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Diffstat (limited to 'rand/src/rngs/thread.rs')
-rw-r--r-- | rand/src/rngs/thread.rs | 141 |
1 files changed, 0 insertions, 141 deletions
diff --git a/rand/src/rngs/thread.rs b/rand/src/rngs/thread.rs deleted file mode 100644 index 7977d85..0000000 --- a/rand/src/rngs/thread.rs +++ /dev/null @@ -1,141 +0,0 @@ -// Copyright 2018 Developers of the Rand project. -// -// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or -// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license -// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your -// option. This file may not be copied, modified, or distributed -// except according to those terms. - -//! Thread-local random number generator - -use std::cell::UnsafeCell; - -use {RngCore, CryptoRng, SeedableRng, Error}; -use rngs::adapter::ReseedingRng; -use rngs::EntropyRng; -use rand_hc::Hc128Core; - -// Rationale for using `UnsafeCell` in `ThreadRng`: -// -// Previously we used a `RefCell`, with an overhead of ~15%. There will only -// ever be one mutable reference to the interior of the `UnsafeCell`, because -// we only have such a reference inside `next_u32`, `next_u64`, etc. Within a -// single thread (which is the definition of `ThreadRng`), there will only ever -// be one of these methods active at a time. -// -// A possible scenario where there could be multiple mutable references is if -// `ThreadRng` is used inside `next_u32` and co. But the implementation is -// completely under our control. We just have to ensure none of them use -// `ThreadRng` internally, which is nonsensical anyway. We should also never run -// `ThreadRng` in destructors of its implementation, which is also nonsensical. -// -// The additional `Rc` is not strictly neccesary, and could be removed. For now -// it ensures `ThreadRng` stays `!Send` and `!Sync`, and implements `Clone`. - - -// Number of generated bytes after which to reseed `TreadRng`. -// -// The time it takes to reseed HC-128 is roughly equivalent to generating 7 KiB. -// We pick a treshold here that is large enough to not reduce the average -// performance too much, but also small enough to not make reseeding something -// that basically never happens. -const THREAD_RNG_RESEED_THRESHOLD: u64 = 32*1024*1024; // 32 MiB - -/// The type returned by [`thread_rng`], essentially just a reference to the -/// PRNG in thread-local memory. -/// -/// `ThreadRng` uses [`ReseedingRng`] wrapping the same PRNG as [`StdRng`], -/// which is reseeded after generating 32 MiB of random data. A single instance -/// is cached per thread and the returned `ThreadRng` is a reference to this -/// instance — hence `ThreadRng` is neither `Send` nor `Sync` but is safe to use -/// within a single thread. This RNG is seeded and reseeded via [`EntropyRng`] -/// as required. -/// -/// Note that the reseeding is done as an extra precaution against entropy -/// leaks and is in theory unnecessary — to predict `ThreadRng`'s output, an -/// attacker would have to either determine most of the RNG's seed or internal -/// state, or crack the algorithm used. -/// -/// Like [`StdRng`], `ThreadRng` is a cryptographically secure PRNG. The current -/// algorithm used is [HC-128], which is an array-based PRNG that trades memory -/// usage for better performance. This makes it similar to ISAAC, the algorithm -/// used in `ThreadRng` before rand 0.5. -/// -/// Cloning this handle just produces a new reference to the same thread-local -/// generator. -/// -/// [`thread_rng`]: ../fn.thread_rng.html -/// [`ReseedingRng`]: adapter/struct.ReseedingRng.html -/// [`StdRng`]: struct.StdRng.html -/// [`EntropyRng`]: struct.EntropyRng.html -/// [HC-128]: ../../rand_hc/struct.Hc128Rng.html -#[derive(Clone, Debug)] -pub struct ThreadRng { - // use of raw pointer implies type is neither Send nor Sync - rng: *mut ReseedingRng<Hc128Core, EntropyRng>, -} - -thread_local!( - static THREAD_RNG_KEY: UnsafeCell<ReseedingRng<Hc128Core, EntropyRng>> = { - let mut entropy_source = EntropyRng::new(); - let r = Hc128Core::from_rng(&mut entropy_source).unwrap_or_else(|err| - panic!("could not initialize thread_rng: {}", err)); - let rng = ReseedingRng::new(r, - THREAD_RNG_RESEED_THRESHOLD, - entropy_source); - UnsafeCell::new(rng) - } -); - -/// Retrieve the lazily-initialized thread-local random number generator, -/// seeded by the system. Intended to be used in method chaining style, -/// e.g. `thread_rng().gen::<i32>()`, or cached locally, e.g. -/// `let mut rng = thread_rng();`. Invoked by the `Default` trait, making -/// `ThreadRng::default()` equivelent. -/// -/// For more information see [`ThreadRng`]. -/// -/// [`ThreadRng`]: rngs/struct.ThreadRng.html -pub fn thread_rng() -> ThreadRng { - ThreadRng { rng: THREAD_RNG_KEY.with(|t| t.get()) } -} - -impl Default for ThreadRng { - fn default() -> ThreadRng { - ::prelude::thread_rng() - } -} - -impl RngCore for ThreadRng { - #[inline(always)] - fn next_u32(&mut self) -> u32 { - unsafe { (*self.rng).next_u32() } - } - - #[inline(always)] - fn next_u64(&mut self) -> u64 { - unsafe { (*self.rng).next_u64() } - } - - fn fill_bytes(&mut self, dest: &mut [u8]) { - unsafe { (*self.rng).fill_bytes(dest) } - } - - fn try_fill_bytes(&mut self, dest: &mut [u8]) -> Result<(), Error> { - unsafe { (*self.rng).try_fill_bytes(dest) } - } -} - -impl CryptoRng for ThreadRng {} - - -#[cfg(test)] -mod test { - #[test] - fn test_thread_rng() { - use Rng; - let mut r = ::thread_rng(); - r.gen::<i32>(); - assert_eq!(r.gen_range(0, 1), 0); - } -} |