//! Miscellaneous utilities. use std::cell::{Cell, UnsafeCell}; use std::num::Wrapping; use std::ops::{Deref, DerefMut}; use std::sync::atomic::{AtomicBool, Ordering}; use std::thread; use std::time::{Duration, Instant}; use crossbeam_utils::Backoff; /// Randomly shuffles a slice. pub fn shuffle(v: &mut [T]) { let len = v.len(); if len <= 1 { return; } thread_local! { static RNG: Cell> = Cell::new(Wrapping(1_406_868_647)); } let _ = RNG.try_with(|rng| { for i in 1..len { // This is the 32-bit variant of Xorshift. // // Source: https://en.wikipedia.org/wiki/Xorshift let mut x = rng.get(); x ^= x << 13; x ^= x >> 17; x ^= x << 5; rng.set(x); let x = x.0; let n = i + 1; // This is a fast alternative to `let j = x % n`. // // Author: Daniel Lemire // Source: https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/ let j = ((x as u64).wrapping_mul(n as u64) >> 32) as u32 as usize; v.swap(i, j); } }); } /// Sleeps until the deadline, or forever if the deadline isn't specified. pub fn sleep_until(deadline: Option) { loop { match deadline { None => thread::sleep(Duration::from_secs(1000)), Some(d) => { let now = Instant::now(); if now >= d { break; } thread::sleep(d - now); } } } } /// A simple spinlock. pub struct Spinlock { flag: AtomicBool, value: UnsafeCell, } impl Spinlock { /// Returns a new spinlock initialized with `value`. pub fn new(value: T) -> Spinlock { Spinlock { flag: AtomicBool::new(false), value: UnsafeCell::new(value), } } /// Locks the spinlock. pub fn lock(&self) -> SpinlockGuard<'_, T> { let backoff = Backoff::new(); while self.flag.swap(true, Ordering::Acquire) { backoff.snooze(); } SpinlockGuard { parent: self } } } /// A guard holding a spinlock locked. pub struct SpinlockGuard<'a, T> { parent: &'a Spinlock, } impl Drop for SpinlockGuard<'_, T> { fn drop(&mut self) { self.parent.flag.store(false, Ordering::Release); } } impl Deref for SpinlockGuard<'_, T> { type Target = T; fn deref(&self) -> &T { unsafe { &*self.parent.value.get() } } } impl DerefMut for SpinlockGuard<'_, T> { fn deref_mut(&mut self) -> &mut T { unsafe { &mut *self.parent.value.get() } } }