Rust②食事する哲学者

下記の題材でソースコードを読み解いていく。
https://doc.rust-jp.rs/the-rust-programming-language-ja/1.6/book/dining-philosophers.html

◆事前準備

プロジェクトの開始-cargoを使用すること。

$ cd ~/projects
$ cargo new dining_philosophers --bin
$ cd dining_philosophers

簡単な構造

struct Philosopher {
    name: String,
}

impl Philosopher {
    fn new(name: &str) -> Philosopher {
        Philosopher {
            name: name.to_string(),
        }
    }
}

fn main() {
    let p1 = Philosopher::new("Judith Butler");
    let p2 = Philosopher::new("Gilles Deleuze");
    let p3 = Philosopher::new("Karl Marx");
    let p4 = Philosopher::new("Emma Goldman");
    let p5 = Philosopher::new("Michel Foucault");
}

解説
structで構造体を定義して
implで機能を定義する。Philosopherオブジェクトに引数の値を突っ込むこと
mainが動作を規定する

哲学者が一緒に食事するようにしたい場合

use std::thread;
use std::time::Duration;

struct Philosopher {
    name: String,
}

impl Philosopher {
    fn new(name: &str) -> Philosopher {
        Philosopher {
            name: name.to_string(),
        }
    }

    fn eat(&self) {
        println!("{} is eating.", self.name);

        thread::sleep(Duration::from_millis(1000));

        println!("{} is done eating.", self.name);
    }
}

fn main() {
    let philosophers = vec![
        Philosopher::new("Judith Butler"),
        Philosopher::new("Gilles Deleuze"),
        Philosopher::new("Karl Marx"),
        Philosopher::new("Emma Goldman"),
        Philosopher::new("Michel Foucault"),
    ];

    for p in &philosophers {
        p.eat();
    }
}

ライブラリが追加されること

use std::thread;
use std::time::Duration;

    fn eat(&self) {
        println!("{} is eating.", self.name);

        thread::sleep(Duration::from_millis(1000));

        println!("{} is done eating.", self.name);
    }

この期間を待つことの実装ができた。

平行性の実装

    let handles: Vec<_> = philosophers.into_iter().map(|p| {
        thread::spawn(move || {
            p.eat();
        })
    }).collect();

    for h in handles {
        h.join().unwrap();
    }

解説
これでマルチスレッドが実装できたらしい。すごいね。

古典的な並行処理問題の対応

use std::thread;
use std::time::Duration;
use std::sync::{Mutex, Arc};

struct Philosopher {
    name: String,
    left: usize,
    right: usize,
}

impl Philosopher {
    fn new(name: &str, left: usize, right: usize) -> Philosopher {
        Philosopher {
            name: name.to_string(),
            left: left,
            right: right,
        }
    }

    fn eat(&self, table: &Table) {
        let _left = table.forks[self.left].lock().unwrap();
        thread::sleep(Duration::from_millis(150));
        let _right = table.forks[self.right].lock().unwrap();

        println!("{} is eating.", self.name);

        thread::sleep(Duration::from_millis(1000));

        println!("{} is done eating.", self.name);
    }
}

struct Table {
    forks: Vec<Mutex<()>>,
}

fn main() {
    let table = Arc::new(Table { forks: vec![
        Mutex::new(()),
        Mutex::new(()),
        Mutex::new(()),
        Mutex::new(()),
        Mutex::new(()),
    ]});

    let philosophers = vec![
        Philosopher::new("Judith Butler", 0, 1),
        Philosopher::new("Gilles Deleuze", 1, 2),
        Philosopher::new("Karl Marx", 2, 3),
        Philosopher::new("Emma Goldman", 3, 4),
        Philosopher::new("Michel Foucault", 0, 4),
    ];

    let handles: Vec<_> = philosophers.into_iter().map(|p| {
        let table = table.clone();

        thread::spawn(move || {
            p.eat(&table);
        })
    }).collect();

    for h in handles {
        h.join().unwrap();
    }
}

解説
これもうわかんねえな。