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32a8b4bf13
Use chopstick to explain why 2 are needed to eat. Limit async to 2 philosophers so they can deadlock in tokio. (Tested with [3, 4, 5] philosophers and they all were able to run without deadlock with lock ordering disabled.) --------- Co-authored-by: Sterling Stein <scubed2+git@gmail.com>
108 lines
3.2 KiB
Rust
108 lines
3.2 KiB
Rust
// Copyright 2023 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// ANCHOR: solution
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// ANCHOR: Philosopher
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use std::sync::Arc;
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use tokio::sync::{mpsc, Mutex};
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use tokio::time;
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struct Chopstick;
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struct Philosopher {
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name: String,
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// ANCHOR_END: Philosopher
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left_chopstick: Arc<Mutex<Chopstick>>,
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right_chopstick: Arc<Mutex<Chopstick>>,
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thoughts: mpsc::Sender<String>,
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}
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// ANCHOR: Philosopher-think
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impl Philosopher {
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async fn think(&self) {
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self.thoughts
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.send(format!("Eureka! {} has a new idea!", &self.name))
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.await
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.unwrap();
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}
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// ANCHOR_END: Philosopher-think
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// ANCHOR: Philosopher-eat
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async fn eat(&self) {
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// Keep trying until we have both chopsticks
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// ANCHOR_END: Philosopher-eat
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// Pick up chopsticks...
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let _left_chopstick = self.left_chopstick.lock().await;
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let _right_chopstick = self.right_chopstick.lock().await;
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// ANCHOR: Philosopher-eat-body
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println!("{} is eating...", &self.name);
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time::sleep(time::Duration::from_millis(5)).await;
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// ANCHOR_END: Philosopher-eat-body
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// The locks are dropped here
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// ANCHOR: Philosopher-eat-end
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}
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}
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// tokio scheduler doesn't deadlock with 5 philosophers, so have 2.
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static PHILOSOPHERS: &[&str] = &["Socrates", "Hypatia"];
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#[tokio::main]
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async fn main() {
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// ANCHOR_END: Philosopher-eat-end
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// Create chopsticks
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let mut chopsticks = vec![];
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PHILOSOPHERS
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.iter()
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.for_each(|_| chopsticks.push(Arc::new(Mutex::new(Chopstick))));
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// Create philosophers
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let (philosophers, mut rx) = {
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let mut philosophers = vec![];
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let (tx, rx) = mpsc::channel(10);
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for (i, name) in PHILOSOPHERS.iter().enumerate() {
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let mut left_chopstick = Arc::clone(&chopsticks[i]);
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let mut right_chopstick =
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Arc::clone(&chopsticks[(i + 1) % PHILOSOPHERS.len()]);
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if i == PHILOSOPHERS.len() - 1 {
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std::mem::swap(&mut left_chopstick, &mut right_chopstick);
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}
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philosophers.push(Philosopher {
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name: name.to_string(),
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left_chopstick,
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right_chopstick,
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thoughts: tx.clone(),
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});
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}
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(philosophers, rx)
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// tx is dropped here, so we don't need to explicitly drop it later
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};
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// Make them think and eat
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for phil in philosophers {
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tokio::spawn(async move {
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for _ in 0..100 {
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phil.think().await;
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phil.eat().await;
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}
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});
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}
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// Output their thoughts
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while let Some(thought) = rx.recv().await {
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println!("Here is a thought: {thought}");
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}
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}
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