用Rust实现一个多线程的web server

在本文之前，我们用Rust实现一个单线程的web server的例子，但是单线程的web server不够高效，所以本篇文章就来实现一个多线程的例子。

单线程web server存在的问题

请求只能串行处理，也就是说当第一个连结处理完之前不会处理第二个连结。考虑如下例子：

use std::net::{TcpListener, TcpStream};
use std::io::{Read, Write};
use std::fs;
use std::{thread, time};

fn handle_client(mut stream: TcpStream) {
    let mut buffer = [0; 512];
    stream.read(&mut buffer).unwrap();
    let get = b"GET / HTTP/1.1\r\n";
    let (status_line, filename) = if buffer.starts_with(get) {
        ("HTTP/1.1 200 OK\r\n\r\n", "main.html")
    } else {
        ("HTTP/1.1 404 NOT FOUND\r\n\r\n", "404.html")
    };

    let contents = fs::read_to_string(filename).unwrap();
    let response = format!("{}{}", status_line, contents);

    stream.write(response.as_bytes()).unwrap();
    stream.flush().unwrap();
    
    let ten_millis = time::Duration::from_millis(10000); 
    thread::sleep(ten_millis);				//睡眠一段时间，模拟处理时间很长
}

fn main() -> std::io::Result<()> {
    let listener = TcpListener::bind("127.0.0.1:8080")? ;

    for stream in listener.incoming() {
        handle_client(stream?);
    }
    Ok(())
}

在浏览器中打开两个窗口，分别输入127.0.0.1:8080，会发现在第一个处理完之前，第二个不会响应。

使用多线程来解决问题

• 解决方式

修改main函数代码：

fn main() -> std::io::Result<()> {
    let listener = TcpListener::bind("127.0.0.1:8080")?;
    let mut thread_vec: Vec<thread::JoinHandle<()>> = Vec::new();

    for stream in listener.incoming() {
        // handle_client(stream?);
        let stream = stream.unwrap();
        let handle = thread::spawn(|| {
            handle_client(stream);
        });
        thread_vec.push(handle);
    }

    for handle in thread_vec {
        handle.join().unwrap();
    }
    
    Ok(())
}

从浏览器打开两个标签，进行测试，可以发现第一个没有处理完之前，第二个请求已经开始处理。

• 存在问题

当存在海量请求时，系统也会跟着创建海量的线程，最终造成系统崩溃。

使用线程池来解决问题

• 线程池

• 知识点

多线程、管道。

从主线程将任务发送到管道，工作线程等待在管道的接收端，当收到任务时，进行处理。

线程池方式实现

1、初步设计

• 定义ThreadPool结构

use std::thread;
pub struct ThreadPool {
				thread: Vec<thread::JoinHandle<()>>,
}

• 定义ThreadPool的方法

impl ThreadPool {
	pub fn new(size: usize) -> ThreadPool {
		//--snip--
	}
	
	pub fn execute()
	//pub fn execute<F>(&self, f: F)
    //    where
    //        F: FnOnce() + Send + 'static
    {
		//--snip--
    }
}

• 下面我们考虑new函数，可能的实现是这样

pub fn new(size: usize) -> ThreadPool {
	assert!(size > 0);
	let mut threads = Vec::with_capacity(size);
	for _ in 0..size {
		//创建线程：
		//问题来了，创建线程的时候需要传入闭包，也就是具体做的动作，
		//可是这个时候我们还没有具体的任务，怎么办？
	}
		
	ThreadPool {
		threads
	}
}

• execute函数

//设计execute的函数，可以参考thread::spawn
pub fn execute<F>(&self, f: F)
    where
        F: FnOnce() + Send + 'static
{

}

初步设计的问题总结：

主要是在创建线程池的new函数中，需要传入具体的任务，可是此时还没有具体的任务，如何解决？

2、解决线程创建的问题

• 重新定义ThreadPool结构体

pub struct ThreadPool {
    workers: Vec<Worker>,
}

• ThreadPool的new方法

pub fn new(size: usize) -> ThreadPool {
    assert!(size > 0);

    let mut workers = Vec::with_capacity(size);

    for id in 0..size {
        workers.push(Worker::new(id));
    }

    ThreadPool {
        workers
    }
}

• 在worker中创建线程

struct Worker {
    id: usize,
    thread: thread::JoinHandle<()>,
}

impl Worker {
    fn new(id: usize) -> Worker {
        let thread = thread::spawn(|| {});

        Worker {
            id,
            thread,
        }
    }
}

3、发送任务

• 进一步将ThreadPool结构设计为

use std::sync::mpsc;

pub struct ThreadPool {
    workers: Vec<Worker>,
    sender: mpsc::Sender<Job>,
}

struct Job;

• 完善new方法

impl ThreadPool {
    // --snip--
    pub fn new(size: usize) -> ThreadPool {
        assert!(size > 0);

        let (sender, receiver) = mpsc::channel();//add
        let mut workers = Vec::with_capacity(size);

        for id in 0..size {
            //workers.push(Worker::new(id));
            workers.push(Worker::new(id, receiver));
        }

        ThreadPool {
            workers,
            sender,//add
        }
    }
    // --snip--
}

//--snip--

impl Worker {
    fn new(id: usize, receiver: mpsc::Receiver<Job>) -> Worker {
        let thread = thread::spawn(|| {
            receiver;
        });

        Worker {
            id,
            thread,
        }
    }
}

此段代码错误，因为receiver要在线程间传递，但是是非线程安全的。因此应该使用Arc<Mutex<T>>。重新撰写new方法如下：

use std::sync::Arc;
use std::sync::Mutex;
// --snip--

impl ThreadPool {
    // --snip--
    pub fn new(size: usize) -> ThreadPool {
        assert!(size > 0);

        let (sender, receiver) = mpsc::channel();

        let receiver = Arc::new(Mutex::new(receiver));//add

        let mut workers = Vec::with_capacity(size);

        for id in 0..size {
            workers.push(Worker::new(id, Arc::clone(&receiver)));
        }

        ThreadPool {
            workers,
            sender,
        }
    }

    // --snip--
}

impl Worker {
    fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
        let thread = thread::spawn(move || {
            loop {
                let job = receiver.lock().unwrap().recv().unwrap();

                println!("Worker {} got a job; executing.", id);

                job();
            }
        });

        Worker {
            id,
            thread,
        }
    }
}

• 实现execute方法

type Job = Box<dyn FnOnce() + Send + 'static>;//修改Job为trait对象的类别名称

impl ThreadPool {
    // --snip--

    pub fn execute<F>(&self, f: F)
        where
            F: FnOnce() + Send + 'static
    {
        let job = Box::new(f);

        self.sender.send(job).unwrap();
    }
}

完整代码

src/main.rs

use std::fs;
use std::io::{Read, Write};
use std::net::{TcpListener, TcpStream};
use std::{thread, time};
use mylib::ThreadPool;

fn handle_client(mut stream: TcpStream) {
    let mut buffer = [0; 512];
    stream.read(&mut buffer).unwrap();
    let get = b"GET / HTTP/1.1\r\n";
    let (status_line, filename) = if buffer.starts_with(get) {
        ("HTTP/1.1 200 OK\r\n\r\n", "main.html")
    } else {
        ("HTTP/1.1 404 NOT FOUND\r\n\r\n", "404.html")
    };

    let contents = fs::read_to_string(filename).unwrap();
    let response = format!("{}{}", status_line, contents);

    stream.write(response.as_bytes()).unwrap();
    stream.flush().unwrap();

    let ten_millis = time::Duration::from_millis(10000);
    thread::sleep(ten_millis);
}

fn main() -> std::io::Result<()> {
    let listener = TcpListener::bind("127.0.0.1:8080")?;
    // let mut thread_vec: Vec<thread::JoinHandle<()>> = Vec::new();

    let pool = ThreadPool::new(4);


    for stream in listener.incoming() {
        // // handle_client(stream?);
        let stream = stream.unwrap();
        // let handle = thread::spawn(|| {
        //     handle_client(stream);
        // });
        // thread_vec.push(handle);

        pool.execute(|| {
            handle_client(stream);
        });
    }

    // for handle in thread_vec {
    //     handle.join().unwrap();
    // }
    
    Ok(())
}

src/mylib/lib.rs

use std::thread;
use std::sync::mpsc;
use std::sync::Arc;
use std::sync::Mutex;

struct Worker {
    id: usize,
    thread: thread::JoinHandle<()>,
}

impl Worker {
    // fn new(id: usize) -> Worker {
    //     let thread = thread::spawn(|| {});

    //     Worker {
    //         id,
    //         thread,
    //     }
    // }

    // fn new(id: usize, receiver: mpsc::Receiver<Job>) -> Worker {
    //     let thread = thread::spawn(|| {
    //         receiver;
    //     });

    //     Worker {
    //         id,
    //         thread,
    //     }
    // }

    fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
        let thread = thread::spawn(move || {
            loop {
                let job = receiver.lock().unwrap().recv().unwrap();

                println!("Worker {} got a job; executing.", id);

                job();
            }
        });

        Worker {
            id,
            thread,
        }
    }
}

pub struct ThreadPool {
    workers: Vec<Worker>,
    sender: mpsc::Sender<Job>,
}

// struct Job;
type Job = Box<dyn FnOnce() + Send + 'static>;//修改Job为trait对象的类别名称

impl ThreadPool {
	pub fn new(size: usize) -> ThreadPool {
        assert!(size > 0);
        // let mut threads = Vec::with_capacity(size);
        // for _ in 0..size {
        //     //创建线程：
        //     //问题来了，创建线程的时候需要传入闭包，也就是具体做的动作，
        //     //可是这个时候我们还没有具体的任务，怎么办？
        // }
            
        // ThreadPool {
        //     threads
        // }

        let (sender, receiver) = mpsc::channel();
        let receiver = Arc::new(Mutex::new(receiver));
        let mut workers = Vec::with_capacity(size);
    
        for id in 0..size {
            //workers.push(Worker::new(id));
            //workers.push(Worker::new(id, receiver));
            workers.push(Worker::new(id, Arc::clone(&receiver)));
        }
    
        ThreadPool {
            workers,
            sender,
        }
	}
	
    pub fn execute<F>(&self, f: F)
        where
            F: FnOnce() + Send + 'static
    {
        let job = Box::new(f);

        self.sender.send(job).unwrap();
    }
}

在main的Cargo.toml添加如下依赖：

[dependencies]
mylib = {path = "./mylib"}

当前版本存在的问题

线程池中的线程怎么结束？

想知道如何解决这个问题，请关注令狐一冲，下回为您分解。