Google Git
Sign in
apache / incubator-teaclave-website / refs/heads/asf-site / . / api-docs / crates-enclave / src / crossbeam_epoch / guard.rs.html
blob: b6e33f235b819e6f2cb0f804c7dba38924024b25 [file] [log] [blame]
<!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="Source of the Rust file `/root/.cargo/registry/src/github.com-1ecc6299db9ec823/crossbeam-epoch-0.9.14/src/guard.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>guard.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="../../crossbeam_epoch/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="../../crossbeam_epoch/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>
</pre><pre class="rust"><code><span class="kw">use </span>core::fmt;
<span class="kw">use </span>core::mem;
<span class="kw">use </span>scopeguard::defer;
<span class="kw">use </span><span class="kw">crate</span>::atomic::Shared;
<span class="kw">use </span><span class="kw">crate</span>::collector::Collector;
<span class="kw">use </span><span class="kw">crate</span>::deferred::Deferred;
<span class="kw">use </span><span class="kw">crate</span>::internal::Local;
<span class="doccomment">/// A guard that keeps the current thread pinned.
///
/// # Pinning
///
/// The current thread is pinned by calling [`pin`], which returns a new guard:
///
/// ```
/// use crossbeam_epoch as epoch;
///
/// // It is often convenient to prefix a call to `pin` with a `&amp;` in order to create a reference.
/// // This is not really necessary, but makes passing references to the guard a bit easier.
/// let guard = &amp;epoch::pin();
/// ```
///
/// When a guard gets dropped, the current thread is automatically unpinned.
///
/// # Pointers on the stack
///
/// Having a guard allows us to create pointers on the stack to heap-allocated objects.
/// For example:
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic};
/// use std::sync::atomic::Ordering::SeqCst;
///
/// // Create a heap-allocated number.
/// let a = Atomic::new(777);
///
/// // Pin the current thread.
/// let guard = &amp;epoch::pin();
///
/// // Load the heap-allocated object and create pointer `p` on the stack.
/// let p = a.load(SeqCst, guard);
///
/// // Dereference the pointer and print the value:
/// if let Some(num) = unsafe { p.as_ref() } {
/// println!(&quot;The number is {}.&quot;, num);
/// }
/// # unsafe { drop(a.into_owned()); } // avoid leak
/// ```
///
/// # Multiple guards
///
/// Pinning is reentrant and it is perfectly legal to create multiple guards. In that case, the
/// thread will actually be pinned only when the first guard is created and unpinned when the last
/// one is dropped:
///
/// ```
/// use crossbeam_epoch as epoch;
///
/// let guard1 = epoch::pin();
/// let guard2 = epoch::pin();
/// assert!(epoch::is_pinned());
/// drop(guard1);
/// assert!(epoch::is_pinned());
/// drop(guard2);
/// assert!(!epoch::is_pinned());
/// ```
///
/// [`pin`]: super::pin
</span><span class="kw">pub struct </span>Guard {
<span class="kw">pub</span>(<span class="kw">crate</span>) local: <span class="kw-2">*const </span>Local,
}
<span class="kw">impl </span>Guard {
<span class="doccomment">/// Stores a function so that it can be executed at some point after all currently pinned
/// threads get unpinned.
///
/// This method first stores `f` into the thread-local (or handle-local) cache. If this cache
/// becomes full, some functions are moved into the global cache. At the same time, some
/// functions from both local and global caches may get executed in order to incrementally
/// clean up the caches as they fill up.
///
/// There is no guarantee when exactly `f` will be executed. The only guarantee is that it
/// won&#39;t be executed until all currently pinned threads get unpinned. In theory, `f` might
/// never run, but the epoch-based garbage collection will make an effort to execute it
/// reasonably soon.
///
/// If this method is called from an [`unprotected`] guard, the function will simply be
/// executed immediately.
</span><span class="kw">pub fn </span>defer&lt;F, R&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, f: F)
<span class="kw">where
</span>F: FnOnce() -&gt; R,
F: Send + <span class="lifetime">&#39;static</span>,
{
<span class="kw">unsafe </span>{
<span class="self">self</span>.defer_unchecked(f);
}
}
<span class="doccomment">/// Stores a function so that it can be executed at some point after all currently pinned
/// threads get unpinned.
///
/// This method first stores `f` into the thread-local (or handle-local) cache. If this cache
/// becomes full, some functions are moved into the global cache. At the same time, some
/// functions from both local and global caches may get executed in order to incrementally
/// clean up the caches as they fill up.
///
/// There is no guarantee when exactly `f` will be executed. The only guarantee is that it
/// won&#39;t be executed until all currently pinned threads get unpinned. In theory, `f` might
/// never run, but the epoch-based garbage collection will make an effort to execute it
/// reasonably soon.
///
/// If this method is called from an [`unprotected`] guard, the function will simply be
/// executed immediately.
///
/// # Safety
///
/// The given function must not hold reference onto the stack. It is highly recommended that
/// the passed function is **always** marked with `move` in order to prevent accidental
/// borrows.
///
/// ```
/// use crossbeam_epoch as epoch;
///
/// let guard = &amp;epoch::pin();
/// let message = &quot;Hello!&quot;;
/// unsafe {
/// // ALWAYS use `move` when sending a closure into `defer_unchecked`.
/// guard.defer_unchecked(move || {
/// println!(&quot;{}&quot;, message);
/// });
/// }
/// ```
///
/// Apart from that, keep in mind that another thread may execute `f`, so anything accessed by
/// the closure must be `Send`.
///
/// We intentionally didn&#39;t require `F: Send`, because Rust&#39;s type systems usually cannot prove
/// `F: Send` for typical use cases. For example, consider the following code snippet, which
/// exemplifies the typical use case of deferring the deallocation of a shared reference:
///
/// ```ignore
/// let shared = Owned::new(7i32).into_shared(guard);
/// guard.defer_unchecked(move || shared.into_owned()); // `Shared` is not `Send`!
/// ```
///
/// While `Shared` is not `Send`, it&#39;s safe for another thread to call the deferred function,
/// because it&#39;s called only after the grace period and `shared` is no longer shared with other
/// threads. But we don&#39;t expect type systems to prove this.
///
/// # Examples
///
/// When a heap-allocated object in a data structure becomes unreachable, it has to be
/// deallocated. However, the current thread and other threads may be still holding references
/// on the stack to that same object. Therefore it cannot be deallocated before those references
/// get dropped. This method can defer deallocation until all those threads get unpinned and
/// consequently drop all their references on the stack.
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic, Owned};
/// use std::sync::atomic::Ordering::SeqCst;
///
/// let a = Atomic::new(&quot;foo&quot;);
///
/// // Now suppose that `a` is shared among multiple threads and concurrently
/// // accessed and modified...
///
/// // Pin the current thread.
/// let guard = &amp;epoch::pin();
///
/// // Steal the object currently stored in `a` and swap it with another one.
/// let p = a.swap(Owned::new(&quot;bar&quot;).into_shared(guard), SeqCst, guard);
///
/// if !p.is_null() {
/// // The object `p` is pointing to is now unreachable.
/// // Defer its deallocation until all currently pinned threads get unpinned.
/// unsafe {
/// // ALWAYS use `move` when sending a closure into `defer_unchecked`.
/// guard.defer_unchecked(move || {
/// println!(&quot;{} is now being deallocated.&quot;, p.deref());
/// // Now we have unique access to the object pointed to by `p` and can turn it
/// // into an `Owned`. Dropping the `Owned` will deallocate the object.
/// drop(p.into_owned());
/// });
/// }
/// }
/// # unsafe { drop(a.into_owned()); } // avoid leak
/// ```
</span><span class="kw">pub unsafe fn </span>defer_unchecked&lt;F, R&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, f: F)
<span class="kw">where
</span>F: FnOnce() -&gt; R,
{
<span class="kw">if let </span><span class="prelude-val">Some</span>(local) = <span class="self">self</span>.local.as_ref() {
local.defer(Deferred::new(<span class="kw">move </span>|| drop(f())), <span class="self">self</span>);
} <span class="kw">else </span>{
drop(f());
}
}
<span class="doccomment">/// Stores a destructor for an object so that it can be deallocated and dropped at some point
/// after all currently pinned threads get unpinned.
///
/// This method first stores the destructor into the thread-local (or handle-local) cache. If
/// this cache becomes full, some destructors are moved into the global cache. At the same
/// time, some destructors from both local and global caches may get executed in order to
/// incrementally clean up the caches as they fill up.
///
/// There is no guarantee when exactly the destructor will be executed. The only guarantee is
/// that it won&#39;t be executed until all currently pinned threads get unpinned. In theory, the
/// destructor might never run, but the epoch-based garbage collection will make an effort to
/// execute it reasonably soon.
///
/// If this method is called from an [`unprotected`] guard, the destructor will simply be
/// executed immediately.
///
/// # Safety
///
/// The object must not be reachable by other threads anymore, otherwise it might be still in
/// use when the destructor runs.
///
/// Apart from that, keep in mind that another thread may execute the destructor, so the object
/// must be sendable to other threads.
///
/// We intentionally didn&#39;t require `T: Send`, because Rust&#39;s type systems usually cannot prove
/// `T: Send` for typical use cases. For example, consider the following code snippet, which
/// exemplifies the typical use case of deferring the deallocation of a shared reference:
///
/// ```ignore
/// let shared = Owned::new(7i32).into_shared(guard);
/// guard.defer_destroy(shared); // `Shared` is not `Send`!
/// ```
///
/// While `Shared` is not `Send`, it&#39;s safe for another thread to call the destructor, because
/// it&#39;s called only after the grace period and `shared` is no longer shared with other
/// threads. But we don&#39;t expect type systems to prove this.
///
/// # Examples
///
/// When a heap-allocated object in a data structure becomes unreachable, it has to be
/// deallocated. However, the current thread and other threads may be still holding references
/// on the stack to that same object. Therefore it cannot be deallocated before those references
/// get dropped. This method can defer deallocation until all those threads get unpinned and
/// consequently drop all their references on the stack.
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic, Owned};
/// use std::sync::atomic::Ordering::SeqCst;
///
/// let a = Atomic::new(&quot;foo&quot;);
///
/// // Now suppose that `a` is shared among multiple threads and concurrently
/// // accessed and modified...
///
/// // Pin the current thread.
/// let guard = &amp;epoch::pin();
///
/// // Steal the object currently stored in `a` and swap it with another one.
/// let p = a.swap(Owned::new(&quot;bar&quot;).into_shared(guard), SeqCst, guard);
///
/// if !p.is_null() {
/// // The object `p` is pointing to is now unreachable.
/// // Defer its deallocation until all currently pinned threads get unpinned.
/// unsafe {
/// guard.defer_destroy(p);
/// }
/// }
/// # unsafe { drop(a.into_owned()); } // avoid leak
/// ```
</span><span class="kw">pub unsafe fn </span>defer_destroy&lt;T&gt;(<span class="kw-2">&amp;</span><span class="self">self</span>, ptr: Shared&lt;<span class="lifetime">&#39;_</span>, T&gt;) {
<span class="self">self</span>.defer_unchecked(<span class="kw">move </span>|| ptr.into_owned());
}
<span class="doccomment">/// Clears up the thread-local cache of deferred functions by executing them or moving into the
/// global cache.
///
/// Call this method after deferring execution of a function if you want to get it executed as
/// soon as possible. Flushing will make sure it is residing in in the global cache, so that
/// any thread has a chance of taking the function and executing it.
///
/// If this method is called from an [`unprotected`] guard, it is a no-op (nothing happens).
///
/// # Examples
///
/// ```
/// use crossbeam_epoch as epoch;
///
/// let guard = &amp;epoch::pin();
/// guard.defer(move || {
/// println!(&quot;This better be printed as soon as possible!&quot;);
/// });
/// guard.flush();
/// ```
</span><span class="kw">pub fn </span>flush(<span class="kw-2">&amp;</span><span class="self">self</span>) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(local) = <span class="kw">unsafe </span>{ <span class="self">self</span>.local.as_ref() } {
local.flush(<span class="self">self</span>);
}
}
<span class="doccomment">/// Unpins and then immediately re-pins the thread.
///
/// This method is useful when you don&#39;t want delay the advancement of the global epoch by
/// holding an old epoch. For safety, you should not maintain any guard-based reference across
/// the call (the latter is enforced by `&amp;mut self`). The thread will only be repinned if this
/// is the only active guard for the current thread.
///
/// If this method is called from an [`unprotected`] guard, then the call will be just no-op.
///
/// # Examples
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic};
/// use std::sync::atomic::Ordering::SeqCst;
///
/// let a = Atomic::new(777);
/// let mut guard = epoch::pin();
/// {
/// let p = a.load(SeqCst, &amp;guard);
/// assert_eq!(unsafe { p.as_ref() }, Some(&amp;777));
/// }
/// guard.repin();
/// {
/// let p = a.load(SeqCst, &amp;guard);
/// assert_eq!(unsafe { p.as_ref() }, Some(&amp;777));
/// }
/// # unsafe { drop(a.into_owned()); } // avoid leak
/// ```
</span><span class="kw">pub fn </span>repin(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(local) = <span class="kw">unsafe </span>{ <span class="self">self</span>.local.as_ref() } {
local.repin();
}
}
<span class="doccomment">/// Temporarily unpins the thread, executes the given function and then re-pins the thread.
///
/// This method is useful when you need to perform a long-running operation (e.g. sleeping)
/// and don&#39;t need to maintain any guard-based reference across the call (the latter is enforced
/// by `&amp;mut self`). The thread will only be unpinned if this is the only active guard for the
/// current thread.
///
/// If this method is called from an [`unprotected`] guard, then the passed function is called
/// directly without unpinning the thread.
///
/// # Examples
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic};
/// use std::sync::atomic::Ordering::SeqCst;
/// use std::thread;
/// use std::time::Duration;
///
/// let a = Atomic::new(777);
/// let mut guard = epoch::pin();
/// {
/// let p = a.load(SeqCst, &amp;guard);
/// assert_eq!(unsafe { p.as_ref() }, Some(&amp;777));
/// }
/// guard.repin_after(|| thread::sleep(Duration::from_millis(50)));
/// {
/// let p = a.load(SeqCst, &amp;guard);
/// assert_eq!(unsafe { p.as_ref() }, Some(&amp;777));
/// }
/// # unsafe { drop(a.into_owned()); } // avoid leak
/// ```
</span><span class="kw">pub fn </span>repin_after&lt;F, R&gt;(<span class="kw-2">&amp;mut </span><span class="self">self</span>, f: F) -&gt; R
<span class="kw">where
</span>F: FnOnce() -&gt; R,
{
<span class="kw">if let </span><span class="prelude-val">Some</span>(local) = <span class="kw">unsafe </span>{ <span class="self">self</span>.local.as_ref() } {
<span class="comment">// We need to acquire a handle here to ensure the Local doesn&#39;t
// disappear from under us.
</span>local.acquire_handle();
local.unpin();
}
<span class="comment">// Ensure the Guard is re-pinned even if the function panics
</span><span class="macro">defer! </span>{
<span class="kw">if let </span><span class="prelude-val">Some</span>(local) = <span class="kw">unsafe </span>{ <span class="self">self</span>.local.as_ref() } {
mem::forget(local.pin());
local.release_handle();
}
}
f()
}
<span class="doccomment">/// Returns the `Collector` associated with this guard.
///
/// This method is useful when you need to ensure that all guards used with
/// a data structure come from the same collector.
///
/// If this method is called from an [`unprotected`] guard, then `None` is returned.
///
/// # Examples
///
/// ```
/// use crossbeam_epoch as epoch;
///
/// let guard1 = epoch::pin();
/// let guard2 = epoch::pin();
/// assert!(guard1.collector() == guard2.collector());
/// ```
</span><span class="kw">pub fn </span>collector(<span class="kw-2">&amp;</span><span class="self">self</span>) -&gt; <span class="prelude-ty">Option</span>&lt;<span class="kw-2">&amp;</span>Collector&gt; {
<span class="kw">unsafe </span>{ <span class="self">self</span>.local.as_ref().map(|local| local.collector()) }
}
}
<span class="kw">impl </span>Drop <span class="kw">for </span>Guard {
<span class="attribute">#[inline]
</span><span class="kw">fn </span>drop(<span class="kw-2">&amp;mut </span><span class="self">self</span>) {
<span class="kw">if let </span><span class="prelude-val">Some</span>(local) = <span class="kw">unsafe </span>{ <span class="self">self</span>.local.as_ref() } {
local.unpin();
}
}
}
<span class="kw">impl </span>fmt::Debug <span class="kw">for </span>Guard {
<span class="kw">fn </span>fmt(<span class="kw-2">&amp;</span><span class="self">self</span>, f: <span class="kw-2">&amp;mut </span>fmt::Formatter&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; fmt::Result {
f.pad(<span class="string">&quot;Guard { .. }&quot;</span>)
}
}
<span class="doccomment">/// Returns a reference to a dummy guard that allows unprotected access to [`Atomic`]s.
///
/// This guard should be used in special occasions only. Note that it doesn&#39;t actually keep any
/// thread pinned - it&#39;s just a fake guard that allows loading from [`Atomic`]s unsafely.
///
/// Note that calling [`defer`] with a dummy guard will not defer the function - it will just
/// execute the function immediately.
///
/// If necessary, it&#39;s possible to create more dummy guards by cloning: `unprotected().clone()`.
///
/// # Safety
///
/// Loading and dereferencing data from an [`Atomic`] using this guard is safe only if the
/// [`Atomic`] is not being concurrently modified by other threads.
///
/// # Examples
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic};
/// use std::sync::atomic::Ordering::Relaxed;
///
/// let a = Atomic::new(7);
///
/// unsafe {
/// // Load `a` without pinning the current thread.
/// a.load(Relaxed, epoch::unprotected());
///
/// // It&#39;s possible to create more dummy guards by calling `clone()`.
/// let dummy = &amp;epoch::unprotected().clone();
///
/// dummy.defer(move || {
/// println!(&quot;This gets executed immediately.&quot;);
/// });
///
/// // Dropping `dummy` doesn&#39;t affect the current thread - it&#39;s just a noop.
/// }
/// # unsafe { drop(a.into_owned()); } // avoid leak
/// ```
///
/// The most common use of this function is when constructing or destructing a data structure.
///
/// For example, we can use a dummy guard in the destructor of a Treiber stack because at that
/// point no other thread could concurrently modify the [`Atomic`]s we are accessing.
///
/// If we were to actually pin the current thread during destruction, that would just unnecessarily
/// delay garbage collection and incur some performance cost, so in cases like these `unprotected`
/// is very helpful.
///
/// ```
/// use crossbeam_epoch::{self as epoch, Atomic};
/// use std::mem::ManuallyDrop;
/// use std::sync::atomic::Ordering::Relaxed;
///
/// struct Stack&lt;T&gt; {
/// head: Atomic&lt;Node&lt;T&gt;&gt;,
/// }
///
/// struct Node&lt;T&gt; {
/// data: ManuallyDrop&lt;T&gt;,
/// next: Atomic&lt;Node&lt;T&gt;&gt;,
/// }
///
/// impl&lt;T&gt; Drop for Stack&lt;T&gt; {
/// fn drop(&amp;mut self) {
/// unsafe {
/// // Unprotected load.
/// let mut node = self.head.load(Relaxed, epoch::unprotected());
///
/// while let Some(n) = node.as_ref() {
/// // Unprotected load.
/// let next = n.next.load(Relaxed, epoch::unprotected());
///
/// // Take ownership of the node, then drop its data and deallocate it.
/// let mut o = node.into_owned();
/// ManuallyDrop::drop(&amp;mut o.data);
/// drop(o);
///
/// node = next;
/// }
/// }
/// }
/// }
/// ```
///
/// [`Atomic`]: super::Atomic
/// [`defer`]: Guard::defer
</span><span class="attribute">#[inline]
</span><span class="kw">pub unsafe fn </span>unprotected() -&gt; <span class="kw-2">&amp;</span><span class="lifetime">&#39;static </span>Guard {
<span class="comment">// An unprotected guard is just a `Guard` with its field `local` set to null.
// We make a newtype over `Guard` because `Guard` isn&#39;t `Sync`, so can&#39;t be directly stored in
// a `static`
</span><span class="kw">struct </span>GuardWrapper(Guard);
<span class="kw">unsafe impl </span>Sync <span class="kw">for </span>GuardWrapper {}
<span class="kw">static </span>UNPROTECTED: GuardWrapper = GuardWrapper(Guard {
local: core::ptr::null(),
});
<span class="kw-2">&amp;</span>UNPROTECTED.<span class="number">0
</span>}
</code></pre></div>
</section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="crossbeam_epoch" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html>