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- <!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="API documentation for the Rust `init` fn in crate `futures`."><meta name="keywords" content="rust, rustlang, rust-lang, init"><title>futures::task::init - Rust</title><link rel="stylesheet" type="text/css" href="../../normalize.css"><link rel="stylesheet" type="text/css" href="../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" type="text/css" href="../../dark.css"><link rel="stylesheet" type="text/css" href="../../light.css" id="themeStyle"><script src="../../storage.js"></script></head><body class="rustdoc fn"><!--[if lte IE 8]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="sidebar"><div class="sidebar-menu">☰</div><div class="sidebar-elems"><p class='location'><a href='../index.html'>futures</a>::<wbr><a href='index.html'>task</a></p><script>window.sidebarCurrent = {name: 'init', ty: 'fn', relpath: ''};</script><script defer src="sidebar-items.js"></script></div></nav><div class="theme-picker"><button id="theme-picker" aria-label="Pick another theme!"><img src="../../brush.svg" width="18" alt="Pick another theme!"></button><div id="theme-choices"></div></div><script src="../../theme.js"></script><nav class="sub"><form class="search-form js-only"><div class="search-container"><input class="search-input" name="search" autocomplete="off" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><a id="settings-menu" href="../../settings.html"><img src="../../wheel.svg" width="18" alt="Change settings"></a></div></form></nav><section id="main" class="content"><h1 class='fqn'><span class='in-band'>Function <a href='../index.html'>futures</a>::<wbr><a href='index.html'>task</a>::<wbr><a class="fn" href=''>init</a></span><span class='out-of-band'><span id='render-detail'><a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class='inner'>−</span>]</a></span><a class='srclink' href='../../src/futures/task_impl/core.rs.html#130-137' title='goto source code'>[src]</a></span></h1><pre class='rust fn'>pub unsafe fn init(get: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.fn.html">fn</a>() -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.pointer.html">*mut </a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u8.html">u8</a>, set: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.fn.html">fn</a>(_: <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.pointer.html">*mut </a><a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.u8.html">u8</a>)) -> <a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.bool.html">bool</a></pre><div class='docblock'><p>Initialize the <code>futures</code> task system.</p>
- <p>This function is an unsafe low-level implementation detail typically only
- used by crates using <code>futures</code> in <code>no_std</code> context. Users of this crate
- who also use the standard library never need to invoke this function.</p>
- <p>The task system in the <code>futures</code> crate relies on some notion of "local
- storage" for the running thread and/or context. The <code>task::current</code> function
- can get invoked in any context, for example, and needs to be able to return
- a <code>Task</code>. Typically with the standard library this is supported with
- thread-local-storage, but this is not available in <code>no_std</code> contexts!</p>
- <p>This function is provided to allow <code>no_std</code> contexts to continue to be able
- to use the standard task system in this crate. The functions provided here
- will be used as-if they were thread-local-storage getters/setters. The <code>get</code>
- function provided is used to retrieve the current thread-local value of the
- task system's pointer, returning null if not initialized. The <code>set</code> function
- updates the value of the pointer.</p>
- <h1 id="return-value" class="section-header"><a href="#return-value">Return value</a></h1>
- <p>This function will return whether initialization succeeded or not. This
- function can be called concurrently and only the first invocation will
- succeed. If <code>false</code> is returned then the <code>get</code> and <code>set</code> pointers provided
- were <em>not</em> registered for use with the task system, but if <code>true</code> was
- provided then they will be called when the task system is used.</p>
- <p>Note that while safe to call concurrently it's recommended to still perform
- external synchronization when calling this function. This task system is
- not guaranteed to be ready to go until a call to this function returns
- <code>true</code>. In other words, if you call this function and see <code>false</code>, the
- task system may not be ready to go as another thread may still be calling
- <code>init</code>.</p>
- <h1 id="unsafety" class="section-header"><a href="#unsafety">Unsafety</a></h1>
- <p>This function is unsafe due to the requirements on the behavior of the
- <code>get</code> and <code>set</code> functions. The pointers returned from these functions must
- reflect the semantics specified above and must also be thread-local,
- depending on the definition of a "thread" in the calling context.</p>
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