69 lines
1.5 KiB
Rust
69 lines
1.5 KiB
Rust
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use std::sync::atomic::{spin_loop_hint, AtomicUsize, Ordering};
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use std::sync::Arc;
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pub struct TurnLock {
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turn: Arc<AtomicUsize>,
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index: usize,
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num_turns: usize,
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}
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impl TurnLock {
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pub fn new(num_turns: usize) -> Vec<Self> {
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let turn = Arc::new(AtomicUsize::new(0));
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let mut r = Vec::new();
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for i in 0..num_turns {
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r.push(TurnLock {
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turn: turn.clone(),
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index: i,
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num_turns,
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})
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}
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r
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}
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pub fn wait(&mut self) {
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while self.turn.load(Ordering::Acquire) != self.index {
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spin_loop_hint();
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}
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assert_eq!(self.turn.load(Ordering::Relaxed), self.index);
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}
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pub fn next(&mut self) {
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assert_eq!(self.turn.load(Ordering::Relaxed), self.index);
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let r = self.turn.compare_and_swap(
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self.index,
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(self.index + 1) % self.num_turns,
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Ordering::Release,
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);
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if r != self.index {
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panic!("Released lock out of turn");
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}
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}
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pub fn current(&self) -> usize {
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self.turn.load(Ordering::SeqCst)
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}
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}
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#[cfg(test)]
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mod tests {
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use crate::TurnLock;
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#[test]
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fn it_works() {
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assert_eq!(2 + 2, 4);
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}
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#[test]
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fn three_turns() {
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let mut v = TurnLock::new(3);
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v[0].wait();
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v[0].next();
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v[1].wait();
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v[1].next();
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v[2].wait();
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v[2].next();
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v[0].wait();
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v[0].next();
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assert_eq!(v[2].current(), 1);
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}
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}
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