20.3 最后的项目Web服务器的优雅停机与清理20.3.0. 回顾在上一篇文章中我们完成了多线程 Web 服务器但仍然有一些可以改进之处。这篇文章我们就来完善代码。注意本文衔接于 20.2. 最后的项目多线程Web服务器。如果你想详细了解从零开始构建 Web 服务器的过程请阅读完第 20 章的所有文章。20.3.1. 为ThreadPool实现Droptrait当我们想要关闭服务器使用不太优雅的 Ctrl C 方法停止主线程时所有其他线程也会立即停止即使它们仍在处理请求。用于管理清理的 trait 是Droptrait。我们只需要在本地编写drop函数来覆盖默认实现让线程能够在关闭之前完成当前正在处理的工作。我们还需要某种方式来阻止线程接收新请求并为停机做好准备。让我们为ThreadPool实现Droptraitimpl Drop for ThreadPool { fn drop(mut self) { for worker in mut self.workers { println!(Shutting down worker {}, worker.id); worker.thread.join().unwrap(); } } }逻辑就是遍历每一个worker然后调用worker里thread字段的join方法详见 16.1. 使用多线程同时运行代码。运行cargo checkerror[E0507]: cannot move out of worker.thread which is behind a mutable reference -- src/lib.rs:42:13 | 42 | worker.thread.join().unwrap(); | ^^^^^^^^^^^^^ ------ worker.thread moved due to this method call | | | move occurs because worker.thread has type JoinHandle(), which does not implement the Copy trait | note: JoinHandle::T::join takes ownership of the receiver self, which moves worker.thread -- /Users/stanyin/.rustup/toolchains/stable-aarch64-apple-darwin/lib/rustlib/src/rust/library/std/src/thread/join_handle.rs:149:17 | 149 | pub fn join(self) - ResultT { | ^^^^ For more information about this error, try rustc --explain E0507. error: could not compile web_server (lib) due to 1 previous error报错信息显示我们无法把worker的thread字段移出来因为我们只有每个worker的可变引用但join需要JoinHandle的所有权也就是worker.thread的所有权。为了满足所有权要求我们需要修改Worker中thread字段的类型用OptionT包裹thread::JoinHandle()。这样我们就可以调用OptionT::take来获得所有权struct Worker { id: usize, thread: Optionthread::JoinHandle(), }凡是使用了thread字段的地方也都必须因OptionT而更新impl Worker { fn new(id: usize, receiver: ArcMutexmpsc::ReceiverJob) - 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: Some(thread), } } }把thread字段的值从thread改为Some(thread)。impl Drop for ThreadPool { fn drop(mut self) { for worker in mut self.workers { println!(Shutting down worker {}, worker.id); if let Some(thread) worker.thread.take() { thread.join().unwrap(); } } } }使用if let模式匹配在worker.thread为Some时取出其中的值使用take可以获得所有权而不是可变引用。20.3.2. 向线程发出信号以退出这样修改后可以编译通过但仍未达到预期效果。调用drop并不会真正关停线程因为线程仍然卡在loop中等待工作。如果用这个drop方法丢弃ThreadPool主线程会永远阻塞等待第一个线程结束因为每个线程都一直在循环寻找工作不会跳出循环。我们需要ThreadPool的sender字段有两种状态一种是附带任务的存活状态另一种是终止状态pub struct ThreadPool { workers: VecWorker, sender: Optionmpsc::SenderJob, }使用OptionT可以让它表示这两种状态。凡是使用了sender字段的地方也都必须修改impl Drop for ThreadPool { fn drop(mut self) { drop(self.sender.take()); for worker in mut self.workers { println!(Shutting down worker {}, worker.id); if let Some(thread) worker.thread.take() { thread.join().unwrap(); } } } }添加drop(self.sender.take());来显式丢弃发送端这样就会关闭通道。发生这种情况时worker 无限循环中执行的所有recv调用都会返回错误worker 也会停止运行。pub fn new(size: usize) - ThreadPool { assert!(size 0); let (sender, receiver) mpsc::channel(); let mut workers Vec::with_capacity(size); let receiver Arc::new(Mutex::new(receiver)); for id in 0..size { workers.push(Worker::new(id, Arc::clone(receiver))); } ThreadPool { workers, sender: Some(sender), } }用Some包裹返回值中的sender字段。pub fn executeF(self, f: F) where F: FnOnce() Send static, { let job Box::new(f); self.sender.as_ref().unwrap().send(job).unwrap(); }因为sender现在是Option我们调用as_ref得到OptionSender对内部发送端的引用而不会把它从self中移出。随后再unwrap并调用sendsend在发送端上接受self并把任务移入通道。这样改仍然不够优雅因为 worker 无限循环中执行的所有recv调用都会返回错误。最好不要因为错误而退出所以还需要再改一处fn new(id: usize, receiver: ArcMutexmpsc::ReceiverJob) - Worker { let thread thread::spawn(move || loop { let job receiver.lock().unwrap().recv(); match job { Ok(job) { println!(Worker {} got a job; executing., id); job(); } Err(_) { println!(Worker {} disconnected; shutting down., id); break; } } });去掉job上最后一个unwrap转而使用match分支Ok变体就执行jobErr变体则打印 worker 正在断开连接然后跳出循环。20.3.3. 试运行为了测试修改后的行为我们修改main.rs让服务器只接受两个请求通过take限制迭代次数fn main() { let listener TcpListener::bind(127.0.0.1:7878).unwrap(); let pool ThreadPool::new(4); for stream in listener.incoming().take(2) { let stream stream.unwrap(); pool.execute(|| { handle_connection(stream); }); } println!(Shutting down.); }控制台输出如下某次可能的运行结果任务分配与交错顺序是不确定的Shutting down. Shutting down worker 0 Worker 0 got a job; executing. Worker 3 got a job; executing. Worker 1 disconnected; shutting down. Worker 2 disconnected; shutting down. Worker 3 disconnected; shutting down. Worker 0 disconnected; shutting down. Shutting down worker 1 Shutting down worker 2 Shutting down worker 3你可能会看到不同的 Worker id以及 “got a job”“disconnected”“Shutting down worker” 行的不同交错顺序但整体模式应该类似。20.3.4. 总结main.rs:use std::{ fs, io::{prelude::*, BufReader}, net::{TcpListener, TcpStream}, thread, time::Duration, }; use web_server::ThreadPool; fn main() { let listener TcpListener::bind(127.0.0.1:7878).unwrap(); let pool ThreadPool::new(4); for stream in listener.incoming().take(2) { let stream stream.unwrap(); pool.execute(|| { handle_connection(stream); }); } println!(Shutting down.); } fn handle_connection(mut stream: TcpStream) { let buf_reader BufReader::new(stream); let request_line buf_reader.lines().next().unwrap().unwrap(); let (status_line, filename) match request_line[..] { GET / HTTP/1.1 (HTTP/1.1 200 OK, hello.html), GET /sleep HTTP/1.1 { thread::sleep(Duration::from_secs(5)); (HTTP/1.1 200 OK, hello.html) } _ (HTTP/1.1 404 NOT FOUND, 404.html), }; let contents fs::read_to_string(filename).unwrap(); let length contents.len(); let response format!({status_line}\r\nContent-Length: {length}\r\n\r\n{contents}); stream.write_all(response.as_bytes()).unwrap(); }lib.rs:use std::{ sync::{mpsc, Arc, Mutex}, thread, }; pub struct ThreadPool { workers: VecWorker, sender: Optionmpsc::SenderJob, } impl Drop for ThreadPool { fn drop(mut self) { drop(self.sender.take()); for worker in mut self.workers { println!(Shutting down worker {}, worker.id); if let Some(thread) worker.thread.take() { thread.join().unwrap(); } } } } type Job Boxdyn FnOnce() Send static; impl ThreadPool { /// Create a new ThreadPool. /// /// The size is the number of threads in the pool. /// /// # Panics /// /// The new function will panic if the size is zero. pub fn new(size: usize) - ThreadPool { assert!(size 0); let (sender, receiver) mpsc::channel(); let mut workers Vec::with_capacity(size); let receiver Arc::new(Mutex::new(receiver)); for id in 0..size { workers.push(Worker::new(id, Arc::clone(receiver))); } ThreadPool { workers, sender: Some(sender), } } pub fn executeF(self, f: F) where F: FnOnce() Send static, { let job Box::new(f); self.sender.as_ref().unwrap().send(job).unwrap(); } } struct Worker { id: usize, thread: Optionthread::JoinHandle(), } impl Worker { fn new(id: usize, receiver: ArcMutexmpsc::ReceiverJob) - Worker { let thread thread::spawn(move || loop { let job receiver.lock().unwrap().recv(); match job { Ok(job) { println!(Worker {} got a job; executing., id); job(); } Err(_) { println!(Worker {} disconnected; shutting down., id); break; } } }); Worker { id, thread: Some(thread), } } }hello.html:!DOCTYPE html html langen head meta charsetutf-8 titleHello!/title /head body h1Hello!/h1 pHi from Rust/p /body /html404.html:!DOCTYPE html html langen head meta charsetutf-8 titleHello!/title /head body h1Oops!/h1 pSorry, I dont know what youre asking for./p /body /html