ |
| <span class="comment">// Lock is taken, undo. |
| </span><span class="self">self</span>.lock.fetch_sub(READER, Ordering::Release); |
| <span class="prelude-val">None |
| </span>} <span class="kw">else </span>{ |
| <span class="prelude-val">Some</span>(RwLockReadGuard { |
| lock: <span class="kw-2">&</span><span class="self">self</span>.lock, |
| data: <span class="kw">unsafe </span>{ NonNull::new_unchecked(<span class="self">self</span>.data.get()) }, |
| }) |
| } |
| } |
| |
| <span class="doccomment">/// Force decrement the reader count. |
| /// |
| /// This is *extremely* unsafe if there are outstanding `RwLockReadGuard`s |
| /// live, or if called more times than `read` has been called, but can be |
| /// useful in FFI contexts where the caller doesn't know how to deal with |
| /// RAII. The underlying atomic operation uses `Ordering::Release`. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub unsafe fn </span>force_read_decrement(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="macro">debug_assert!</span>(<span class="self">self</span>.lock.load(Ordering::Relaxed) & !WRITER > <span class="number">0</span>); |
| <span class="self">self</span>.lock.fetch_sub(READER, Ordering::Release); |
| } |
| |
| <span class="doccomment">/// Force unlock exclusive write access. |
| /// |
| /// This is *extremely* unsafe if there are outstanding `RwLockWriteGuard`s |
| /// live, or if called when there are current readers, but can be useful in |
| /// FFI contexts where the caller doesn't know how to deal with RAII. The |
| /// underlying atomic operation uses `Ordering::Release`. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub unsafe fn </span>force_write_unlock(<span class="kw-2">&</span><span class="self">self</span>) { |
| <span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED), <span class="number">0</span>); |
| <span class="self">self</span>.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release); |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>try_write_internal(<span class="kw-2">&</span><span class="self">self</span>, strong: bool) -> <span class="prelude-ty">Option</span><RwLockWriteGuard<T>> { |
| <span class="kw">if </span>compare_exchange( |
| <span class="kw-2">&</span><span class="self">self</span>.lock, |
| <span class="number">0</span>, |
| WRITER, |
| Ordering::Acquire, |
| Ordering::Relaxed, |
| strong, |
| ) |
| .is_ok() |
| { |
| <span class="prelude-val">Some</span>(RwLockWriteGuard { |
| lock: <span class="kw-2">&</span><span class="self">self</span>.lock, |
| data: <span class="kw">unsafe </span>{ NonNull::new_unchecked(<span class="self">self</span>.data.get()) }, |
| _invariant: PhantomData, |
| }) |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">None |
| </span>} |
| } |
| |
| <span class="doccomment">/// Lock this rwlock with exclusive write access, blocking the current |
| /// thread until it can be acquired. |
| /// |
| /// This function will not return while other writers or other readers |
| /// currently have access to the lock. |
| /// |
| /// Returns an RAII guard which will drop the write access of this rwlock |
| /// when dropped. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// { |
| /// let mut data = mylock.write(); |
| /// // The lock is now locked and the data can be written |
| /// *data += 1; |
| /// // The lock is dropped |
| /// } |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>write(<span class="kw-2">&</span><span class="self">self</span>) -> RwLockWriteGuard<T> { |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="self">self</span>.try_write_internal(<span class="bool-val">false</span>) { |
| <span class="prelude-val">Some</span>(guard) => <span class="kw">return </span>guard, |
| <span class="prelude-val">None </span>=> cpu_relax(), |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Attempt to lock this rwlock with exclusive write access. |
| /// |
| /// This function does not ever block, and it will return `None` if a call |
| /// to `write` would otherwise block. If successful, an RAII guard is |
| /// returned. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// { |
| /// match mylock.try_write() { |
| /// Some(mut data) => { |
| /// // The lock is now locked and the data can be written |
| /// *data += 1; |
| /// // The lock is implicitly dropped |
| /// }, |
| /// None => (), // no cigar |
| /// }; |
| /// } |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>try_write(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><RwLockWriteGuard<T>> { |
| <span class="self">self</span>.try_write_internal(<span class="bool-val">true</span>) |
| } |
| |
| <span class="doccomment">/// Obtain a readable lock guard that can later be upgraded to a writable lock guard. |
| /// Upgrades can be done through the [`RwLockUpgradeableGuard::upgrade`](RwLockUpgradeableGuard::upgrade) method. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>upgradeable_read(<span class="kw-2">&</span><span class="self">self</span>) -> RwLockUpgradeableGuard<T> { |
| <span class="kw">loop </span>{ |
| <span class="kw">match </span><span class="self">self</span>.try_upgradeable_read() { |
| <span class="prelude-val">Some</span>(guard) => <span class="kw">return </span>guard, |
| <span class="prelude-val">None </span>=> cpu_relax(), |
| } |
| } |
| } |
| |
| <span class="doccomment">/// Tries to obtain an upgradeable lock guard. |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>try_upgradeable_read(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="prelude-ty">Option</span><RwLockUpgradeableGuard<T>> { |
| <span class="kw">if </span><span class="self">self</span>.lock.fetch_or(UPGRADED, Ordering::Acquire) & (WRITER | UPGRADED) == <span class="number">0 </span>{ |
| <span class="prelude-val">Some</span>(RwLockUpgradeableGuard { |
| lock: <span class="kw-2">&</span><span class="self">self</span>.lock, |
| data: <span class="kw">unsafe </span>{ NonNull::new_unchecked(<span class="self">self</span>.data.get()) }, |
| _invariant: PhantomData, |
| }) |
| } <span class="kw">else </span>{ |
| <span class="comment">// We can't unflip the UPGRADED bit back just yet as there is another upgradeable or write lock. |
| // When they unlock, they will clear the bit. |
| </span><span class="prelude-val">None |
| </span>} |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + fmt::Debug> fmt::Debug <span class="kw">for </span>RwLock<T> { |
| <span class="kw">fn </span>fmt(<span class="kw-2">&</span><span class="self">self</span>, f: <span class="kw-2">&mut </span>fmt::Formatter) -> fmt::Result { |
| <span class="kw">match </span><span class="self">self</span>.try_read() { |
| <span class="prelude-val">Some</span>(guard) => <span class="macro">write!</span>(f, <span class="string">"RwLock {{ data: "</span>) |
| .and_then(|()| (<span class="kw-2">&*</span>guard).fmt(f)) |
| .and_then(|()| <span class="macro">write!</span>(f, <span class="string">"}}"</span>)), |
| <span class="prelude-val">None </span>=> <span class="macro">write!</span>(f, <span class="string">"RwLock {{ <locked> }}"</span>), |
| } |
| } |
| } |
| |
| <span class="kw">impl</span><T: <span class="question-mark">?</span>Sized + Default> Default <span class="kw">for </span>RwLock<T> { |
| <span class="kw">fn </span>default() -> RwLock<T> { |
| RwLock::new(Default::default()) |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> RwLockUpgradeableGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>try_upgrade_internal(<span class="self">self</span>, strong: bool) -> <span class="prelude-ty">Result</span><RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T>, <span class="self">Self</span>> { |
| <span class="kw">if </span>compare_exchange( |
| <span class="kw-2">&</span><span class="self">self</span>.lock, |
| UPGRADED, |
| WRITER, |
| Ordering::Acquire, |
| Ordering::Relaxed, |
| strong, |
| ) |
| .is_ok() |
| { |
| <span class="comment">// Upgrade successful |
| </span><span class="kw">let </span>out = <span class="prelude-val">Ok</span>(RwLockWriteGuard { |
| lock: <span class="kw-2">&</span><span class="self">self</span>.lock, |
| data: <span class="self">self</span>.data, |
| _invariant: PhantomData, |
| }); |
| |
| <span class="comment">// Forget the old guard so its destructor doesn't run |
| </span>mem::forget(<span class="self">self</span>); |
| |
| out |
| } <span class="kw">else </span>{ |
| <span class="prelude-val">Err</span>(<span class="self">self</span>) |
| } |
| } |
| |
| <span class="doccomment">/// Upgrades an upgradeable lock guard to a writable lock guard. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// |
| /// let upgradeable = mylock.upgradeable_read(); // Readable, but not yet writable |
| /// let writable = upgradeable.upgrade(); |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>upgrade(<span class="kw-2">mut </span><span class="self">self</span>) -> RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">loop </span>{ |
| <span class="self">self </span>= <span class="kw">match </span><span class="self">self</span>.try_upgrade_internal(<span class="bool-val">false</span>) { |
| <span class="prelude-val">Ok</span>(guard) => <span class="kw">return </span>guard, |
| <span class="prelude-val">Err</span>(e) => e, |
| }; |
| |
| cpu_relax(); |
| } |
| } |
| |
| <span class="doccomment">/// Tries to upgrade an upgradeable lock guard to a writable lock guard. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// let upgradeable = mylock.upgradeable_read(); // Readable, but not yet writable |
| /// |
| /// match upgradeable.try_upgrade() { |
| /// Ok(writable) => /* upgrade successful - use writable lock guard */ (), |
| /// Err(upgradeable) => /* upgrade unsuccessful */ (), |
| /// }; |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>try_upgrade(<span class="self">self</span>) -> <span class="prelude-ty">Result</span><RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T>, <span class="self">Self</span>> { |
| <span class="self">self</span>.try_upgrade_internal(<span class="bool-val">true</span>) |
| } |
| |
| <span class="attribute">#[inline] |
| </span><span class="doccomment">/// Downgrades the upgradeable lock guard to a readable, shared lock guard. Cannot fail and is guaranteed not to spin. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(1); |
| /// |
| /// let upgradeable = mylock.upgradeable_read(); |
| /// assert!(mylock.try_read().is_none()); |
| /// assert_eq!(*upgradeable, 1); |
| /// |
| /// let readable = upgradeable.downgrade(); // This is guaranteed not to spin |
| /// assert!(mylock.try_read().is_some()); |
| /// assert_eq!(*readable, 1); |
| /// ``` |
| </span><span class="kw">pub fn </span>downgrade(<span class="self">self</span>) -> RwLockReadGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="comment">// Reserve the read guard for ourselves |
| </span><span class="self">self</span>.lock.fetch_add(READER, Ordering::Acquire); |
| |
| RwLockReadGuard { |
| lock: <span class="kw-2">&</span><span class="self">self</span>.lock, |
| data: <span class="self">self</span>.data, |
| } |
| |
| <span class="comment">// Dropping self removes the UPGRADED bit |
| </span>} |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="doccomment">/// Downgrades the writable lock guard to a readable, shared lock guard. Cannot fail and is guaranteed not to spin. |
| /// |
| /// ``` |
| /// let mylock = spin::RwLock::new(0); |
| /// |
| /// let mut writable = mylock.write(); |
| /// *writable = 1; |
| /// |
| /// let readable = writable.downgrade(); // This is guaranteed not to spin |
| /// # let readable_2 = mylock.try_read().unwrap(); |
| /// assert_eq!(*readable, 1); |
| /// ``` |
| </span><span class="attribute">#[inline] |
| </span><span class="kw">pub fn </span>downgrade(<span class="self">self</span>) -> RwLockReadGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="comment">// Reserve the read guard for ourselves |
| </span><span class="self">self</span>.lock.fetch_add(READER, Ordering::Acquire); |
| |
| RwLockReadGuard { |
| lock: <span class="kw-2">&</span><span class="self">self</span>.lock, |
| data: <span class="self">self</span>.data, |
| } |
| |
| <span class="comment">// Dropping self removes the WRITER bit |
| </span>} |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> Deref <span class="kw">for </span>RwLockReadGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">type </span>Target = T; |
| |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.data.as_ref() } |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> Deref <span class="kw">for </span>RwLockUpgradeableGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">type </span>Target = T; |
| |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.data.as_ref() } |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> Deref <span class="kw">for </span>RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">type </span>Target = T; |
| |
| <span class="kw">fn </span>deref(<span class="kw-2">&</span><span class="self">self</span>) -> <span class="kw-2">&</span>T { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.data.as_ref() } |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> DerefMut <span class="kw">for </span>RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">fn </span>deref_mut(<span class="kw-2">&mut </span><span class="self">self</span>) -> <span class="kw-2">&mut </span>T { |
| <span class="kw">unsafe </span>{ <span class="self">self</span>.data.as_mut() } |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> Drop <span class="kw">for </span>RwLockReadGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="macro">debug_assert!</span>(<span class="self">self</span>.lock.load(Ordering::Relaxed) & !(WRITER | UPGRADED) > <span class="number">0</span>); |
| <span class="self">self</span>.lock.fetch_sub(READER, Ordering::Release); |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> Drop <span class="kw">for </span>RwLockUpgradeableGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="macro">debug_assert_eq!</span>( |
| <span class="self">self</span>.lock.load(Ordering::Relaxed) & (WRITER | UPGRADED), |
| UPGRADED |
| ); |
| <span class="self">self</span>.lock.fetch_sub(UPGRADED, Ordering::AcqRel); |
| } |
| } |
| |
| <span class="kw">impl</span><<span class="lifetime">'rwlock</span>, T: <span class="question-mark">?</span>Sized> Drop <span class="kw">for </span>RwLockWriteGuard<<span class="lifetime">'rwlock</span>, T> { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="macro">debug_assert_eq!</span>(<span class="self">self</span>.lock.load(Ordering::Relaxed) & WRITER, WRITER); |
| |
| <span class="comment">// Writer is responsible for clearing both WRITER and UPGRADED bits. |
| // The UPGRADED bit may be set if an upgradeable lock attempts an upgrade while this lock is held. |
| </span><span class="self">self</span>.lock.fetch_and(!(WRITER | UPGRADED), Ordering::Release); |
| } |
| } |
| |
| <span class="attribute">#[inline(always)] |
| </span><span class="kw">fn </span>compare_exchange( |
| atomic: <span class="kw-2">&</span>AtomicUsize, |
| current: usize, |
| new: usize, |
| success: Ordering, |
| failure: Ordering, |
| strong: bool, |
| ) -> <span class="prelude-ty">Result</span><usize, usize> { |
| <span class="kw">if </span>strong { |
| atomic.compare_exchange(current, new, success, failure) |
| } <span class="kw">else </span>{ |
| atomic.compare_exchange_weak(current, new, success, failure) |
| } |
| } |
| |
| <span class="attribute">#[cfg(test)] |
| </span><span class="kw">mod </span>tests { |
| <span class="kw">use </span>std::prelude::v1::<span class="kw-2">*</span>; |
| |
| <span class="kw">use </span>std::sync::atomic::{AtomicUsize, Ordering}; |
| <span class="kw">use </span>std::sync::mpsc::channel; |
| <span class="kw">use </span>std::sync::Arc; |
| <span class="kw">use </span>std::thread; |
| |
| <span class="kw">use super</span>::<span class="kw-2">*</span>; |
| |
| <span class="attribute">#[derive(Eq, PartialEq, Debug)] |
| </span><span class="kw">struct </span>NonCopy(i32); |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>smoke() { |
| <span class="kw">let </span>l = RwLock::new(()); |
| drop(l.read()); |
| drop(l.write()); |
| drop((l.read(), l.read())); |
| drop(l.write()); |
| } |
| |
| <span class="comment">// TODO: needs RNG |
| //#[test] |
| //fn frob() { |
| // static R: RwLock = RwLock::new(); |
| // const N: usize = 10; |
| // const M: usize = 1000; |
| // |
| // let (tx, rx) = channel::<()>(); |
| // for _ in 0..N { |
| // let tx = tx.clone(); |
| // thread::spawn(move|| { |
| // let mut rng = rand::thread_rng(); |
| // for _ in 0..M { |
| // if rng.gen_weighted_bool(N) { |
| // drop(R.write()); |
| // } else { |
| // drop(R.read()); |
| // } |
| // } |
| // drop(tx); |
| // }); |
| // } |
| // drop(tx); |
| // let _ = rx.recv(); |
| // unsafe { R.destroy(); } |
| //} |
| |
| </span><span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_rw_arc() { |
| <span class="kw">let </span>arc = Arc::new(RwLock::new(<span class="number">0</span>)); |
| <span class="kw">let </span>arc2 = arc.clone(); |
| <span class="kw">let </span>(tx, rx) = channel(); |
| |
| thread::spawn(<span class="kw">move </span>|| { |
| <span class="kw">let </span><span class="kw-2">mut </span>lock = arc2.write(); |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">10 </span>{ |
| <span class="kw">let </span>tmp = <span class="kw-2">*</span>lock; |
| <span class="kw-2">*</span>lock = -<span class="number">1</span>; |
| thread::yield_now(); |
| <span class="kw-2">*</span>lock = tmp + <span class="number">1</span>; |
| } |
| tx.send(()).unwrap(); |
| }); |
| |
| <span class="comment">// Readers try to catch the writer in the act |
| </span><span class="kw">let </span><span class="kw-2">mut </span>children = Vec::new(); |
| <span class="kw">for _ in </span><span class="number">0</span>..<span class="number">5 </span>{ |
| <span class="kw">let </span>arc3 = arc.clone(); |
| children.push(thread::spawn(<span class="kw">move </span>|| { |
| <span class="kw">let </span>lock = arc3.read(); |
| <span class="macro">assert!</span>(<span class="kw-2">*</span>lock >= <span class="number">0</span>); |
| })); |
| } |
| |
| <span class="comment">// Wait for children to pass their asserts |
| </span><span class="kw">for </span>r <span class="kw">in </span>children { |
| <span class="macro">assert!</span>(r.join().is_ok()); |
| } |
| |
| <span class="comment">// Wait for writer to finish |
| </span>rx.recv().unwrap(); |
| <span class="kw">let </span>lock = arc.read(); |
| <span class="macro">assert_eq!</span>(<span class="kw-2">*</span>lock, <span class="number">10</span>); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_rw_access_in_unwind() { |
| <span class="kw">let </span>arc = Arc::new(RwLock::new(<span class="number">1</span>)); |
| <span class="kw">let </span>arc2 = arc.clone(); |
| <span class="kw">let _ </span>= thread::spawn(<span class="kw">move </span>|| -> () { |
| <span class="kw">struct </span>Unwinder { |
| i: Arc<RwLock<isize>>, |
| } |
| <span class="kw">impl </span>Drop <span class="kw">for </span>Unwinder { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="kw">let </span><span class="kw-2">mut </span>lock = <span class="self">self</span>.i.write(); |
| <span class="kw-2">*</span>lock += <span class="number">1</span>; |
| } |
| } |
| <span class="kw">let </span>_u = Unwinder { i: arc2 }; |
| <span class="macro">panic!</span>(); |
| }) |
| .join(); |
| <span class="kw">let </span>lock = arc.read(); |
| <span class="macro">assert_eq!</span>(<span class="kw-2">*</span>lock, <span class="number">2</span>); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_rwlock_unsized() { |
| <span class="kw">let </span>rw: <span class="kw-2">&</span>RwLock<[i32]> = <span class="kw-2">&</span>RwLock::new([<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>]); |
| { |
| <span class="kw">let </span>b = <span class="kw-2">&mut *</span>rw.write(); |
| b[<span class="number">0</span>] = <span class="number">4</span>; |
| b[<span class="number">2</span>] = <span class="number">5</span>; |
| } |
| <span class="kw">let </span>comp: <span class="kw-2">&</span>[i32] = <span class="kw-2">&</span>[<span class="number">4</span>, <span class="number">2</span>, <span class="number">5</span>]; |
| <span class="macro">assert_eq!</span>(<span class="kw-2">&*</span>rw.read(), comp); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_rwlock_try_write() { |
| <span class="kw">use </span>std::mem::drop; |
| |
| <span class="kw">let </span>lock = RwLock::new(<span class="number">0isize</span>); |
| <span class="kw">let </span>read_guard = lock.read(); |
| |
| <span class="kw">let </span>write_result = lock.try_write(); |
| <span class="kw">match </span>write_result { |
| <span class="prelude-val">None </span>=> (), |
| <span class="prelude-val">Some</span>(<span class="kw">_</span>) => <span class="macro">assert!</span>( |
| <span class="bool-val">false</span>, |
| <span class="string">"try_write should not succeed while read_guard is in scope" |
| </span>), |
| } |
| |
| drop(read_guard); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_rw_try_read() { |
| <span class="kw">let </span>m = RwLock::new(<span class="number">0</span>); |
| mem::forget(m.write()); |
| <span class="macro">assert!</span>(m.try_read().is_none()); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_into_inner() { |
| <span class="kw">let </span>m = RwLock::new(NonCopy(<span class="number">10</span>)); |
| <span class="macro">assert_eq!</span>(m.into_inner(), NonCopy(<span class="number">10</span>)); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_into_inner_drop() { |
| <span class="kw">struct </span>Foo(Arc<AtomicUsize>); |
| <span class="kw">impl </span>Drop <span class="kw">for </span>Foo { |
| <span class="kw">fn </span>drop(<span class="kw-2">&mut </span><span class="self">self</span>) { |
| <span class="self">self</span>.<span class="number">0</span>.fetch_add(<span class="number">1</span>, Ordering::SeqCst); |
| } |
| } |
| <span class="kw">let </span>num_drops = Arc::new(AtomicUsize::new(<span class="number">0</span>)); |
| <span class="kw">let </span>m = RwLock::new(Foo(num_drops.clone())); |
| <span class="macro">assert_eq!</span>(num_drops.load(Ordering::SeqCst), <span class="number">0</span>); |
| { |
| <span class="kw">let </span>_inner = m.into_inner(); |
| <span class="macro">assert_eq!</span>(num_drops.load(Ordering::SeqCst), <span class="number">0</span>); |
| } |
| <span class="macro">assert_eq!</span>(num_drops.load(Ordering::SeqCst), <span class="number">1</span>); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_force_read_decrement() { |
| <span class="kw">let </span>m = RwLock::new(()); |
| ::std::mem::forget(m.read()); |
| ::std::mem::forget(m.read()); |
| ::std::mem::forget(m.read()); |
| <span class="macro">assert!</span>(m.try_write().is_none()); |
| <span class="kw">unsafe </span>{ |
| m.force_read_decrement(); |
| m.force_read_decrement(); |
| } |
| <span class="macro">assert!</span>(m.try_write().is_none()); |
| <span class="kw">unsafe </span>{ |
| m.force_read_decrement(); |
| } |
| <span class="macro">assert!</span>(m.try_write().is_some()); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_force_write_unlock() { |
| <span class="kw">let </span>m = RwLock::new(()); |
| ::std::mem::forget(m.write()); |
| <span class="macro">assert!</span>(m.try_read().is_none()); |
| <span class="kw">unsafe </span>{ |
| m.force_write_unlock(); |
| } |
| <span class="macro">assert!</span>(m.try_read().is_some()); |
| } |
| |
| <span class="attribute">#[test] |
| </span><span class="kw">fn </span>test_upgrade_downgrade() { |
| <span class="kw">let </span>m = RwLock::new(()); |
| { |
| <span class="kw">let </span>_r = m.read(); |
| <span class="kw">let </span>upg = m.try_upgradeable_read().unwrap(); |
| <span class="macro">assert!</span>(m.try_read().is_none()); |
| <span class="macro">assert!</span>(m.try_write().is_none()); |
| <span class="macro">assert!</span>(upg.try_upgrade().is_err()); |
| } |
| { |
| <span class="kw">let </span>w = m.write(); |
| <span class="macro">assert!</span>(m.try_upgradeable_read().is_none()); |
| <span class="kw">let </span>_r = w.downgrade(); |
| <span class="macro">assert!</span>(m.try_upgradeable_read().is_some()); |
| <span class="macro">assert!</span>(m.try_read().is_some()); |
| <span class="macro">assert!</span>(m.try_write().is_none()); |
| } |
| { |
| <span class="kw">let </span>_u = m.upgradeable_read(); |
| <span class="macro">assert!</span>(m.try_upgradeable_read().is_none()); |
| } |
| |
| <span class="macro">assert!</span>(m.try_upgradeable_read().unwrap().try_upgrade().is_ok()); |
| } |
| } |
| </code></pre></div> |
| </section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="spin" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
