智能指针3： exercises/smart_pointers/arc1.rs

题目

rust

// arc1.rs
//
// In this exercise, we are given a Vec of u32 called "numbers" with values
// ranging from 0 to 99 -- [ 0, 1, 2, ..., 98, 99 ] We would like to use this
// set of numbers within 8 different threads simultaneously. Each thread is
// going to get the sum of every eighth value, with an offset.
//
// The first thread (offset 0), will sum 0, 8, 16, ...
// The second thread (offset 1), will sum 1, 9, 17, ...
// The third thread (offset 2), will sum 2, 10, 18, ...
// ...
// The eighth thread (offset 7), will sum 7, 15, 23, ...
//
// Because we are using threads, our values need to be thread-safe.  Therefore,
// we are using Arc.  We need to make a change in each of the two TODOs.
//
// Make this code compile by filling in a value for `shared_numbers` where the
// first TODO comment is, and create an initial binding for `child_numbers`
// where the second TODO comment is. Try not to create any copies of the
// `numbers` Vec!
//
// Execute `rustlings hint arc1` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

#![forbid(unused_imports)] // Do not change this, (or the next) line.
use std::sync::Arc;
use std::thread;

fn main() {
    let numbers: Vec<_> = (0..100u32).collect();
    let shared_numbers = // TODO
    let mut joinhandles = Vec::new();

    for offset in 0..8 {
        let child_numbers = // TODO
        joinhandles.push(thread::spawn(move || {
            let sum: u32 = child_numbers.iter().filter(|&&n| n % 8 == offset).sum();
            println!("Sum of offset {} is {}", offset, sum);
        }));
    }
    for handle in joinhandles.into_iter() {
        handle.join().unwrap();
    }
}

在本练习中，我们得到一个名为numbers的 u32 Vec，其值范围为 0 到 99 -- [ 0, 1, 2, ..., 98, 99 ] 我们希望使用这组数字同时在8个不同的线程中。每个线程都将获得每隔八个值的总和，并带有偏移量offset。

第一个线程（偏移量 0）将对 0, 8, 16, ... 求和
第二个线程（偏移量 1）将对 1, 9, 17, ... 求和
第三个线程（偏移量 2）将对 2, 10, 18, ... 求和
...
第八个线程（偏移量 7）将对 7, 15, 23, ... 求和

因为我们使用线程，所以我们的值需要是线程安全的。因此，我们使用 Arc。我们需要对这两个 TODO 分别进行更改。

通过在第一个 TODO 注释所在的位置填写 shared_numbers 的值来编译此代码，并在第二个 TODO 注释所在的位置为 child_numbers 创建初始绑定。尽量不要创建numbers Vec 的任何副本！

题目解析

在这个题目中shared_numbers应该时要在各个线程之间共享的，所以要声明为Arc类型。

而在线程中的child_numbers，只不过是Arc的clone。

rust

#![forbid(unused_imports)] // Do not change this, (or the next) line.
use std::sync::Arc;
use std::thread;

fn main() {
    let numbers: Vec<_> = (0..100u32).collect();
    let shared_numbers = // TODO 
    let shared_numbers = Arc::new(numbers);  
    let mut joinhandles = Vec::new();

    for offset in 0..8 {
        let child_numbers = // TODO 
        let child_numbers = shared_numbers.clone();  
        joinhandles.push(thread::spawn(move || {
            let sum: u32 = child_numbers.iter().filter(|&&n| n % 8 == offset).sum();
            println!("Sum of offset {} is {}", offset, sum);
        }));
    }
    for handle in joinhandles.into_iter() {
        handle.join().unwrap();
    }
}

智能指针3： exercises/smart_pointers/arc1.rs ​

题目 ​

题目解析 ​

参考资料 ​

智能指针3： exercises/smart_pointers/arc1.rs

题目

题目解析

参考资料