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| </pre><pre class="rust"><code><span class="comment">// Copyright 2018 Developers of the Rand project.</span> |
| <span class="comment">//</span> |
| <span class="comment">// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or</span> |
| <span class="comment">// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license</span> |
| <span class="comment">// <LICENSE-MIT or https://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">//! Thread-local random number generator</span> |
| |
| <span class="kw">use</span> <span class="ident">core::cell::UnsafeCell</span>; |
| <span class="kw">use</span> <span class="ident">std::rc::Rc</span>; |
| <span class="kw">use</span> <span class="ident">std::thread_local</span>; |
| |
| <span class="kw">use</span> <span class="ident"><span class="kw">super</span>::std::Core</span>; |
| <span class="kw">use</span> <span class="ident"><span class="kw">crate</span>::rngs::adapter::ReseedingRng</span>; |
| <span class="kw">use</span> <span class="ident"><span class="kw">crate</span>::rngs::OsRng</span>; |
| <span class="kw">use</span> <span class="kw">crate</span>::{<span class="ident">CryptoRng</span>, <span class="ident">Error</span>, <span class="ident">RngCore</span>, <span class="ident">SeedableRng</span>}; |
| |
| <span class="comment">// Rationale for using `UnsafeCell` in `ThreadRng`:</span> |
| <span class="comment">//</span> |
| <span class="comment">// Previously we used a `RefCell`, with an overhead of ~15%. There will only</span> |
| <span class="comment">// ever be one mutable reference to the interior of the `UnsafeCell`, because</span> |
| <span class="comment">// we only have such a reference inside `next_u32`, `next_u64`, etc. Within a</span> |
| <span class="comment">// single thread (which is the definition of `ThreadRng`), there will only ever</span> |
| <span class="comment">// be one of these methods active at a time.</span> |
| <span class="comment">//</span> |
| <span class="comment">// A possible scenario where there could be multiple mutable references is if</span> |
| <span class="comment">// `ThreadRng` is used inside `next_u32` and co. But the implementation is</span> |
| <span class="comment">// completely under our control. We just have to ensure none of them use</span> |
| <span class="comment">// `ThreadRng` internally, which is nonsensical anyway. We should also never run</span> |
| <span class="comment">// `ThreadRng` in destructors of its implementation, which is also nonsensical.</span> |
| |
| |
| <span class="comment">// Number of generated bytes after which to reseed `ThreadRng`.</span> |
| <span class="comment">// According to benchmarks, reseeding has a noticeable impact with thresholds</span> |
| <span class="comment">// of 32 kB and less. We choose 64 kB to avoid significant overhead.</span> |
| <span class="kw">const</span> <span class="ident">THREAD_RNG_RESEED_THRESHOLD</span>: <span class="ident">u64</span> <span class="op">=</span> <span class="number">1024</span> <span class="op">*</span> <span class="number">64</span>; |
| |
| <span class="doccomment">/// A reference to the thread-local generator</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// An instance can be obtained via [`thread_rng`] or via `ThreadRng::default()`.</span> |
| <span class="doccomment">/// This handle is safe to use everywhere (including thread-local destructors),</span> |
| <span class="doccomment">/// though it is recommended not to use inside a fork handler.</span> |
| <span class="doccomment">/// The handle cannot be passed between threads (is not `Send` or `Sync`).</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// `ThreadRng` uses the same PRNG as [`StdRng`] for security and performance</span> |
| <span class="doccomment">/// and is automatically seeded from [`OsRng`].</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// Unlike `StdRng`, `ThreadRng` uses the [`ReseedingRng`] wrapper to reseed</span> |
| <span class="doccomment">/// the PRNG from fresh entropy every 64 kiB of random data as well as after a</span> |
| <span class="doccomment">/// fork on Unix (though not quite immediately; see documentation of</span> |
| <span class="doccomment">/// [`ReseedingRng`]).</span> |
| <span class="doccomment">/// Note that the reseeding is done as an extra precaution against side-channel</span> |
| <span class="doccomment">/// attacks and mis-use (e.g. if somehow weak entropy were supplied initially).</span> |
| <span class="doccomment">/// The PRNG algorithms used are assumed to be secure.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// [`ReseedingRng`]: crate::rngs::adapter::ReseedingRng</span> |
| <span class="doccomment">/// [`StdRng`]: crate::rngs::StdRng</span> |
| <span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">doc_cfg</span>, <span class="ident">doc</span>(<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">"std_rng"</span>))))]</span> |
| <span class="attribute">#[<span class="ident">derive</span>(<span class="ident">Clone</span>, <span class="ident">Debug</span>)]</span> |
| <span class="kw">pub</span> <span class="kw">struct</span> <span class="ident">ThreadRng</span> { |
| <span class="comment">// Rc is explicitly !Send and !Sync</span> |
| <span class="ident">rng</span>: <span class="ident">Rc</span><span class="op"><</span><span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">ReseedingRng</span><span class="op"><</span><span class="ident">Core</span>, <span class="ident">OsRng</span><span class="op">></span><span class="op">></span><span class="op">></span>, |
| } |
| |
| <span class="macro">thread_local!</span>( |
| <span class="comment">// We require Rc<..> to avoid premature freeing when thread_rng is used</span> |
| <span class="comment">// within thread-local destructors. See #968.</span> |
| <span class="kw">static</span> <span class="ident">THREAD_RNG_KEY</span>: <span class="ident">Rc</span><span class="op"><</span><span class="ident">UnsafeCell</span><span class="op"><</span><span class="ident">ReseedingRng</span><span class="op"><</span><span class="ident">Core</span>, <span class="ident">OsRng</span><span class="op">></span><span class="op">></span><span class="op">></span> <span class="op">=</span> { |
| <span class="kw">let</span> <span class="ident">r</span> <span class="op">=</span> <span class="ident">Core::from_rng</span>(<span class="ident">OsRng</span>).<span class="ident">unwrap_or_else</span>(<span class="op">|</span><span class="ident">err</span><span class="op">|</span> |
| <span class="macro">panic!</span>(<span class="string">"could not initialize thread_rng: {}"</span>, <span class="ident">err</span>)); |
| <span class="kw">let</span> <span class="ident">rng</span> <span class="op">=</span> <span class="ident">ReseedingRng::new</span>(<span class="ident">r</span>, |
| <span class="ident">THREAD_RNG_RESEED_THRESHOLD</span>, |
| <span class="ident">OsRng</span>); |
| <span class="ident">Rc::new</span>(<span class="ident">UnsafeCell::new</span>(<span class="ident">rng</span>)) |
| } |
| ); |
| |
| <span class="doccomment">/// Retrieve the lazily-initialized thread-local random number generator,</span> |
| <span class="doccomment">/// seeded by the system. Intended to be used in method chaining style,</span> |
| <span class="doccomment">/// e.g. `thread_rng().gen::<i32>()`, or cached locally, e.g.</span> |
| <span class="doccomment">/// `let mut rng = thread_rng();`. Invoked by the `Default` trait, making</span> |
| <span class="doccomment">/// `ThreadRng::default()` equivalent.</span> |
| <span class="doccomment">///</span> |
| <span class="doccomment">/// For more information see [`ThreadRng`].</span> |
| <span class="attribute">#[<span class="ident">cfg_attr</span>(<span class="ident">doc_cfg</span>, <span class="ident">doc</span>(<span class="ident">cfg</span>(<span class="ident">all</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">"std"</span>, <span class="ident">feature</span> <span class="op">=</span> <span class="string">"std_rng"</span>))))]</span> |
| <span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">thread_rng</span>() -> <span class="ident">ThreadRng</span> { |
| <span class="kw">let</span> <span class="ident">rng</span> <span class="op">=</span> <span class="ident">THREAD_RNG_KEY</span>.<span class="ident">with</span>(<span class="op">|</span><span class="ident">t</span><span class="op">|</span> <span class="ident">t</span>.<span class="ident">clone</span>()); |
| <span class="ident">ThreadRng</span> { <span class="ident">rng</span> } |
| } |
| |
| <span class="kw">impl</span> <span class="ident">Default</span> <span class="kw">for</span> <span class="ident">ThreadRng</span> { |
| <span class="kw">fn</span> <span class="ident">default</span>() -> <span class="ident">ThreadRng</span> { |
| <span class="ident"><span class="kw">crate</span>::prelude::thread_rng</span>() |
| } |
| } |
| |
| <span class="kw">impl</span> <span class="ident">RngCore</span> <span class="kw">for</span> <span class="ident">ThreadRng</span> { |
| <span class="attribute">#[<span class="ident">inline</span>(<span class="ident">always</span>)]</span> |
| <span class="kw">fn</span> <span class="ident">next_u32</span>(<span class="kw-2">&mut</span> <span class="self">self</span>) -> <span class="ident">u32</span> { |
| <span class="comment">// SAFETY: We must make sure to stop using `rng` before anyone else</span> |
| <span class="comment">// creates another mutable reference</span> |
| <span class="kw">let</span> <span class="ident">rng</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rng</span>.<span class="ident">get</span>() }; |
| <span class="ident">rng</span>.<span class="ident">next_u32</span>() |
| } |
| |
| <span class="attribute">#[<span class="ident">inline</span>(<span class="ident">always</span>)]</span> |
| <span class="kw">fn</span> <span class="ident">next_u64</span>(<span class="kw-2">&mut</span> <span class="self">self</span>) -> <span class="ident">u64</span> { |
| <span class="comment">// SAFETY: We must make sure to stop using `rng` before anyone else</span> |
| <span class="comment">// creates another mutable reference</span> |
| <span class="kw">let</span> <span class="ident">rng</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rng</span>.<span class="ident">get</span>() }; |
| <span class="ident">rng</span>.<span class="ident">next_u64</span>() |
| } |
| |
| <span class="kw">fn</span> <span class="ident">fill_bytes</span>(<span class="kw-2">&mut</span> <span class="self">self</span>, <span class="ident">dest</span>: <span class="kw-2">&mut</span> [<span class="ident">u8</span>]) { |
| <span class="comment">// SAFETY: We must make sure to stop using `rng` before anyone else</span> |
| <span class="comment">// creates another mutable reference</span> |
| <span class="kw">let</span> <span class="ident">rng</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rng</span>.<span class="ident">get</span>() }; |
| <span class="ident">rng</span>.<span class="ident">fill_bytes</span>(<span class="ident">dest</span>) |
| } |
| |
| <span class="kw">fn</span> <span class="ident">try_fill_bytes</span>(<span class="kw-2">&mut</span> <span class="self">self</span>, <span class="ident">dest</span>: <span class="kw-2">&mut</span> [<span class="ident">u8</span>]) -> <span class="prelude-ty">Result</span><span class="op"><</span>(), <span class="ident">Error</span><span class="op">></span> { |
| <span class="comment">// SAFETY: We must make sure to stop using `rng` before anyone else</span> |
| <span class="comment">// creates another mutable reference</span> |
| <span class="kw">let</span> <span class="ident">rng</span> <span class="op">=</span> <span class="kw">unsafe</span> { <span class="kw-2">&mut</span> <span class="kw-2">*</span><span class="self">self</span>.<span class="ident">rng</span>.<span class="ident">get</span>() }; |
| <span class="ident">rng</span>.<span class="ident">try_fill_bytes</span>(<span class="ident">dest</span>) |
| } |
| } |
| |
| <span class="kw">impl</span> <span class="ident">CryptoRng</span> <span class="kw">for</span> <span class="ident">ThreadRng</span> {} |
| |
| |
| <span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">test</span>)]</span> |
| <span class="kw">mod</span> <span class="ident">test</span> { |
| <span class="attribute">#[<span class="ident">test</span>]</span> |
| <span class="kw">fn</span> <span class="ident">test_thread_rng</span>() { |
| <span class="kw">use</span> <span class="ident"><span class="kw">crate</span>::Rng</span>; |
| <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">r</span> <span class="op">=</span> <span class="ident"><span class="kw">crate</span>::thread_rng</span>(); |
| <span class="ident">r</span>.<span class="ident">gen</span>::<span class="op"><</span><span class="ident">i32</span><span class="op">></span>(); |
| <span class="macro">assert_eq!</span>(<span class="ident">r</span>.<span class="ident">gen_range</span>(<span class="number">0</span>..<span class="number">1</span>), <span class="number">0</span>); |
| } |
| } |
| </code></pre></div> |
| </section><section id="search" class="content hidden"></section></div></main><div id="rustdoc-vars" data-root-path="../../../" data-current-crate="rand" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.60.0-nightly (1bd4fdc94 2022-01-12)" ></div> |
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