189 lines
No EOL
10 KiB
HTML
189 lines
No EOL
10 KiB
HTML
<!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 `Once` struct in crate `bitflags`.">
|
||
<meta name="keywords" content="rust, rustlang, rust-lang, Once">
|
||
|
||
<title>bitflags::__core::sync::Once - Rust</title>
|
||
|
||
<link rel="stylesheet" type="text/css" href="../../../rustdoc.css">
|
||
<link rel="stylesheet" type="text/css" href="../../../main.css">
|
||
|
||
|
||
|
||
|
||
</head>
|
||
<body class="rustdoc">
|
||
<!--[if lte IE 8]>
|
||
<div class="warning">
|
||
This old browser is unsupported and will most likely display funky
|
||
things.
|
||
</div>
|
||
<![endif]-->
|
||
|
||
|
||
|
||
<nav class="sidebar">
|
||
|
||
<p class='location'><a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>sync</a></p><script>window.sidebarCurrent = {name: 'Once', ty: 'struct', relpath: ''};</script><script defer src="sidebar-items.js"></script>
|
||
</nav>
|
||
|
||
<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">
|
||
</div>
|
||
</form>
|
||
</nav>
|
||
|
||
<section id='main' class="content struct">
|
||
<h1 class='fqn'><span class='in-band'>Struct <a href='../../index.html'>bitflags</a>::<wbr><a href='../index.html'>__core</a>::<wbr><a href='index.html'>sync</a>::<wbr><a class='struct' href=''>Once</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 id='src-10214' class='srclink' href='https://doc.rust-lang.org/nightly/std/sync/once/struct.Once.html?gotosrc=10214' title='goto source code'>[src]</a></span></h1>
|
||
<pre class='rust struct'>pub struct Once {
|
||
// some fields omitted
|
||
}</pre><span class="since">1.0.0</span><div class='docblock'><p>A synchronization primitive which can be used to run a one-time global
|
||
initialization. Useful for one-time initialization for FFI or related
|
||
functionality. This type can only be constructed with the <code>ONCE_INIT</code>
|
||
value.</p>
|
||
|
||
<h1 id='examples' class='section-header'><a href='#examples'>Examples</a></h1>
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>sync</span>::{<span class='ident'>Once</span>, <span class='ident'>ONCE_INIT</span>};
|
||
|
||
<span class='kw'>static</span> <span class='ident'>START</span>: <span class='ident'>Once</span> <span class='op'>=</span> <span class='ident'>ONCE_INIT</span>;
|
||
|
||
<span class='ident'>START</span>.<span class='ident'>call_once</span>(<span class='op'>||</span> {
|
||
<span class='comment'>// run initialization here</span>
|
||
});</pre>
|
||
</div><h2 id='methods'>Methods</h2><h3 class='impl'><code>impl <a class='struct' href='../../../bitflags/__core/sync/struct.Once.html' title='bitflags::__core::sync::Once'>Once</a></code></h3><div class='impl-items'><h4 id='method.new' class='method'><code>const fn <a href='#method.new' class='fnname'>new</a>() -> <a class='struct' href='../../../bitflags/__core/sync/struct.Once.html' title='bitflags::__core::sync::Once'>Once</a></code><span class="since">1.2.0</span></h4>
|
||
<div class='docblock'><p>Creates a new <code>Once</code> value.</p>
|
||
</div><h4 id='method.call_once' class='method'><code>fn <a href='#method.call_once' class='fnname'>call_once</a><F>(&'static self, f: F) <span class='where'>where F: <a class='trait' href='../../../bitflags/__core/ops/trait.FnOnce.html' title='bitflags::__core::ops::FnOnce'>FnOnce</a>() -> <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a></span></code></h4>
|
||
<div class='docblock'><p>Performs an initialization routine once and only once. The given closure
|
||
will be executed if this is the first time <code>call_once</code> has been called,
|
||
and otherwise the routine will <em>not</em> be invoked.</p>
|
||
|
||
<p>This method will block the calling thread if another initialization
|
||
routine is currently running.</p>
|
||
|
||
<p>When this function returns, it is guaranteed that some initialization
|
||
has run and completed (it may not be the closure specified). It is also
|
||
guaranteed that any memory writes performed by the executed closure can
|
||
be reliably observed by other threads at this point (there is a
|
||
happens-before relation between the closure and code executing after the
|
||
return).</p>
|
||
|
||
<h1 id='examples-1' class='section-header'><a href='#examples-1'>Examples</a></h1>
|
||
<pre class='rust rust-example-rendered'>
|
||
<span class='kw'>use</span> <span class='ident'>std</span>::<span class='ident'>sync</span>::{<span class='ident'>Once</span>, <span class='ident'>ONCE_INIT</span>};
|
||
|
||
<span class='kw'>static</span> <span class='kw-2'>mut</span> <span class='ident'>VAL</span>: <span class='ident'>usize</span> <span class='op'>=</span> <span class='number'>0</span>;
|
||
<span class='kw'>static</span> <span class='ident'>INIT</span>: <span class='ident'>Once</span> <span class='op'>=</span> <span class='ident'>ONCE_INIT</span>;
|
||
|
||
<span class='comment'>// Accessing a `static mut` is unsafe much of the time, but if we do so</span>
|
||
<span class='comment'>// in a synchronized fashion (e.g. write once or read all) then we're</span>
|
||
<span class='comment'>// good to go!</span>
|
||
<span class='comment'>//</span>
|
||
<span class='comment'>// This function will only call `expensive_computation` once, and will</span>
|
||
<span class='comment'>// otherwise always return the value returned from the first invocation.</span>
|
||
<span class='kw'>fn</span> <span class='ident'>get_cached_val</span>() <span class='op'>-></span> <span class='ident'>usize</span> {
|
||
<span class='kw'>unsafe</span> {
|
||
<span class='ident'>INIT</span>.<span class='ident'>call_once</span>(<span class='op'>||</span> {
|
||
<span class='ident'>VAL</span> <span class='op'>=</span> <span class='ident'>expensive_computation</span>();
|
||
});
|
||
<span class='ident'>VAL</span>
|
||
}
|
||
}
|
||
|
||
<span class='kw'>fn</span> <span class='ident'>expensive_computation</span>() <span class='op'>-></span> <span class='ident'>usize</span> {
|
||
<span class='comment'>// ...</span>
|
||
}</pre>
|
||
|
||
<h1 id='panics' class='section-header'><a href='#panics'>Panics</a></h1>
|
||
<p>The closure <code>f</code> will only be executed once if this is called
|
||
concurrently amongst many threads. If that closure panics, however, then
|
||
it will <em>poison</em> this <code>Once</code> instance, causing all future invocations of
|
||
<code>call_once</code> to also panic.</p>
|
||
|
||
<p>This is similar to <a href="struct.Mutex.html#poisoning">poisoning with mutexes</a>.</p>
|
||
</div><h4 id='method.call_once_force' class='method'><code>fn <a href='#method.call_once_force' class='fnname'>call_once_force</a><F>(&'static self, f: F) <span class='where'>where F: <a class='trait' href='../../../bitflags/__core/ops/trait.FnOnce.html' title='bitflags::__core::ops::FnOnce'>FnOnce</a>(&OnceState) -> <a class='primitive' href='https://doc.rust-lang.org/nightly/bitflags/primitive.tuple.html'>()</a></span></code></h4>
|
||
<div class='stability'><em class='stab unstable'>Unstable (<code>once_poison</code>)</em></div><div class='docblock'><p>Performs the same function as <code>call_once</code> except ignores poisoning.</p>
|
||
|
||
<p>If this <code>Once</code> has been poisoned (some initialization panicked) then
|
||
this function will continue to attempt to call initialization functions
|
||
until one of them doesn't panic.</p>
|
||
|
||
<p>The closure <code>f</code> is yielded a structure which can be used to query the
|
||
state of this <code>Once</code> (whether initialization has previously panicked or
|
||
not).
|
||
poisoned or not.</p>
|
||
</div></div><h2 id='implementations'>Trait Implementations</h2><h3 class='impl'><code>impl <a class='trait' href='../../../bitflags/__core/marker/trait.Sync.html' title='bitflags::__core::marker::Sync'>Sync</a> for <a class='struct' href='../../../bitflags/__core/sync/struct.Once.html' title='bitflags::__core::sync::Once'>Once</a></code></h3><div class='impl-items'></div><h3 class='impl'><code>impl <a class='trait' href='../../../bitflags/__core/marker/trait.Send.html' title='bitflags::__core::marker::Send'>Send</a> for <a class='struct' href='../../../bitflags/__core/sync/struct.Once.html' title='bitflags::__core::sync::Once'>Once</a></code></h3><div class='impl-items'></div></section>
|
||
<section id='search' class="content hidden"></section>
|
||
|
||
<section class="footer"></section>
|
||
|
||
<aside id="help" class="hidden">
|
||
<div>
|
||
<h1 class="hidden">Help</h1>
|
||
|
||
<div class="shortcuts">
|
||
<h2>Keyboard Shortcuts</h2>
|
||
|
||
<dl>
|
||
<dt>?</dt>
|
||
<dd>Show this help dialog</dd>
|
||
<dt>S</dt>
|
||
<dd>Focus the search field</dd>
|
||
<dt>⇤</dt>
|
||
<dd>Move up in search results</dd>
|
||
<dt>⇥</dt>
|
||
<dd>Move down in search results</dd>
|
||
<dt>⏎</dt>
|
||
<dd>Go to active search result</dd>
|
||
</dl>
|
||
</div>
|
||
|
||
<div class="infos">
|
||
<h2>Search Tricks</h2>
|
||
|
||
<p>
|
||
Prefix searches with a type followed by a colon (e.g.
|
||
<code>fn:</code>) to restrict the search to a given type.
|
||
</p>
|
||
|
||
<p>
|
||
Accepted types are: <code>fn</code>, <code>mod</code>,
|
||
<code>struct</code>, <code>enum</code>,
|
||
<code>trait</code>, <code>type</code>, <code>macro</code>,
|
||
and <code>const</code>.
|
||
</p>
|
||
|
||
<p>
|
||
Search functions by type signature (e.g.
|
||
<code>vec -> usize</code> or <code>* -> vec</code>)
|
||
</p>
|
||
</div>
|
||
</div>
|
||
</aside>
|
||
|
||
|
||
|
||
<script>
|
||
window.rootPath = "../../../";
|
||
window.currentCrate = "bitflags";
|
||
window.playgroundUrl = "";
|
||
</script>
|
||
<script src="../../../jquery.js"></script>
|
||
<script src="../../../main.js"></script>
|
||
|
||
<script defer src="../../../search-index.js"></script>
|
||
</body>
|
||
</html> |