<!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 to the Rust file `libcore/alloc.rs`."><meta name="keywords" content="rust, rustlang, rust-lang"><title>alloc.rs.html -- source</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><link rel="shortcut icon" href="https://doc.rust-lang.org/favicon.ico"></head><body class="rustdoc source"><!--[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><a href='../../core/index.html'><img src='https://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png' alt='logo' width='100'></a></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"><pre class="line-numbers"><span id="1"> 1</span>
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<span class="comment">// Copyright 2015 The Rust Project Developers. See the COPYRIGHT</span>
<span class="comment">// file at the top-level directory of this distribution and at</span>
<span class="comment">// http://rust-lang.org/COPYRIGHT.</span>
<span class="comment">//</span>
<span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span>
<span class="comment">// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span>
<span class="comment">// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your</span>
<span class="comment">// option. This file may not be copied, modified, or distributed</span>
<span class="comment">// except according to those terms.</span>
<span class="doccomment">//! Memory allocation APIs</span>
<span class="attribute">#![<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_module"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">use</span> <span class="ident">cmp</span>;
<span class="kw">use</span> <span class="ident">fmt</span>;
<span class="kw">use</span> <span class="ident">mem</span>;
<span class="kw">use</span> <span class="ident">usize</span>;
<span class="kw">use</span> <span class="ident">ptr</span>::{<span class="self">self</span>, <span class="ident">NonNull</span>};
<span class="kw">use</span> <span class="ident">num</span>::<span class="ident">NonZeroUsize</span>;
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_internals"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"0"</span>)]</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">stage0</span>)]</span>
<span class="kw">pub</span> <span class="kw">type</span> <span class="ident">Opaque</span> <span class="op">=</span> <span class="ident">u8</span>;
<span class="doccomment">/// Represents the combination of a starting address and</span>
<span class="doccomment">/// a total capacity of the returned block.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Excess</span>(<span class="kw">pub</span> <span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>, <span class="kw">pub</span> <span class="ident">usize</span>);
<span class="kw">fn</span> <span class="ident">size_align</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">-></span> (<span class="ident">usize</span>, <span class="ident">usize</span>) {
(<span class="ident">mem</span>::<span class="ident">size_of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(), <span class="ident">mem</span>::<span class="ident">align_of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>())
}
<span class="doccomment">/// Layout of a block of memory.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// An instance of `Layout` describes a particular layout of memory.</span>
<span class="doccomment">/// You build a `Layout` up as an input to give to an allocator.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// All layouts have an associated non-negative size and a</span>
<span class="doccomment">/// power-of-two alignment.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (Note however that layouts are *not* required to have positive</span>
<span class="doccomment">/// size, even though many allocators require that all memory</span>
<span class="doccomment">/// requests have positive size. A caller to the `Alloc::alloc`</span>
<span class="doccomment">/// method must either ensure that conditions like this are met, or</span>
<span class="doccomment">/// use specific allocators with looser requirements.)</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Copy</span>, <span class="ident">Clone</span>, <span class="ident">Debug</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">Layout</span> {
<span class="comment">// size of the requested block of memory, measured in bytes.</span>
<span class="ident">size_</span>: <span class="ident">usize</span>,
<span class="comment">// alignment of the requested block of memory, measured in bytes.</span>
<span class="comment">// we ensure that this is always a power-of-two, because API's</span>
<span class="comment">// like `posix_memalign` require it and it is a reasonable</span>
<span class="comment">// constraint to impose on Layout constructors.</span>
<span class="comment">//</span>
<span class="comment">// (However, we do not analogously require `align >= sizeof(void*)`,</span>
<span class="comment">// even though that is *also* a requirement of `posix_memalign`.)</span>
<span class="ident">align_</span>: <span class="ident">NonZeroUsize</span>,
}
<span class="kw">impl</span> <span class="ident">Layout</span> {
<span class="doccomment">/// Constructs a `Layout` from a given `size` and `align`,</span>
<span class="doccomment">/// or returns `LayoutErr` if either of the following conditions</span>
<span class="doccomment">/// are not met:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `align` must be a power of two,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `size`, when rounded up to the nearest multiple of `align`,</span>
<span class="doccomment">/// must not overflow (i.e. the rounded value must be less than</span>
<span class="doccomment">/// `usize::MAX`).</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">from_size_align</span>(<span class="ident">size</span>: <span class="ident">usize</span>, <span class="ident">align</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span>, <span class="ident">LayoutErr</span><span class="op">></span> {
<span class="kw">if</span> <span class="op">!</span><span class="ident">align</span>.<span class="ident">is_power_of_two</span>() {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () });
}
<span class="comment">// (power-of-two implies align != 0.)</span>
<span class="comment">// Rounded up size is:</span>
<span class="comment">// size_rounded_up = (size + align - 1) & !(align - 1);</span>
<span class="comment">//</span>
<span class="comment">// We know from above that align != 0. If adding (align - 1)</span>
<span class="comment">// does not overflow, then rounding up will be fine.</span>
<span class="comment">//</span>
<span class="comment">// Conversely, &-masking with !(align - 1) will subtract off</span>
<span class="comment">// only low-order-bits. Thus if overflow occurs with the sum,</span>
<span class="comment">// the &-mask cannot subtract enough to undo that overflow.</span>
<span class="comment">//</span>
<span class="comment">// Above implies that checking for summation overflow is both</span>
<span class="comment">// necessary and sufficient.</span>
<span class="kw">if</span> <span class="ident">size</span> <span class="op">></span> <span class="ident">usize</span>::<span class="ident">MAX</span> <span class="op">-</span> (<span class="ident">align</span> <span class="op">-</span> <span class="number">1</span>) {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () });
}
<span class="kw">unsafe</span> {
<span class="prelude-val">Ok</span>(<span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">size</span>, <span class="ident">align</span>))
}
}
<span class="doccomment">/// Creates a layout, bypassing all checks.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe as it does not verify the preconditions from</span>
<span class="doccomment">/// [`Layout::from_size_align`](#method.from_size_align).</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">from_size_align_unchecked</span>(<span class="ident">size</span>: <span class="ident">usize</span>, <span class="ident">align</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">Layout</span> { <span class="ident">size_</span>: <span class="ident">size</span>, <span class="ident">align_</span>: <span class="ident">NonZeroUsize</span>::<span class="ident">new_unchecked</span>(<span class="ident">align</span>) }
}
<span class="doccomment">/// The minimum size in bytes for a memory block of this layout.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">size</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> { <span class="self">self</span>.<span class="ident">size_</span> }
<span class="doccomment">/// The minimum byte alignment for a memory block of this layout.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">align</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="ident">usize</span> { <span class="self">self</span>.<span class="ident">align_</span>.<span class="ident">get</span>() }
<span class="doccomment">/// Constructs a `Layout` suitable for holding a value of type `T`.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">new</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>() <span class="op">-></span> <span class="self">Self</span> {
<span class="kw">let</span> (<span class="ident">size</span>, <span class="ident">align</span>) <span class="op">=</span> <span class="ident">size_align</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>();
<span class="comment">// Note that the align is guaranteed by rustc to be a power of two and</span>
<span class="comment">// the size+align combo is guaranteed to fit in our address space. As a</span>
<span class="comment">// result use the unchecked constructor here to avoid inserting code</span>
<span class="comment">// that panics if it isn't optimized well enough.</span>
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">Layout</span>::<span class="ident">from_size_align</span>(<span class="ident">size</span>, <span class="ident">align</span>).<span class="ident">is_ok</span>());
<span class="kw">unsafe</span> {
<span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">size</span>, <span class="ident">align</span>)
}
}
<span class="doccomment">/// Produces layout describing a record that could be used to</span>
<span class="doccomment">/// allocate backing structure for `T` (which could be a trait</span>
<span class="doccomment">/// or other unsized type like a slice).</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">for_value</span><span class="op"><</span><span class="ident">T</span>: <span class="question-mark">?</span><span class="ident">Sized</span><span class="op">></span>(<span class="ident">t</span>: <span class="kw-2">&</span><span class="ident">T</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="kw">let</span> (<span class="ident">size</span>, <span class="ident">align</span>) <span class="op">=</span> (<span class="ident">mem</span>::<span class="ident">size_of_val</span>(<span class="ident">t</span>), <span class="ident">mem</span>::<span class="ident">align_of_val</span>(<span class="ident">t</span>));
<span class="comment">// See rationale in `new` for why this us using an unsafe variant below</span>
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">Layout</span>::<span class="ident">from_size_align</span>(<span class="ident">size</span>, <span class="ident">align</span>).<span class="ident">is_ok</span>());
<span class="kw">unsafe</span> {
<span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">size</span>, <span class="ident">align</span>)
}
}
<span class="doccomment">/// Creates a layout describing the record that can hold a value</span>
<span class="doccomment">/// of the same layout as `self`, but that also is aligned to</span>
<span class="doccomment">/// alignment `align` (measured in bytes).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If `self` already meets the prescribed alignment, then returns</span>
<span class="doccomment">/// `self`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this method does not add any padding to the overall</span>
<span class="doccomment">/// size, regardless of whether the returned layout has a different</span>
<span class="doccomment">/// alignment. In other words, if `K` has size 16, `K.align_to(32)`</span>
<span class="doccomment">/// will *still* have size 16.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Panics</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Panics if the combination of `self.size()` and the given `align`</span>
<span class="doccomment">/// violates the conditions listed in</span>
<span class="doccomment">/// [`Layout::from_size_align`](#method.from_size_align).</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">align_to</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">align</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">Layout</span>::<span class="ident">from_size_align</span>(<span class="self">self</span>.<span class="ident">size</span>(), <span class="ident">cmp</span>::<span class="ident">max</span>(<span class="self">self</span>.<span class="ident">align</span>(), <span class="ident">align</span>)).<span class="ident">unwrap</span>()
}
<span class="doccomment">/// Returns the amount of padding we must insert after `self`</span>
<span class="doccomment">/// to ensure that the following address will satisfy `align`</span>
<span class="doccomment">/// (measured in bytes).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// E.g. if `self.size()` is 9, then `self.padding_needed_for(4)`</span>
<span class="doccomment">/// returns 3, because that is the minimum number of bytes of</span>
<span class="doccomment">/// padding required to get a 4-aligned address (assuming that the</span>
<span class="doccomment">/// corresponding memory block starts at a 4-aligned address).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The return value of this function has no meaning if `align` is</span>
<span class="doccomment">/// not a power-of-two.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that the utility of the returned value requires `align`</span>
<span class="doccomment">/// to be less than or equal to the alignment of the starting</span>
<span class="doccomment">/// address for the whole allocated block of memory. One way to</span>
<span class="doccomment">/// satisfy this constraint is to ensure `align <= self.align()`.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">padding_needed_for</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">align</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="ident">usize</span> {
<span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">size</span>();
<span class="comment">// Rounded up value is:</span>
<span class="comment">// len_rounded_up = (len + align - 1) & !(align - 1);</span>
<span class="comment">// and then we return the padding difference: `len_rounded_up - len`.</span>
<span class="comment">//</span>
<span class="comment">// We use modular arithmetic throughout:</span>
<span class="comment">//</span>
<span class="comment">// 1. align is guaranteed to be > 0, so align - 1 is always</span>
<span class="comment">// valid.</span>
<span class="comment">//</span>
<span class="comment">// 2. `len + align - 1` can overflow by at most `align - 1`,</span>
<span class="comment">// so the &-mask wth `!(align - 1)` will ensure that in the</span>
<span class="comment">// case of overflow, `len_rounded_up` will itself be 0.</span>
<span class="comment">// Thus the returned padding, when added to `len`, yields 0,</span>
<span class="comment">// which trivially satisfies the alignment `align`.</span>
<span class="comment">//</span>
<span class="comment">// (Of course, attempts to allocate blocks of memory whose</span>
<span class="comment">// size and padding overflow in the above manner should cause</span>
<span class="comment">// the allocator to yield an error anyway.)</span>
<span class="kw">let</span> <span class="ident">len_rounded_up</span> <span class="op">=</span> <span class="ident">len</span>.<span class="ident">wrapping_add</span>(<span class="ident">align</span>).<span class="ident">wrapping_sub</span>(<span class="number">1</span>)
<span class="op">&</span> <span class="op">!</span><span class="ident">align</span>.<span class="ident">wrapping_sub</span>(<span class="number">1</span>);
<span class="kw">return</span> <span class="ident">len_rounded_up</span>.<span class="ident">wrapping_sub</span>(<span class="ident">len</span>);
}
<span class="doccomment">/// Creates a layout describing the record for `n` instances of</span>
<span class="doccomment">/// `self`, with a suitable amount of padding between each to</span>
<span class="doccomment">/// ensure that each instance is given its requested size and</span>
<span class="doccomment">/// alignment. On success, returns `(k, offs)` where `k` is the</span>
<span class="doccomment">/// layout of the array and `offs` is the distance between the start</span>
<span class="doccomment">/// of each element in the array.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On arithmetic overflow, returns `LayoutErr`.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">repeat</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(<span class="self">Self</span>, <span class="ident">usize</span>), <span class="ident">LayoutErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">padded_size</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">size</span>().<span class="ident">checked_add</span>(<span class="self">self</span>.<span class="ident">padding_needed_for</span>(<span class="self">self</span>.<span class="ident">align</span>()))
.<span class="ident">ok_or</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () })<span class="question-mark">?</span>;
<span class="kw">let</span> <span class="ident">alloc_size</span> <span class="op">=</span> <span class="ident">padded_size</span>.<span class="ident">checked_mul</span>(<span class="ident">n</span>)
.<span class="ident">ok_or</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () })<span class="question-mark">?</span>;
<span class="kw">unsafe</span> {
<span class="comment">// self.align is already known to be valid and alloc_size has been</span>
<span class="comment">// padded already.</span>
<span class="prelude-val">Ok</span>((<span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">alloc_size</span>, <span class="self">self</span>.<span class="ident">align</span>()), <span class="ident">padded_size</span>))
}
}
<span class="doccomment">/// Creates a layout describing the record for `self` followed by</span>
<span class="doccomment">/// `next`, including any necessary padding to ensure that `next`</span>
<span class="doccomment">/// will be properly aligned. Note that the result layout will</span>
<span class="doccomment">/// satisfy the alignment properties of both `self` and `next`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `Some((k, offset))`, where `k` is layout of the concatenated</span>
<span class="doccomment">/// record and `offset` is the relative location, in bytes, of the</span>
<span class="doccomment">/// start of the `next` embedded within the concatenated record</span>
<span class="doccomment">/// (assuming that the record itself starts at offset 0).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On arithmetic overflow, returns `LayoutErr`.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">extend</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">next</span>: <span class="self">Self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(<span class="self">Self</span>, <span class="ident">usize</span>), <span class="ident">LayoutErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">new_align</span> <span class="op">=</span> <span class="ident">cmp</span>::<span class="ident">max</span>(<span class="self">self</span>.<span class="ident">align</span>(), <span class="ident">next</span>.<span class="ident">align</span>());
<span class="kw">let</span> <span class="ident">pad</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">padding_needed_for</span>(<span class="ident">next</span>.<span class="ident">align</span>());
<span class="kw">let</span> <span class="ident">offset</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">size</span>().<span class="ident">checked_add</span>(<span class="ident">pad</span>)
.<span class="ident">ok_or</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () })<span class="question-mark">?</span>;
<span class="kw">let</span> <span class="ident">new_size</span> <span class="op">=</span> <span class="ident">offset</span>.<span class="ident">checked_add</span>(<span class="ident">next</span>.<span class="ident">size</span>())
.<span class="ident">ok_or</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () })<span class="question-mark">?</span>;
<span class="kw">let</span> <span class="ident">layout</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">from_size_align</span>(<span class="ident">new_size</span>, <span class="ident">new_align</span>)<span class="question-mark">?</span>;
<span class="prelude-val">Ok</span>((<span class="ident">layout</span>, <span class="ident">offset</span>))
}
<span class="doccomment">/// Creates a layout describing the record for `n` instances of</span>
<span class="doccomment">/// `self`, with no padding between each instance.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that, unlike `repeat`, `repeat_packed` does not guarantee</span>
<span class="doccomment">/// that the repeated instances of `self` will be properly</span>
<span class="doccomment">/// aligned, even if a given instance of `self` is properly</span>
<span class="doccomment">/// aligned. In other words, if the layout returned by</span>
<span class="doccomment">/// `repeat_packed` is used to allocate an array, it is not</span>
<span class="doccomment">/// guaranteed that all elements in the array will be properly</span>
<span class="doccomment">/// aligned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On arithmetic overflow, returns `LayoutErr`.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">repeat_packed</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span>, <span class="ident">LayoutErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">size</span>().<span class="ident">checked_mul</span>(<span class="ident">n</span>).<span class="ident">ok_or</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () })<span class="question-mark">?</span>;
<span class="ident">Layout</span>::<span class="ident">from_size_align</span>(<span class="ident">size</span>, <span class="self">self</span>.<span class="ident">align</span>())
}
<span class="doccomment">/// Creates a layout describing the record for `self` followed by</span>
<span class="doccomment">/// `next` with no additional padding between the two. Since no</span>
<span class="doccomment">/// padding is inserted, the alignment of `next` is irrelevant,</span>
<span class="doccomment">/// and is not incorporated *at all* into the resulting layout.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `(k, offset)`, where `k` is layout of the concatenated</span>
<span class="doccomment">/// record and `offset` is the relative location, in bytes, of the</span>
<span class="doccomment">/// start of the `next` embedded within the concatenated record</span>
<span class="doccomment">/// (assuming that the record itself starts at offset 0).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (The `offset` is always the same as `self.size()`; we use this</span>
<span class="doccomment">/// signature out of convenience in matching the signature of</span>
<span class="doccomment">/// `extend`.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On arithmetic overflow, returns `LayoutErr`.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">extend_packed</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">next</span>: <span class="self">Self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(<span class="self">Self</span>, <span class="ident">usize</span>), <span class="ident">LayoutErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">new_size</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">size</span>().<span class="ident">checked_add</span>(<span class="ident">next</span>.<span class="ident">size</span>())
.<span class="ident">ok_or</span>(<span class="ident">LayoutErr</span> { <span class="ident">private</span>: () })<span class="question-mark">?</span>;
<span class="kw">let</span> <span class="ident">layout</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">from_size_align</span>(<span class="ident">new_size</span>, <span class="self">self</span>.<span class="ident">align</span>())<span class="question-mark">?</span>;
<span class="prelude-val">Ok</span>((<span class="ident">layout</span>, <span class="self">self</span>.<span class="ident">size</span>()))
}
<span class="doccomment">/// Creates a layout describing the record for a `[T; n]`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// On arithmetic overflow, returns `LayoutErr`.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">array</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="self">Self</span>, <span class="ident">LayoutErr</span><span class="op">></span> {
<span class="ident">Layout</span>::<span class="ident">new</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>()
.<span class="ident">repeat</span>(<span class="ident">n</span>)
.<span class="ident">map</span>(<span class="op">|</span>(<span class="ident">k</span>, <span class="ident">offs</span>)<span class="op">|</span> {
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">offs</span> <span class="op">==</span> <span class="ident">mem</span>::<span class="ident">size_of</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>());
<span class="ident">k</span>
})
}
}
<span class="doccomment">/// The parameters given to `Layout::from_size_align`</span>
<span class="doccomment">/// or some other `Layout` constructor</span>
<span class="doccomment">/// do not satisfy its documented constraints.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">LayoutErr</span> {
<span class="ident">private</span>: ()
}
<span class="comment">// (we need this for downstream impl of trait Error)</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"alloc_layout"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">LayoutErr</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="ident">f</span>.<span class="ident">write_str</span>(<span class="string">"invalid parameters to Layout::from_size_align"</span>)
}
}
<span class="doccomment">/// The `AllocErr` error indicates an allocation failure</span>
<span class="doccomment">/// that may be due to resource exhaustion or to</span>
<span class="doccomment">/// something wrong when combining the given input arguments with this</span>
<span class="doccomment">/// allocator.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">AllocErr</span>;
<span class="comment">// (we need this for downstream impl of trait Error)</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">AllocErr</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="ident">f</span>.<span class="ident">write_str</span>(<span class="string">"memory allocation failed"</span>)
}
}
<span class="doccomment">/// The `CannotReallocInPlace` error is used when `grow_in_place` or</span>
<span class="doccomment">/// `shrink_in_place` were unable to reuse the given memory block for</span>
<span class="doccomment">/// a requested layout.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">CannotReallocInPlace</span>;
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">impl</span> <span class="ident">CannotReallocInPlace</span> {
<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">description</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-></span> <span class="kw-2">&</span><span class="ident">str</span> {
<span class="string">"cannot reallocate allocator's memory in place"</span>
}
}
<span class="comment">// (we need this for downstream impl of trait Error)</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">impl</span> <span class="ident">fmt</span>::<span class="ident">Display</span> <span class="kw">for</span> <span class="ident">CannotReallocInPlace</span> {
<span class="kw">fn</span> <span class="ident">fmt</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">f</span>: <span class="kw-2">&</span><span class="kw-2">mut</span> <span class="ident">fmt</span>::<span class="ident">Formatter</span>) <span class="op">-></span> <span class="ident">fmt</span>::<span class="prelude-ty">Result</span> {
<span class="macro">write</span><span class="macro">!</span>(<span class="ident">f</span>, <span class="string">"{}"</span>, <span class="self">self</span>.<span class="ident">description</span>())
}
}
<span class="doccomment">/// Augments `AllocErr` with a CapacityOverflow variant.</span>
<span class="comment">// FIXME: should this be in libcore or liballoc?</span>
<span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">PartialEq</span>, <span class="ident">Eq</span>, <span class="ident">Debug</span>)]</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_reserve"</span>, <span class="ident">reason</span> <span class="op">=</span> <span class="string">"new API"</span>, <span class="ident">issue</span><span class="op">=</span><span class="string">"48043"</span>)]</span>
<span class="kw">pub</span> <span class="kw">enum</span> <span class="ident">CollectionAllocErr</span> {
<span class="doccomment">/// Error due to the computed capacity exceeding the collection's maximum</span>
<span class="doccomment">/// (usually `isize::MAX` bytes).</span>
<span class="ident">CapacityOverflow</span>,
<span class="doccomment">/// Error due to the allocator (see the `AllocErr` type's docs).</span>
<span class="ident">AllocErr</span>,
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_reserve"</span>, <span class="ident">reason</span> <span class="op">=</span> <span class="string">"new API"</span>, <span class="ident">issue</span><span class="op">=</span><span class="string">"48043"</span>)]</span>
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">AllocErr</span><span class="op">></span> <span class="kw">for</span> <span class="ident">CollectionAllocErr</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">from</span>(<span class="ident">AllocErr</span>: <span class="ident">AllocErr</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">CollectionAllocErr</span>::<span class="ident">AllocErr</span>
}
}
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"try_reserve"</span>, <span class="ident">reason</span> <span class="op">=</span> <span class="string">"new API"</span>, <span class="ident">issue</span><span class="op">=</span><span class="string">"48043"</span>)]</span>
<span class="kw">impl</span> <span class="ident">From</span><span class="op"><</span><span class="ident">LayoutErr</span><span class="op">></span> <span class="kw">for</span> <span class="ident">CollectionAllocErr</span> {
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">from</span>(<span class="kw">_</span>: <span class="ident">LayoutErr</span>) <span class="op">-></span> <span class="self">Self</span> {
<span class="ident">CollectionAllocErr</span>::<span class="ident">CapacityOverflow</span>
}
}
<span class="doccomment">/// A memory allocator that can be registered as the standard library’s default</span>
<span class="doccomment">/// though the `#[global_allocator]` attributes.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Some of the methods require that a memory block be *currently</span>
<span class="doccomment">/// allocated* via an allocator. This means that:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the starting address for that memory block was previously</span>
<span class="doccomment">/// returned by a previous call to an allocation method</span>
<span class="doccomment">/// such as `alloc`, and</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the memory block has not been subsequently deallocated, where</span>
<span class="doccomment">/// blocks are deallocated either by being passed to a deallocation</span>
<span class="doccomment">/// method such as `dealloc` or by being</span>
<span class="doccomment">/// passed to a reallocation method that returns a non-null pointer.</span>
<span class="doccomment">///</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Example</span>
<span class="doccomment">///</span>
<span class="doccomment">/// ```no_run</span>
<span class="doccomment">/// use std::alloc::{GlobalAlloc, Layout, alloc};</span>
<span class="doccomment">/// use std::ptr::null_mut;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// struct MyAllocator;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// unsafe impl GlobalAlloc for MyAllocator {</span>
<span class="doccomment">/// unsafe fn alloc(&self, _layout: Layout) -> *mut u8 { null_mut() }</span>
<span class="doccomment">/// unsafe fn dealloc(&self, _ptr: *mut u8, _layout: Layout) {}</span>
<span class="doccomment">/// }</span>
<span class="doccomment">///</span>
<span class="doccomment">/// #[global_allocator]</span>
<span class="doccomment">/// static A: MyAllocator = MyAllocator;</span>
<span class="doccomment">///</span>
<span class="doccomment">/// fn main() {</span>
<span class="doccomment">/// unsafe {</span>
<span class="doccomment">/// assert!(alloc(Layout::new::<u32>()).is_null())</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// }</span>
<span class="doccomment">/// ```</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Unsafety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `GlobalAlloc` trait is an `unsafe` trait for a number of reasons, and</span>
<span class="doccomment">/// implementors must ensure that they adhere to these contracts:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * It's undefined behavior if global allocators unwind. This restriction may</span>
<span class="doccomment">/// be lifted in the future, but currently a panic from any of these</span>
<span class="doccomment">/// functions may lead to memory unsafety.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `Layout` queries and calculations in general must be correct. Callers of</span>
<span class="doccomment">/// this trait are allowed to rely on the contracts defined on each method,</span>
<span class="doccomment">/// and implementors must ensure such contracts remain true.</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"global_alloc"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">trait</span> <span class="ident">GlobalAlloc</span> {
<span class="doccomment">/// Allocate memory as described by the given `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns a pointer to newly-allocated memory,</span>
<span class="doccomment">/// or null to indicate allocation failure.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure that `layout` has non-zero size.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (Extension subtraits might provide more specific bounds on</span>
<span class="doccomment">/// behavior, e.g. guarantee a sentinel address or a null pointer</span>
<span class="doccomment">/// in response to a zero-size allocation request.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The allocated block of memory may or may not be initialized.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning a null pointer indicates that either memory is exhausted</span>
<span class="doccomment">/// or `layout` does not meet allocator's size or alignment constraints.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Implementations are encouraged to return null on memory</span>
<span class="doccomment">/// exhaustion rather than aborting, but this is not</span>
<span class="doccomment">/// a strict requirement. (Specifically: it is *legal* to</span>
<span class="doccomment">/// implement this trait atop an underlying native allocation</span>
<span class="doccomment">/// library that aborts on memory exhaustion.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"global_alloc"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">alloc</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>;
<span class="doccomment">/// Deallocate the block of memory at the given `ptr` pointer with the given `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must denote a block of memory currently allocated via</span>
<span class="doccomment">/// this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `layout` must be the same layout that was used</span>
<span class="doccomment">/// to allocated that block of memory,</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"global_alloc"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">dealloc</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>);
<span class="doccomment">/// Behaves like `alloc`, but also ensures that the contents</span>
<span class="doccomment">/// are set to zero before being returned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe for the same reasons that `alloc` is.</span>
<span class="doccomment">/// However the allocated block of memory is guaranteed to be initialized.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning a null pointer indicates that either memory is exhausted</span>
<span class="doccomment">/// or `layout` does not meet allocator's size or alignment constraints,</span>
<span class="doccomment">/// just as in `alloc`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"global_alloc"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">alloc_zeroed</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span> {
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">layout</span>.<span class="ident">size</span>();
<span class="kw">let</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">layout</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">ptr</span>.<span class="ident">is_null</span>() {
<span class="ident">ptr</span>::<span class="ident">write_bytes</span>(<span class="ident">ptr</span>, <span class="number">0</span>, <span class="ident">size</span>);
}
<span class="ident">ptr</span>
}
<span class="doccomment">/// Shink or grow a block of memory to the given `new_size`.</span>
<span class="doccomment">/// The block is described by the given `ptr` pointer and `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this returns a non-null pointer, then ownership of the memory block</span>
<span class="doccomment">/// referenced by `ptr` has been transferred to this alloctor.</span>
<span class="doccomment">/// The memory may or may not have been deallocated,</span>
<span class="doccomment">/// and should be considered unusable (unless of course it was</span>
<span class="doccomment">/// transferred back to the caller again via the return value of</span>
<span class="doccomment">/// this method).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method returns null, then ownership of the memory</span>
<span class="doccomment">/// block has not been transferred to this allocator, and the</span>
<span class="doccomment">/// contents of the memory block are unaltered.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must be currently allocated via this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `layout` must be the same layout that was used</span>
<span class="doccomment">/// to allocated that block of memory,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `new_size` must be greater than zero.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,</span>
<span class="doccomment">/// must not overflow (i.e. the rounded value must be less than `usize::MAX`).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (Extension subtraits might provide more specific bounds on</span>
<span class="doccomment">/// behavior, e.g. guarantee a sentinel address or a null pointer</span>
<span class="doccomment">/// in response to a zero-size allocation request.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns null if the new layout does not meet the size</span>
<span class="doccomment">/// and alignment constraints of the allocator, or if reallocation</span>
<span class="doccomment">/// otherwise fails.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Implementations are encouraged to return null on memory</span>
<span class="doccomment">/// exhaustion rather than panicking or aborting, but this is not</span>
<span class="doccomment">/// a strict requirement. (Specifically: it is *legal* to</span>
<span class="doccomment">/// implement this trait atop an underlying native allocation</span>
<span class="doccomment">/// library that aborts on memory exhaustion.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to a</span>
<span class="doccomment">/// reallocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="attribute">#[<span class="ident">stable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"global_alloc"</span>, <span class="ident">since</span> <span class="op">=</span> <span class="string">"1.28.0"</span>)]</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">realloc</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">ptr</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>, <span class="ident">new_size</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span> {
<span class="kw">let</span> <span class="ident">new_layout</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">new_size</span>, <span class="ident">layout</span>.<span class="ident">align</span>());
<span class="kw">let</span> <span class="ident">new_ptr</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">new_layout</span>);
<span class="kw">if</span> <span class="op">!</span><span class="ident">new_ptr</span>.<span class="ident">is_null</span>() {
<span class="ident">ptr</span>::<span class="ident">copy_nonoverlapping</span>(
<span class="ident">ptr</span>,
<span class="ident">new_ptr</span>,
<span class="ident">cmp</span>::<span class="ident">min</span>(<span class="ident">layout</span>.<span class="ident">size</span>(), <span class="ident">new_size</span>),
);
<span class="self">self</span>.<span class="ident">dealloc</span>(<span class="ident">ptr</span>, <span class="ident">layout</span>);
}
<span class="ident">new_ptr</span>
}
}
<span class="doccomment">/// An implementation of `Alloc` can allocate, reallocate, and</span>
<span class="doccomment">/// deallocate arbitrary blocks of data described via `Layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Some of the methods require that a memory block be *currently</span>
<span class="doccomment">/// allocated* via an allocator. This means that:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the starting address for that memory block was previously</span>
<span class="doccomment">/// returned by a previous call to an allocation method (`alloc`,</span>
<span class="doccomment">/// `alloc_zeroed`, `alloc_excess`, `alloc_one`, `alloc_array`) or</span>
<span class="doccomment">/// reallocation method (`realloc`, `realloc_excess`, or</span>
<span class="doccomment">/// `realloc_array`), and</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the memory block has not been subsequently deallocated, where</span>
<span class="doccomment">/// blocks are deallocated either by being passed to a deallocation</span>
<span class="doccomment">/// method (`dealloc`, `dealloc_one`, `dealloc_array`) or by being</span>
<span class="doccomment">/// passed to a reallocation method (see above) that returns `Ok`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// A note regarding zero-sized types and zero-sized layouts: many</span>
<span class="doccomment">/// methods in the `Alloc` trait state that allocation requests</span>
<span class="doccomment">/// must be non-zero size, or else undefined behavior can result.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * However, some higher-level allocation methods (`alloc_one`,</span>
<span class="doccomment">/// `alloc_array`) are well-defined on zero-sized types and can</span>
<span class="doccomment">/// optionally support them: it is left up to the implementor</span>
<span class="doccomment">/// whether to return `Err`, or to return `Ok` with some pointer.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * If an `Alloc` implementation chooses to return `Ok` in this</span>
<span class="doccomment">/// case (i.e. the pointer denotes a zero-sized inaccessible block)</span>
<span class="doccomment">/// then that returned pointer must be considered "currently</span>
<span class="doccomment">/// allocated". On such an allocator, *all* methods that take</span>
<span class="doccomment">/// currently-allocated pointers as inputs must accept these</span>
<span class="doccomment">/// zero-sized pointers, *without* causing undefined behavior.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * In other words, if a zero-sized pointer can flow out of an</span>
<span class="doccomment">/// allocator, then that allocator must likewise accept that pointer</span>
<span class="doccomment">/// flowing back into its deallocation and reallocation methods.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Some of the methods require that a layout *fit* a memory block.</span>
<span class="doccomment">/// What it means for a layout to "fit" a memory block means (or</span>
<span class="doccomment">/// equivalently, for a memory block to "fit" a layout) is that the</span>
<span class="doccomment">/// following two conditions must hold:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// 1. The block's starting address must be aligned to `layout.align()`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// 2. The block's size must fall in the range `[use_min, use_max]`, where:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `use_min` is `self.usable_size(layout).0`, and</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `use_max` is the capacity that was (or would have been)</span>
<span class="doccomment">/// returned when (if) the block was allocated via a call to</span>
<span class="doccomment">/// `alloc_excess` or `realloc_excess`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the size of the layout most recently used to allocate the block</span>
<span class="doccomment">/// is guaranteed to be in the range `[use_min, use_max]`, and</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * a lower-bound on `use_max` can be safely approximated by a call to</span>
<span class="doccomment">/// `usable_size`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * if a layout `k` fits a memory block (denoted by `ptr`)</span>
<span class="doccomment">/// currently allocated via an allocator `a`, then it is legal to</span>
<span class="doccomment">/// use that layout to deallocate it, i.e. `a.dealloc(ptr, k);`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Unsafety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The `Alloc` trait is an `unsafe` trait for a number of reasons, and</span>
<span class="doccomment">/// implementors must ensure that they adhere to these contracts:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * Pointers returned from allocation functions must point to valid memory and</span>
<span class="doccomment">/// retain their validity until at least the instance of `Alloc` is dropped</span>
<span class="doccomment">/// itself.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `Layout` queries and calculations in general must be correct. Callers of</span>
<span class="doccomment">/// this trait are allowed to rely on the contracts defined on each method,</span>
<span class="doccomment">/// and implementors must ensure such contracts remain true.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that this list may get tweaked over time as clarifications are made in</span>
<span class="doccomment">/// the future.</span>
<span class="attribute">#[<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"allocator_api"</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">"32838"</span>)]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">trait</span> <span class="ident">Alloc</span> {
<span class="comment">// (Note: some existing allocators have unspecified but well-defined</span>
<span class="comment">// behavior in response to a zero size allocation request ;</span>
<span class="comment">// e.g. in C, `malloc` of 0 will either return a null pointer or a</span>
<span class="comment">// unique pointer, but will not have arbitrary undefined</span>
<span class="comment">// behavior.</span>
<span class="comment">// However in jemalloc for example,</span>
<span class="comment">// `mallocx(0)` is documented as undefined behavior.)</span>
<span class="doccomment">/// Returns a pointer meeting the size and alignment guarantees of</span>
<span class="doccomment">/// `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method returns an `Ok(addr)`, then the `addr` returned</span>
<span class="doccomment">/// will be non-null address pointing to a block of storage</span>
<span class="doccomment">/// suitable for holding an instance of `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned block of storage may or may not have its contents</span>
<span class="doccomment">/// initialized. (Extension subtraits might restrict this</span>
<span class="doccomment">/// behavior, e.g. to ensure initialization to particular sets of</span>
<span class="doccomment">/// bit patterns.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure that `layout` has non-zero size.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (Extension subtraits might provide more specific bounds on</span>
<span class="doccomment">/// behavior, e.g. guarantee a sentinel address or a null pointer</span>
<span class="doccomment">/// in response to a zero-size allocation request.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `layout` does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Implementations are encouraged to return `Err` on memory</span>
<span class="doccomment">/// exhaustion rather than panicking or aborting, but this is not</span>
<span class="doccomment">/// a strict requirement. (Specifically: it is *legal* to</span>
<span class="doccomment">/// implement this trait atop an underlying native allocation</span>
<span class="doccomment">/// library that aborts on memory exhaustion.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">alloc</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>, <span class="ident">AllocErr</span><span class="op">></span>;
<span class="doccomment">/// Deallocate the memory referenced by `ptr`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must denote a block of memory currently allocated via</span>
<span class="doccomment">/// this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `layout` must *fit* that block of memory,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * In addition to fitting the block of memory `layout`, the</span>
<span class="doccomment">/// alignment of the `layout` must match the alignment used</span>
<span class="doccomment">/// to allocate that block of memory.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">dealloc</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>, <span class="ident">layout</span>: <span class="ident">Layout</span>);
<span class="comment">// == ALLOCATOR-SPECIFIC QUANTITIES AND LIMITS ==</span>
<span class="comment">// usable_size</span>
<span class="doccomment">/// Returns bounds on the guaranteed usable size of a successful</span>
<span class="doccomment">/// allocation created with the specified `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// In particular, if one has a memory block allocated via a given</span>
<span class="doccomment">/// allocator `a` and layout `k` where `a.usable_size(k)` returns</span>
<span class="doccomment">/// `(l, u)`, then one can pass that block to `a.dealloc()` with a</span>
<span class="doccomment">/// layout in the size range [l, u].</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (All implementors of `usable_size` must ensure that</span>
<span class="doccomment">/// `l <= k.size() <= u`)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Both the lower- and upper-bounds (`l` and `u` respectively)</span>
<span class="doccomment">/// are provided, because an allocator based on size classes could</span>
<span class="doccomment">/// misbehave if one attempts to deallocate a block without</span>
<span class="doccomment">/// providing a correct value for its size (i.e., one within the</span>
<span class="doccomment">/// range `[l, u]`).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients who wish to make use of excess capacity are encouraged</span>
<span class="doccomment">/// to use the `alloc_excess` and `realloc_excess` instead, as</span>
<span class="doccomment">/// this method is constrained to report conservative values that</span>
<span class="doccomment">/// serve as valid bounds for *all possible* allocation method</span>
<span class="doccomment">/// calls.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// However, for clients that do not wish to track the capacity</span>
<span class="doccomment">/// returned by `alloc_excess` locally, this method is likely to</span>
<span class="doccomment">/// produce useful results.</span>
<span class="attribute">#[<span class="ident">inline</span>]</span>
<span class="kw">fn</span> <span class="ident">usable_size</span>(<span class="kw-2">&</span><span class="self">self</span>, <span class="ident">layout</span>: <span class="kw-2">&</span><span class="ident">Layout</span>) <span class="op">-></span> (<span class="ident">usize</span>, <span class="ident">usize</span>) {
(<span class="ident">layout</span>.<span class="ident">size</span>(), <span class="ident">layout</span>.<span class="ident">size</span>())
}
<span class="comment">// == METHODS FOR MEMORY REUSE ==</span>
<span class="comment">// realloc. alloc_excess, realloc_excess</span>
<span class="doccomment">/// Returns a pointer suitable for holding data described by</span>
<span class="doccomment">/// a new layout with `layout`’s alginment and a size given</span>
<span class="doccomment">/// by `new_size`. To</span>
<span class="doccomment">/// accomplish this, this may extend or shrink the allocation</span>
<span class="doccomment">/// referenced by `ptr` to fit the new layout.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this returns `Ok`, then ownership of the memory block</span>
<span class="doccomment">/// referenced by `ptr` has been transferred to this</span>
<span class="doccomment">/// allocator. The memory may or may not have been freed, and</span>
<span class="doccomment">/// should be considered unusable (unless of course it was</span>
<span class="doccomment">/// transferred back to the caller again via the return value of</span>
<span class="doccomment">/// this method).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this method returns `Err`, then ownership of the memory</span>
<span class="doccomment">/// block has not been transferred to this allocator, and the</span>
<span class="doccomment">/// contents of the memory block are unaltered.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must be currently allocated via this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `layout` must *fit* the `ptr` (see above). (The `new_size`</span>
<span class="doccomment">/// argument need not fit it.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `new_size` must be greater than zero.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `new_size`, when rounded up to the nearest multiple of `layout.align()`,</span>
<span class="doccomment">/// must not overflow (i.e. the rounded value must be less than `usize::MAX`).</span>
<span class="doccomment">///</span>
<span class="doccomment">/// (Extension subtraits might provide more specific bounds on</span>
<span class="doccomment">/// behavior, e.g. guarantee a sentinel address or a null pointer</span>
<span class="doccomment">/// in response to a zero-size allocation request.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `Err` only if the new layout</span>
<span class="doccomment">/// does not meet the allocator's size</span>
<span class="doccomment">/// and alignment constraints of the allocator, or if reallocation</span>
<span class="doccomment">/// otherwise fails.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Implementations are encouraged to return `Err` on memory</span>
<span class="doccomment">/// exhaustion rather than panicking or aborting, but this is not</span>
<span class="doccomment">/// a strict requirement. (Specifically: it is *legal* to</span>
<span class="doccomment">/// implement this trait atop an underlying native allocation</span>
<span class="doccomment">/// library that aborts on memory exhaustion.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to a</span>
<span class="doccomment">/// reallocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">realloc</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>,
<span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>,
<span class="ident">layout</span>: <span class="ident">Layout</span>,
<span class="ident">new_size</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>, <span class="ident">AllocErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">old_size</span> <span class="op">=</span> <span class="ident">layout</span>.<span class="ident">size</span>();
<span class="kw">if</span> <span class="ident">new_size</span> <span class="op">>=</span> <span class="ident">old_size</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(()) <span class="op">=</span> <span class="self">self</span>.<span class="ident">grow_in_place</span>(<span class="ident">ptr</span>, <span class="ident">layout</span>.<span class="ident">clone</span>(), <span class="ident">new_size</span>) {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">ptr</span>);
}
} <span class="kw">else</span> <span class="kw">if</span> <span class="ident">new_size</span> <span class="op"><</span> <span class="ident">old_size</span> {
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(()) <span class="op">=</span> <span class="self">self</span>.<span class="ident">shrink_in_place</span>(<span class="ident">ptr</span>, <span class="ident">layout</span>.<span class="ident">clone</span>(), <span class="ident">new_size</span>) {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(<span class="ident">ptr</span>);
}
}
<span class="comment">// otherwise, fall back on alloc + copy + dealloc.</span>
<span class="kw">let</span> <span class="ident">new_layout</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">new_size</span>, <span class="ident">layout</span>.<span class="ident">align</span>());
<span class="kw">let</span> <span class="ident">result</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">new_layout</span>);
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(<span class="ident">new_ptr</span>) <span class="op">=</span> <span class="ident">result</span> {
<span class="ident">ptr</span>::<span class="ident">copy_nonoverlapping</span>(<span class="ident">ptr</span>.<span class="ident">as_ptr</span>(),
<span class="ident">new_ptr</span>.<span class="ident">as_ptr</span>(),
<span class="ident">cmp</span>::<span class="ident">min</span>(<span class="ident">old_size</span>, <span class="ident">new_size</span>));
<span class="self">self</span>.<span class="ident">dealloc</span>(<span class="ident">ptr</span>, <span class="ident">layout</span>);
}
<span class="ident">result</span>
}
<span class="doccomment">/// Behaves like `alloc`, but also ensures that the contents</span>
<span class="doccomment">/// are set to zero before being returned.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe for the same reasons that `alloc` is.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `layout` does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints, just as in `alloc`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">alloc_zeroed</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>, <span class="ident">AllocErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">size</span> <span class="op">=</span> <span class="ident">layout</span>.<span class="ident">size</span>();
<span class="kw">let</span> <span class="ident">p</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">layout</span>);
<span class="kw">if</span> <span class="kw">let</span> <span class="prelude-val">Ok</span>(<span class="ident">p</span>) <span class="op">=</span> <span class="ident">p</span> {
<span class="ident">ptr</span>::<span class="ident">write_bytes</span>(<span class="ident">p</span>.<span class="ident">as_ptr</span>(), <span class="number">0</span>, <span class="ident">size</span>);
}
<span class="ident">p</span>
}
<span class="doccomment">/// Behaves like `alloc`, but also returns the whole size of</span>
<span class="doccomment">/// the returned block. For some `layout` inputs, like arrays, this</span>
<span class="doccomment">/// may include extra storage usable for additional data.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe for the same reasons that `alloc` is.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `layout` does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints, just as in `alloc`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">alloc_excess</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">layout</span>: <span class="ident">Layout</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">Excess</span>, <span class="ident">AllocErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">usable_size</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">usable_size</span>(<span class="kw-2">&</span><span class="ident">layout</span>);
<span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">layout</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">p</span><span class="op">|</span> <span class="ident">Excess</span>(<span class="ident">p</span>, <span class="ident">usable_size</span>.<span class="number">1</span>))
}
<span class="doccomment">/// Behaves like `realloc`, but also returns the whole size of</span>
<span class="doccomment">/// the returned block. For some `layout` inputs, like arrays, this</span>
<span class="doccomment">/// may include extra storage usable for additional data.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe for the same reasons that `realloc` is.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `layout` does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints, just as in `realloc`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to a</span>
<span class="doccomment">/// reallocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">realloc_excess</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>,
<span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>,
<span class="ident">layout</span>: <span class="ident">Layout</span>,
<span class="ident">new_size</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">Excess</span>, <span class="ident">AllocErr</span><span class="op">></span> {
<span class="kw">let</span> <span class="ident">new_layout</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">from_size_align_unchecked</span>(<span class="ident">new_size</span>, <span class="ident">layout</span>.<span class="ident">align</span>());
<span class="kw">let</span> <span class="ident">usable_size</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">usable_size</span>(<span class="kw-2">&</span><span class="ident">new_layout</span>);
<span class="self">self</span>.<span class="ident">realloc</span>(<span class="ident">ptr</span>, <span class="ident">layout</span>, <span class="ident">new_size</span>)
.<span class="ident">map</span>(<span class="op">|</span><span class="ident">p</span><span class="op">|</span> <span class="ident">Excess</span>(<span class="ident">p</span>, <span class="ident">usable_size</span>.<span class="number">1</span>))
}
<span class="doccomment">/// Attempts to extend the allocation referenced by `ptr` to fit `new_size`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this returns `Ok`, then the allocator has asserted that the</span>
<span class="doccomment">/// memory block referenced by `ptr` now fits `new_size`, and thus can</span>
<span class="doccomment">/// be used to carry data of a layout of that size and same alignment as</span>
<span class="doccomment">/// `layout`. (The allocator is allowed to</span>
<span class="doccomment">/// expend effort to accomplish this, such as extending the memory block to</span>
<span class="doccomment">/// include successor blocks, or virtual memory tricks.)</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Regardless of what this method returns, ownership of the</span>
<span class="doccomment">/// memory block referenced by `ptr` has not been transferred, and</span>
<span class="doccomment">/// the contents of the memory block are unaltered.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must be currently allocated via this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `layout` must *fit* the `ptr` (see above); note the</span>
<span class="doccomment">/// `new_size` argument need not fit it,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `new_size` must not be less than `layout.size()`,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `Err(CannotReallocInPlace)` when the allocator is</span>
<span class="doccomment">/// unable to assert that the memory block referenced by `ptr`</span>
<span class="doccomment">/// could fit `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`</span>
<span class="doccomment">/// function; clients are expected either to be able to recover from</span>
<span class="doccomment">/// `grow_in_place` failures without aborting, or to fall back on</span>
<span class="doccomment">/// another reallocation method before resorting to an abort.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">grow_in_place</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>,
<span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>,
<span class="ident">layout</span>: <span class="ident">Layout</span>,
<span class="ident">new_size</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">CannotReallocInPlace</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">ptr</span>; <span class="comment">// this default implementation doesn't care about the actual address.</span>
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">new_size</span> <span class="op">>=</span> <span class="ident">layout</span>.<span class="ident">size</span>());
<span class="kw">let</span> (<span class="ident">_l</span>, <span class="ident">u</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">usable_size</span>(<span class="kw-2">&</span><span class="ident">layout</span>);
<span class="comment">// _l <= layout.size() [guaranteed by usable_size()]</span>
<span class="comment">// layout.size() <= new_layout.size() [required by this method]</span>
<span class="kw">if</span> <span class="ident">new_size</span> <span class="op"><=</span> <span class="ident">u</span> {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(());
} <span class="kw">else</span> {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">CannotReallocInPlace</span>);
}
}
<span class="doccomment">/// Attempts to shrink the allocation referenced by `ptr` to fit `new_size`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this returns `Ok`, then the allocator has asserted that the</span>
<span class="doccomment">/// memory block referenced by `ptr` now fits `new_size`, and</span>
<span class="doccomment">/// thus can only be used to carry data of that smaller</span>
<span class="doccomment">/// layout. (The allocator is allowed to take advantage of this,</span>
<span class="doccomment">/// carving off portions of the block for reuse elsewhere.) The</span>
<span class="doccomment">/// truncated contents of the block within the smaller layout are</span>
<span class="doccomment">/// unaltered, and ownership of block has not been transferred.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// If this returns `Err`, then the memory block is considered to</span>
<span class="doccomment">/// still represent the original (larger) `layout`. None of the</span>
<span class="doccomment">/// block has been carved off for reuse elsewhere, ownership of</span>
<span class="doccomment">/// the memory block has not been transferred, and the contents of</span>
<span class="doccomment">/// the memory block are unaltered.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must be currently allocated via this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `layout` must *fit* the `ptr` (see above); note the</span>
<span class="doccomment">/// `new_size` argument need not fit it,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `new_size` must not be greater than `layout.size()`</span>
<span class="doccomment">/// (and must be greater than zero),</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returns `Err(CannotReallocInPlace)` when the allocator is</span>
<span class="doccomment">/// unable to assert that the memory block referenced by `ptr`</span>
<span class="doccomment">/// could fit `layout`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note that one cannot pass `CannotReallocInPlace` to the `handle_alloc_error`</span>
<span class="doccomment">/// function; clients are expected either to be able to recover from</span>
<span class="doccomment">/// `shrink_in_place` failures without aborting, or to fall back</span>
<span class="doccomment">/// on another reallocation method before resorting to an abort.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">shrink_in_place</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>,
<span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">u8</span><span class="op">></span>,
<span class="ident">layout</span>: <span class="ident">Layout</span>,
<span class="ident">new_size</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">CannotReallocInPlace</span><span class="op">></span> {
<span class="kw">let</span> <span class="kw">_</span> <span class="op">=</span> <span class="ident">ptr</span>; <span class="comment">// this default implementation doesn't care about the actual address.</span>
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">new_size</span> <span class="op"><=</span> <span class="ident">layout</span>.<span class="ident">size</span>());
<span class="kw">let</span> (<span class="ident">l</span>, <span class="ident">_u</span>) <span class="op">=</span> <span class="self">self</span>.<span class="ident">usable_size</span>(<span class="kw-2">&</span><span class="ident">layout</span>);
<span class="comment">// layout.size() <= _u [guaranteed by usable_size()]</span>
<span class="comment">// new_layout.size() <= layout.size() [required by this method]</span>
<span class="kw">if</span> <span class="ident">l</span> <span class="op"><=</span> <span class="ident">new_size</span> {
<span class="kw">return</span> <span class="prelude-val">Ok</span>(());
} <span class="kw">else</span> {
<span class="kw">return</span> <span class="prelude-val">Err</span>(<span class="ident">CannotReallocInPlace</span>);
}
}
<span class="comment">// == COMMON USAGE PATTERNS ==</span>
<span class="comment">// alloc_one, dealloc_one, alloc_array, realloc_array. dealloc_array</span>
<span class="doccomment">/// Allocates a block suitable for holding an instance of `T`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Captures a common usage pattern for allocators.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned block is suitable for passing to the</span>
<span class="doccomment">/// `alloc`/`realloc` methods of this allocator.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note to implementors: If this returns `Ok(ptr)`, then `ptr`</span>
<span class="doccomment">/// must be considered "currently allocated" and must be</span>
<span class="doccomment">/// acceptable input to methods such as `realloc` or `dealloc`,</span>
<span class="doccomment">/// *even if* `T` is a zero-sized type. In other words, if your</span>
<span class="doccomment">/// `Alloc` implementation overrides this method in a manner</span>
<span class="doccomment">/// that can return a zero-sized `ptr`, then all reallocation and</span>
<span class="doccomment">/// deallocation methods need to be similarly overridden to accept</span>
<span class="doccomment">/// such values as input.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `T` does not meet allocator's size or alignment constraints.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For zero-sized `T`, may return either of `Ok` or `Err`, but</span>
<span class="doccomment">/// will *not* yield undefined behavior.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">fn</span> <span class="ident">alloc_one</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">AllocErr</span><span class="op">></span>
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>
{
<span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">new</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>();
<span class="kw">if</span> <span class="ident">k</span>.<span class="ident">size</span>() <span class="op">></span> <span class="number">0</span> {
<span class="kw">unsafe</span> { <span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">k</span>).<span class="ident">map</span>(<span class="op">|</span><span class="ident">p</span><span class="op">|</span> <span class="ident">p</span>.<span class="ident">cast</span>()) }
} <span class="kw">else</span> {
<span class="prelude-val">Err</span>(<span class="ident">AllocErr</span>)
}
}
<span class="doccomment">/// Deallocates a block suitable for holding an instance of `T`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The given block must have been produced by this allocator,</span>
<span class="doccomment">/// and must be suitable for storing a `T` (in terms of alignment</span>
<span class="doccomment">/// as well as minimum and maximum size); otherwise yields</span>
<span class="doccomment">/// undefined behavior.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Captures a common usage pattern for allocators.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure both:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must denote a block of memory currently allocated via this allocator</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the layout of `T` must *fit* that block of memory.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">dealloc_one</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>)
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>
{
<span class="kw">let</span> <span class="ident">k</span> <span class="op">=</span> <span class="ident">Layout</span>::<span class="ident">new</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>();
<span class="kw">if</span> <span class="ident">k</span>.<span class="ident">size</span>() <span class="op">></span> <span class="number">0</span> {
<span class="self">self</span>.<span class="ident">dealloc</span>(<span class="ident">ptr</span>.<span class="ident">cast</span>(), <span class="ident">k</span>);
}
}
<span class="doccomment">/// Allocates a block suitable for holding `n` instances of `T`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Captures a common usage pattern for allocators.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned block is suitable for passing to the</span>
<span class="doccomment">/// `alloc`/`realloc` methods of this allocator.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Note to implementors: If this returns `Ok(ptr)`, then `ptr`</span>
<span class="doccomment">/// must be considered "currently allocated" and must be</span>
<span class="doccomment">/// acceptable input to methods such as `realloc` or `dealloc`,</span>
<span class="doccomment">/// *even if* `T` is a zero-sized type. In other words, if your</span>
<span class="doccomment">/// `Alloc` implementation overrides this method in a manner</span>
<span class="doccomment">/// that can return a zero-sized `ptr`, then all reallocation and</span>
<span class="doccomment">/// deallocation methods need to be similarly overridden to accept</span>
<span class="doccomment">/// such values as input.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `[T; n]` does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For zero-sized `T` or `n == 0`, may return either of `Ok` or</span>
<span class="doccomment">/// `Err`, but will *not* yield undefined behavior.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Always returns `Err` on arithmetic overflow.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to an</span>
<span class="doccomment">/// allocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">fn</span> <span class="ident">alloc_array</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">AllocErr</span><span class="op">></span>
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>
{
<span class="kw">match</span> <span class="ident">Layout</span>::<span class="ident">array</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">n</span>) {
<span class="prelude-val">Ok</span>(<span class="kw-2">ref</span> <span class="ident">layout</span>) <span class="kw">if</span> <span class="ident">layout</span>.<span class="ident">size</span>() <span class="op">></span> <span class="number">0</span> <span class="op">=></span> {
<span class="kw">unsafe</span> {
<span class="self">self</span>.<span class="ident">alloc</span>(<span class="ident">layout</span>.<span class="ident">clone</span>()).<span class="ident">map</span>(<span class="op">|</span><span class="ident">p</span><span class="op">|</span> <span class="ident">p</span>.<span class="ident">cast</span>())
}
}
<span class="kw">_</span> <span class="op">=></span> <span class="prelude-val">Err</span>(<span class="ident">AllocErr</span>),
}
}
<span class="doccomment">/// Reallocates a block previously suitable for holding `n_old`</span>
<span class="doccomment">/// instances of `T`, returning a block suitable for holding</span>
<span class="doccomment">/// `n_new` instances of `T`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Captures a common usage pattern for allocators.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// The returned block is suitable for passing to the</span>
<span class="doccomment">/// `alloc`/`realloc` methods of this allocator.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure all of the following:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must be currently allocated via this allocator,</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the layout of `[T; n_old]` must *fit* that block of memory.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either memory is exhausted or</span>
<span class="doccomment">/// `[T; n_new]` does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// For zero-sized `T` or `n_new == 0`, may return either of `Ok` or</span>
<span class="doccomment">/// `Err`, but will *not* yield undefined behavior.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Always returns `Err` on arithmetic overflow.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Clients wishing to abort computation in response to a</span>
<span class="doccomment">/// reallocation error are encouraged to call the [`handle_alloc_error`] function,</span>
<span class="doccomment">/// rather than directly invoking `panic!` or similar.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// [`handle_alloc_error`]: ../../alloc/alloc/fn.handle_alloc_error.html</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">realloc_array</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>,
<span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>,
<span class="ident">n_old</span>: <span class="ident">usize</span>,
<span class="ident">n_new</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span><span class="ident">NonNull</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">AllocErr</span><span class="op">></span>
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>
{
<span class="kw">match</span> (<span class="ident">Layout</span>::<span class="ident">array</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">n_old</span>), <span class="ident">Layout</span>::<span class="ident">array</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">n_new</span>)) {
(<span class="prelude-val">Ok</span>(<span class="kw-2">ref</span> <span class="ident">k_old</span>), <span class="prelude-val">Ok</span>(<span class="kw-2">ref</span> <span class="ident">k_new</span>)) <span class="kw">if</span> <span class="ident">k_old</span>.<span class="ident">size</span>() <span class="op">></span> <span class="number">0</span> <span class="op">&&</span> <span class="ident">k_new</span>.<span class="ident">size</span>() <span class="op">></span> <span class="number">0</span> <span class="op">=></span> {
<span class="macro">debug_assert</span><span class="macro">!</span>(<span class="ident">k_old</span>.<span class="ident">align</span>() <span class="op">==</span> <span class="ident">k_new</span>.<span class="ident">align</span>());
<span class="self">self</span>.<span class="ident">realloc</span>(<span class="ident">ptr</span>.<span class="ident">cast</span>(), <span class="ident">k_old</span>.<span class="ident">clone</span>(), <span class="ident">k_new</span>.<span class="ident">size</span>()).<span class="ident">map</span>(<span class="ident">NonNull</span>::<span class="ident">cast</span>)
}
<span class="kw">_</span> <span class="op">=></span> {
<span class="prelude-val">Err</span>(<span class="ident">AllocErr</span>)
}
}
}
<span class="doccomment">/// Deallocates a block suitable for holding `n` instances of `T`.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Captures a common usage pattern for allocators.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Safety</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This function is unsafe because undefined behavior can result</span>
<span class="doccomment">/// if the caller does not ensure both:</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * `ptr` must denote a block of memory currently allocated via this allocator</span>
<span class="doccomment">///</span>
<span class="doccomment">/// * the layout of `[T; n]` must *fit* that block of memory.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// # Errors</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Returning `Err` indicates that either `[T; n]` or the given</span>
<span class="doccomment">/// memory block does not meet allocator's size or alignment</span>
<span class="doccomment">/// constraints.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// Always returns `Err` on arithmetic overflow.</span>
<span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">dealloc_array</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">ptr</span>: <span class="ident">NonNull</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>, <span class="ident">n</span>: <span class="ident">usize</span>) <span class="op">-></span> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">AllocErr</span><span class="op">></span>
<span class="kw">where</span> <span class="self">Self</span>: <span class="ident">Sized</span>
{
<span class="kw">match</span> <span class="ident">Layout</span>::<span class="ident">array</span>::<span class="op"><</span><span class="ident">T</span><span class="op">></span>(<span class="ident">n</span>) {
<span class="prelude-val">Ok</span>(<span class="kw-2">ref</span> <span class="ident">k</span>) <span class="kw">if</span> <span class="ident">k</span>.<span class="ident">size</span>() <span class="op">></span> <span class="number">0</span> <span class="op">=></span> {
<span class="prelude-val">Ok</span>(<span class="self">self</span>.<span class="ident">dealloc</span>(<span class="ident">ptr</span>.<span class="ident">cast</span>(), <span class="ident">k</span>.<span class="ident">clone</span>()))
}
<span class="kw">_</span> <span class="op">=></span> {
<span class="prelude-val">Err</span>(<span class="ident">AllocErr</span>)
}
}
}
}
</pre>
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