Rust：并发编程（concurrent programming）

得益于所有权系统以及类型系统，Rust有着非常优异的并发性能。

1. 线程的基本应用

创建线程：

use std::thread;
use std::time::Duration;
fn main() {thread::spawn(|| {for i in 1..10 {println!("hi number {} from the spawned thread!", i);thread::sleep(Duration::from_millis(1));}});for i in 1..5 {println!("hi number {} from the main thread!", i);thread::sleep(Duration::from_millis(1));}
}

hi number 1 from the main thread!
hi number 1 from the spawned thread!
hi number 2 from the spawned thread!
hi number 2 from the main thread!
hi number 3 from the main thread!
hi number 3 from the spawned thread!
hi number 4 from the spawned thread!
hi number 4 from the main thread!
hi number 5 from the spawned thread!

需要注意的是，当主线程结束，不管thread::spawn创建的子线程是否执行完毕，程序都会结束。所以子线程的print语句只执行到了i=5。

使用Join()让主线程等待子线程执行完毕:

如果我们想让子线程执行完毕，可以将thread::spawn赋给变量，然后调用join。在rust中，thread::spawn返回的type是JoinHandle。

use std::thread;
use std::time::Duration;
fn main() {//thread::spawn创建线程后返回JoinHandle 类型给handlelet handle = thread::spawn(|| {for i in 1..10 {println!("hi number {} from the spawned thread!", i);thread::sleep(Duration::from_millis(1));}});for i in 1..5 {println!("hi number {} from the main thread!", i);thread::sleep(Duration::from_millis(1));}//调用join，让主线程等待至子线程执行完毕//unwrap的作用：请求返回结果，如果报错就会panic并停止程序handle.join().unwrap();
}

hi number 1 from the main thread!
hi number 2 from the main thread!
hi number 1 from the spawned thread!
hi number 3 from the main thread!
hi number 2 from the spawned thread!
hi number 4 from the main thread!
hi number 3 from the spawned thread!
hi number 4 from the spawned thread!
hi number 5 from the spawned thread!
hi number 6 from the spawned thread!
hi number 7 from the spawned thread!
hi number 8 from the spawned thread!
hi number 9 from the spawned thread!

使用Move让线程获得变量所有权

在Rust里，当闭包函数使用外界环境的变量时，编译器会推断闭包函数该采用借用，还是获取变量所有权的方式。当创建的子线程需要使用主线程的数据时，由于闭包函数运行子线程环境中而无法确定借用是否一直有效，所以需要使用move来使变量所有权移交至子线程的闭包函数。

use std::thread;
fn main() {let v = vec![1, 2, 3];//使用move移交所有权至子线程let handle = thread::spawn(move|| {println!("Here's a vector: {:?}", v);});handle.join().unwrap();
}

2. 线程通信机制：channel，transmitter与receiver

Rust book中将rust的线程通信的channel比作一条河，数据比作橡皮鸭。橡皮鸭从上游（transmitter）顺流而下到下游（receiver）。Rust中实现线程通信的标准库为mpsc，是multiple producer; single consumer的缩写。意思是在rust线程通信机制中，可以有多个数据发送端，然后像河流汇聚到大海一般，最终由一个接受端接收。

use std::thread;
use std::sync::mpsc;
fn main() {//创建channel//mpsc::channel()返回一个tuple，包含transmitter:tx , receiver:rx//在很多领域tx，rx都被当做是transmitter与receiver的缩写//所以rust book的这个例子也以此来命名let (tx, rx) = mpsc::channel();thread::spawn(move || {let val = String::from("hi");//transmitter从子线程发送数据tx.send(val).unwrap();//需要注意的是，此时val的所有权也被移交给了数据的接收线程});//主线程接受子线程数据let received = rx.recv().unwrap();println!("Got: {}", received);
}

Got: hi

Sending Multiple Values and Seeing the Receiver Waiting：

为了直观展现出两个线程通过channel保持communicating，对上述代码做出一点修改：使用for循环发送多条value，并且每次发送间隔1秒。同样也以for循环在主线程中接收数据，这时rx被当作一个iterator。每当接收到一条数据，for循环就会执行一次。直到数据发送完毕，channel关闭。

use std::thread;
use std::sync::mpsc;
use std::time::Duration;
fn main() {let (tx, rx) = mpsc::channel();thread::spawn(move || {let vals = vec![String::from("hi"),String::from("from"),String::from("the"),String::from("thread"),];for val in vals {tx.send(val).unwrap();thread::sleep(Duration::from_secs(1));}});for received in rx {println!("Got: {}", received);}
}

应该可以直观的看到每条数据之间都间隔了1秒。

Got: hi
Got: from
Got: the
Got: thread

使用clone函数实现mpsc: multiple producer; single consumer

use std::thread;
use std::sync::mpsc;
use std::time::Duration;
fn main() {let (tx, rx) = mpsc::channel();//使用clone函数clone一个transmitterlet tx1 = mpsc::Sender::clone(&tx);thread::spawn(move || {let vals = vec![String::from("hi"),String::from("from"),String::from("the"),String::from("thread"),];for val in vals {tx.send(val).unwrap();thread::sleep(Duration::from_secs(1));}});thread::spawn(move || {let vals = vec![String::from("more"),String::from("messages"),String::from("for"),String::from("you"),];for val in vals {tx1.send(val).unwrap();thread::sleep(Duration::from_secs(1));}});for received in rx {println!("Got: {}", received);}
}

Got: hi
Got: more
Got: from
Got: messages
Got: the
Got: for
Got: you
Got: thread