159 lines
7.8 KiB
HTML
159 lines
7.8 KiB
HTML
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<meta name="description" content="API documentation for the Rust `init` fn in crate `futures`.">
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<meta name="keywords" content="rust, rustlang, rust-lang, init">
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<title>futures::task::init - Rust</title>
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<div class="sidebar-menu">☰</div>
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<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>
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<section id='main' class="content">
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<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'>
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<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
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[<span class='inner'>−</span>]
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</a>
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</span><a class='srclink' href='../../src/futures/task_impl/core.rs.html#130-137' title='goto source code'>[src]</a></span></h1>
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<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>
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<p>This function is an unsafe low-level implementation detail typically only
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used by crates using <code>futures</code> in <code>no_std</code> context. Users of this crate
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who also use the standard library never need to invoke this function.</p>
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<p>The task system in the <code>futures</code> crate relies on some notion of "local
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storage" for the running thread and/or context. The <code>task::current</code> function
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can get invoked in any context, for example, and needs to be able to return
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a <code>Task</code>. Typically with the standard library this is supported with
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thread-local-storage, but this is not available in <code>no_std</code> contexts!</p>
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<p>This function is provided to allow <code>no_std</code> contexts to continue to be able
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to use the standard task system in this crate. The functions provided here
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will be used as-if they were thread-local-storage getters/setters. The <code>get</code>
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function provided is used to retrieve the current thread-local value of the
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task system's pointer, returning null if not initialized. The <code>set</code> function
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updates the value of the pointer.</p>
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<h1 id="return-value" class="section-header"><a href="#return-value">Return value</a></h1>
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<p>This function will return whether initialization succeeded or not. This
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function can be called concurrently and only the first invocation will
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succeed. If <code>false</code> is returned then the <code>get</code> and <code>set</code> pointers provided
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were <em>not</em> registered for use with the task system, but if <code>true</code> was
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provided then they will be called when the task system is used.</p>
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<p>Note that while safe to call concurrently it's recommended to still perform
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external synchronization when calling this function. This task system is
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not guaranteed to be ready to go until a call to this function returns
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<code>true</code>. In other words, if you call this function and see <code>false</code>, the
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task system may not be ready to go as another thread may still be calling
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<code>init</code>.</p>
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<h1 id="unsafety" class="section-header"><a href="#unsafety">Unsafety</a></h1>
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<p>This function is unsafe due to the requirements on the behavior of the
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<code>get</code> and <code>set</code> functions. The pointers returned from these functions must
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reflect the semantics specified above and must also be thread-local,
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depending on the definition of a "thread" in the calling context.</p>
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</div></section>
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