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线程2： exercises/threads/threads2.rs
题目
rust
// threads2.rs
//
// Building on the last exercise, we want all of the threads to complete their
// work but this time the spawned threads need to be in charge of updating a
// shared value: JobStatus.jobs_completed
//
// Execute `rustlings hint threads2` or use the `hint` watch subcommand for a
// hint.
// I AM NOT DONE
use std::sync::Arc;
use std::thread;
use std::time::Duration;
struct JobStatus {
jobs_completed: u32,
}
fn main() {
let status = Arc::new(JobStatus { jobs_completed: 0 });
let mut handles = vec![];
for _ in 0..10 {
let status_shared = Arc::clone(&status);
let handle = thread::spawn(move || {
thread::sleep(Duration::from_millis(250));
// TODO: You must take an action before you update a shared value
status_shared.jobs_completed += 1;
});
handles.push(handle);
}
for handle in handles {
handle.join().unwrap();
// TODO: Print the value of the JobStatus.jobs_completed. Did you notice
// anything interesting in the output? Do you have to 'join' on all the
// handles?
println!("jobs completed {}", ???);
}
}在上一个练习的基础上，我们希望所有线程都完成其工作，但是这一次生成的线程需要负责更新共享值JobStatus.jobs_completed。
题目解析
共享的状态是status，类型为Arc，Arc是一个原子引用计数指针，允许安全、共享访问不可变数据。
但是在线程执行过程中，所有线程都要对status中的jobs_completed进行修改，就存在竞态，我们需要补充使用Mutex。
rust
use std::sync::Arc;
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;
struct JobStatus {
jobs_completed: u32,
}
fn main() {
let status = Arc::new(Mutex::new(JobStatus { jobs_completed: 0 }));
let mut handles = vec![];
for _ in 0..10 {
let status_shared = Arc::clone(&status);
let handle = thread::spawn(move || {
thread::sleep(Duration::from_millis(250));
// TODO: You must take an action before you update a shared value
status_shared.jobs_completed += 1;
status_shared.lock().unwrap().jobs_completed += 1;
});
handles.push(handle);
}
for handle in handles {
handle.join().unwrap();
// TODO: Print the value of the JobStatus.jobs_completed. Did you notice
// anything interesting in the output? Do you have to 'join' on all the
// handles?
println!("jobs completed {}", ???);
println!("jobs completed {}", status.lock().unwrap().jobs_completed);
}
}