mirror of
https://github.com/google/comprehensive-rust.git
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111 lines
3.4 KiB
Rust
111 lines
3.4 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::time;
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use tokio::sync::mpsc::{self, Sender};
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use tokio::sync::Mutex;
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struct Fork;
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struct Philosopher {
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name: String,
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// ANCHOR_END: Philosopher
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left_fork: Arc<Mutex<Fork>>,
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right_fork: Arc<Mutex<Fork>>,
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thoughts: 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)).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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// Pick up forks...
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// ANCHOR_END: Philosopher-eat
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let _first_lock = self.left_fork.lock().await;
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// Add a delay before picking the second fork to allow the execution
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// to transfer to another task
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time::sleep(time::Duration::from_millis(1)).await;
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let _second_lock = self.right_fork.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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static PHILOSOPHERS: &[&str] =
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&["Socrates", "Hypatia", "Plato", "Aristotle", "Pythagoras"];
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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 forks
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let mut forks = vec![];
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(0..PHILOSOPHERS.len()).for_each(|_| forks.push(Arc::new(Mutex::new(Fork))));
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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 left_fork = Arc::clone(&forks[i]);
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let right_fork = Arc::clone(&forks[(i + 1) % PHILOSOPHERS.len()]);
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// To avoid a deadlock, we have to break the symmetry
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// somewhere. This will swap the forks without deinitializing
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// either of them.
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if i == 0 {
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std::mem::swap(&mut left_fork, &mut right_fork);
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}
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philosophers.push(Philosopher {
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name: name.to_string(),
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left_fork,
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right_fork,
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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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