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<main>
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<h2 id="优雅停机与清理"><a class="header" href="#优雅停机与清理">优雅停机与清理</a></h2>
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<p><a href="https://github.com/rust-lang/book/blob/8aa0d003e6499d733d639de32d70f590efa48657/src/ch21-03-graceful-shutdown-and-cleanup.md">ch21-03-graceful-shutdown-and-cleanup.md</a></p>
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<p>示例 21-20 中的代码如我们所愿，借助线程池异步地响应请求。这里有一些关于 <code>workers</code>、<code>id</code> 和 <code>thread</code> 字段没有被直接使用的警告，这提醒了我们还有一些东西没有清理。当我们用不那么优雅的 <kbd>ctrl</kbd>-<kbd>c</kbd> 方式终止主线程时，其他所有线程也都会立刻停止，即便它们正处于处理请求的过程中。</p>
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<p>接下来，我们要实现 <code>Drop</code> trait，在其中对线程池里的每个线程调用 <code>join</code>，这样它们就能在关闭前完成手头正在处理的请求。然后，我们还会实现一种方式，通知这些线程停止接收新请求并关闭。为了观察这些代码的实际效果，我们会修改 server，让它在优雅停机之前只接受两个请求。</p>
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<p>这里有一点需要先注意：这一切都不会影响执行闭包的那部分代码，因此如果我们是在 async 运行时里使用线程池，这一节中的内容也完全相同。</p>
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<h3 id="为-threadpool-实现-drop-trait"><a class="header" href="#为-threadpool-实现-drop-trait">为 <code>ThreadPool</code> 实现 <code>Drop</code> Trait</a></h3>
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<p>现在开始为线程池实现 <code>Drop</code>。当线程池被丢弃时，应该 join 所有线程以确保它们完成其操作。示例 21-22 展示了 <code>Drop</code> 实现的第一次尝试；这些代码还不能够编译：</p>
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<p><span class="filename">文件名：src/lib.rs</span></p>
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<pre><code class="language-rust ignore does_not_compile"><span class="boring">use std::{
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</span><span class="boring"> sync::{Arc, Mutex, mpsc},
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|
</span><span class="boring"> thread,
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</span><span class="boring">};
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</span><span class="boring">
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</span><span class="boring">pub struct ThreadPool {
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|
</span><span class="boring"> workers: Vec<Worker>,
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|
</span><span class="boring"> sender: mpsc::Sender<Job>,
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|
</span><span class="boring">}
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|
</span><span class="boring">
|
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|
</span><span class="boring">type Job = Box<dyn FnOnce() + Send + 'static>;
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl ThreadPool {
|
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|
</span><span class="boring"> /// Create a new ThreadPool.
|
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</span><span class="boring"> ///
|
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|
</span><span class="boring"> /// The size is the number of threads in the pool.
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|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// # Panics
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The `new` function will panic if the size is zero.
|
|
|
</span><span class="boring"> pub fn new(size: usize) -> ThreadPool {
|
|
|
</span><span class="boring"> assert!(size > 0);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let (sender, receiver) = mpsc::channel();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let receiver = Arc::new(Mutex::new(receiver));
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let mut workers = Vec::with_capacity(size);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> for id in 0..size {
|
|
|
</span><span class="boring"> workers.push(Worker::new(id, Arc::clone(&receiver)));
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> ThreadPool { workers, sender }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> pub fn execute<F>(&self, f: F)
|
|
|
</span><span class="boring"> where
|
|
|
</span><span class="boring"> F: FnOnce() + Send + 'static,
|
|
|
</span><span class="boring"> {
|
|
|
</span><span class="boring"> let job = Box::new(f);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> self.sender.send(job).unwrap();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span>impl Drop for ThreadPool {
|
|
|
fn drop(&mut self) {
|
|
|
for worker in &mut self.workers {
|
|
|
println!("Shutting down worker {}", worker.id);
|
|
|
|
|
|
worker.thread.join().unwrap();
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">
|
|
|
</span><span class="boring">struct Worker {
|
|
|
</span><span class="boring"> id: usize,
|
|
|
</span><span class="boring"> thread: thread::JoinHandle<()>,
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl Worker {
|
|
|
</span><span class="boring"> fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
|
|
|
</span><span class="boring"> let thread = thread::spawn(move || {
|
|
|
</span><span class="boring"> loop {
|
|
|
</span><span class="boring"> let job = receiver.lock().unwrap().recv().unwrap();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> println!("Worker {id} got a job; executing.");
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> job();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring"> });
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> Worker { id, thread }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}</span></code></pre>
|
|
|
<p><span class="caption">示例 21-22: 当线程池离开作用域时 join 每个线程</span></p>
|
|
|
<p>这里首先遍历线程池中的每个 <code>worker</code>。之所以使用 <code>&mut</code>，是因为 <code>self</code> 是一个可变引用，而且我们还需要修改 <code>worker</code>。对于每个 <code>worker</code>，我们都会打印一条消息，说明该 <code>Worker</code> 实例正在关闭，然后对这个 <code>Worker</code> 实例中的线程调用 <code>join</code>。如果 <code>join</code> 调用失败，就用 <code>unwrap</code> 让 Rust panic，进入一种不够优雅的关闭方式。</p>
|
|
|
<pre><code class="language-console">$ cargo check
|
|
|
Checking hello v0.1.0 (file:///projects/hello)
|
|
|
error[E0507]: cannot move out of `worker.thread` which is behind a mutable reference
|
|
|
--> src/lib.rs:52:13
|
|
|
|
|
|
|
52 | 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`
|
|
|
--> /rustc/1159e78c4747b02ef996e55082b704c09b970588/library/std/src/thread/mod.rs:1921:17
|
|
|
|
|
|
For more information about this error, try `rustc --explain E0507`.
|
|
|
error: could not compile `hello` (lib) due to 1 previous error
|
|
|
</code></pre>
|
|
|
<p>这里的错误告诉我们不能调用 <code>join</code>，因为我们手里只有每个 <code>worker</code> 的可变借用，而 <code>join</code> 需要拿走其参数的所有权。要解决这个问题，我们需要把 <code>thread</code> 从拥有它的 <code>Worker</code> 实例中移出来，这样 <code>join</code> 才能消费这个线程。一种做法和示例 18-15 中类似：如果 <code>Worker</code> 存放的是 <code>Option<thread::JoinHandle<()>></code>，就可以在这个 <code>Option</code> 上调用 <code>take</code> 方法，把值从 <code>Some</code> 变体中移出来，并在原地留下一个 <code>None</code>。换句话说，正在运行的 <code>Worker</code> 会在 <code>thread</code> 字段中持有一个 <code>Some</code>，而当我们想清理这个 <code>Worker</code> 时，就把 <code>Some</code> 替换成 <code>None</code>，这样这个 <code>Worker</code> 就不再持有可运行的线程。</p>
|
|
|
<p>然而，这种情况<strong>只</strong>会在丢弃 <code>Worker</code> 时出现。相应地，我们必须在任何访问 <code>worker.thread</code> 时处理 <code>Option<thread::JoinHandle<()>></code>。在惯用的 Rust 代码中 <code>Option</code> 用的很多，但当你发现自己总是知道 <code>Option</code> 中一定会有值，却还要将其包装在 <code>Option</code> 中来应对这一场景时，就应该考虑其他更优雅的方法了。</p>
|
|
|
<p>在这个例子中，存在一个更好的替代方案：<code>Vec::drain</code> 方法。它接受一个 range 参数来指定哪些项要从 <code>Vec</code> 中移除，并返回一个这些项的迭代器。使用 <code>..</code> range 语法会从 <code>Vec</code> 中移除<strong>所有</strong>值。</p>
|
|
|
<p>因此我们需要像下面这样更新 <code>ThreadPool</code> 的 <code>drop</code> 实现：</p>
|
|
|
<p><span class="filename">文件名：src/lib.rs</span></p>
|
|
|
<pre class="playground"><code class="language-rust edition2024"><span class="boring">#![allow(unused)]
|
|
|
</span><span class="boring">fn main() {
|
|
|
</span><span class="boring">use std::{
|
|
|
</span><span class="boring"> sync::{Arc, Mutex, mpsc},
|
|
|
</span><span class="boring"> thread,
|
|
|
</span><span class="boring">};
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">pub struct ThreadPool {
|
|
|
</span><span class="boring"> workers: Vec<Worker>,
|
|
|
</span><span class="boring"> sender: mpsc::Sender<Job>,
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">type Job = Box<dyn FnOnce() + Send + 'static>;
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl ThreadPool {
|
|
|
</span><span class="boring"> /// Create a new ThreadPool.
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The size is the number of threads in the pool.
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// # Panics
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The `new` function will panic if the size is zero.
|
|
|
</span><span class="boring"> pub fn new(size: usize) -> ThreadPool {
|
|
|
</span><span class="boring"> assert!(size > 0);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let (sender, receiver) = mpsc::channel();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let receiver = Arc::new(Mutex::new(receiver));
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let mut workers = Vec::with_capacity(size);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> for id in 0..size {
|
|
|
</span><span class="boring"> workers.push(Worker::new(id, Arc::clone(&receiver)));
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> ThreadPool { workers, sender }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> pub fn execute<F>(&self, f: F)
|
|
|
</span><span class="boring"> where
|
|
|
</span><span class="boring"> F: FnOnce() + Send + 'static,
|
|
|
</span><span class="boring"> {
|
|
|
</span><span class="boring"> let job = Box::new(f);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> self.sender.send(job).unwrap();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span>impl Drop for ThreadPool {
|
|
|
fn drop(&mut self) {
|
|
|
for worker in self.workers.drain(..) {
|
|
|
println!("Shutting down worker {}", worker.id);
|
|
|
|
|
|
worker.thread.join().unwrap();
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">
|
|
|
</span><span class="boring">struct Worker {
|
|
|
</span><span class="boring"> id: usize,
|
|
|
</span><span class="boring"> thread: thread::JoinHandle<()>,
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl Worker {
|
|
|
</span><span class="boring"> fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
|
|
|
</span><span class="boring"> let thread = thread::spawn(move || {
|
|
|
</span><span class="boring"> loop {
|
|
|
</span><span class="boring"> let job = receiver.lock().unwrap().recv().unwrap();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> println!("Worker {id} got a job; executing.");
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> job();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring"> });
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> Worker { id, thread }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">}</span></code></pre>
|
|
|
<p>这解决了编译器错误，而且不需要对我们的代码做任何其他修改。注意，因为 <code>drop</code> 可能在 panic 过程中被调用，这里的 <code>unwrap</code> 也可能再次 panic，造成双重 panic，并立刻让程序崩溃，中断正在进行的清理。对于示例程序来说这没问题，但在生产代码中并不推荐这样做。</p>
|
|
|
<h3 id="向线程发出信号让它们停止接收任务"><a class="header" href="#向线程发出信号让它们停止接收任务">向线程发出信号，让它们停止接收任务</a></h3>
|
|
|
<p>有了这些修改后，我们的代码已经可以无警告编译。然而坏消息是，它还不能按我们期望的方式工作。关键在于 <code>Worker</code> 实例中线程所运行的闭包逻辑：目前我们确实调用了 <code>join</code>，但这并不会让线程停止，因为它们会永远 <code>loop</code> 下去寻找新任务。如果用当前这个 <code>drop</code> 实现去丢弃 <code>ThreadPool</code>，主线程会永远阻塞，等待第一个线程结束。</p>
|
|
|
<p>为了修复这个问题，我们将修改 <code>ThreadPool</code> 的 <code>drop</code> 实现并修改 <code>Worker</code> 循环。</p>
|
|
|
<p>首先修改 <code>ThreadPool</code> 的 <code>drop</code> 实现在等待线程结束前显式地丢弃 <code>sender</code>。示例 21-23 展示了 <code>ThreadPool</code> 显式丢弃 <code>sender</code> 所作的修改。与处理线程时不同，这里<strong>确实</strong>需要使用 <code>Option</code>，以便能够使用 <code>Option::take</code> 将 <code>sender</code> 从 <code>ThreadPool</code> 中移出。</p>
|
|
|
<p><span class="filename">文件名：src/lib.rs</span></p>
|
|
|
<pre><code class="language-rust noplayground not_desired_behavior"><span class="boring">use std::{
|
|
|
</span><span class="boring"> sync::{Arc, Mutex, mpsc},
|
|
|
</span><span class="boring"> thread,
|
|
|
</span><span class="boring">};
|
|
|
</span><span class="boring">
|
|
|
</span>pub struct ThreadPool {
|
|
|
workers: Vec<Worker>,
|
|
|
sender: Option<mpsc::Sender<Job>>,
|
|
|
}
|
|
|
// --snip--
|
|
|
<span class="boring">
|
|
|
</span><span class="boring">type Job = Box<dyn FnOnce() + Send + 'static>;
|
|
|
</span><span class="boring">
|
|
|
</span>impl ThreadPool {
|
|
|
<span class="boring"> /// Create a new ThreadPool.
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The size is the number of threads in the pool.
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// # Panics
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The `new` function will panic if the size is zero.
|
|
|
</span> pub fn new(size: usize) -> ThreadPool {
|
|
|
// --snip--
|
|
|
|
|
|
<span class="boring"> assert!(size > 0);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let (sender, receiver) = mpsc::channel();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let receiver = Arc::new(Mutex::new(receiver));
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let mut workers = Vec::with_capacity(size);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> for id in 0..size {
|
|
|
</span><span class="boring"> workers.push(Worker::new(id, Arc::clone(&receiver)));
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span> ThreadPool {
|
|
|
workers,
|
|
|
sender: Some(sender),
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn execute<F>(&self, f: F)
|
|
|
where
|
|
|
F: FnOnce() + Send + 'static,
|
|
|
{
|
|
|
let job = Box::new(f);
|
|
|
|
|
|
self.sender.as_ref().unwrap().send(job).unwrap();
|
|
|
}
|
|
|
}
|
|
|
|
|
|
impl Drop for ThreadPool {
|
|
|
fn drop(&mut self) {
|
|
|
drop(self.sender.take());
|
|
|
|
|
|
for worker in self.workers.drain(..) {
|
|
|
println!("Shutting down worker {}", worker.id);
|
|
|
|
|
|
worker.thread.join().unwrap();
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
<span class="boring">
|
|
|
</span><span class="boring">struct Worker {
|
|
|
</span><span class="boring"> id: usize,
|
|
|
</span><span class="boring"> thread: thread::JoinHandle<()>,
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl Worker {
|
|
|
</span><span class="boring"> fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
|
|
|
</span><span class="boring"> let thread = thread::spawn(move || {
|
|
|
</span><span class="boring"> loop {
|
|
|
</span><span class="boring"> let job = receiver.lock().unwrap().recv().unwrap();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> println!("Worker {id} got a job; executing.");
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> job();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring"> });
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> Worker { id, thread }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}</span></code></pre>
|
|
|
<p><span class="caption">示例 21-23: 在 join <code>Worker</code> 线程之前显式丢弃 <code>sender</code></span></p>
|
|
|
<p>丢弃 <code>sender</code> 会关闭信道，这表明不会有更多的消息被发送。这时 <code>Worker</code> 实例中的无限循环中的所有 <code>recv</code> 调用都会返回错误。在示例 21-24 中，我们修改 <code>Worker</code> 循环在这种情况下优雅地退出，这意味着当 <code>ThreadPool</code> 的 <code>drop</code> 实现调用 <code>join</code> 时线程会结束。</p>
|
|
|
<p><span class="filename">文件名：src/lib.rs</span></p>
|
|
|
<pre><code class="language-rust noplayground"><span class="boring">use std::{
|
|
|
</span><span class="boring"> sync::{Arc, Mutex, mpsc},
|
|
|
</span><span class="boring"> thread,
|
|
|
</span><span class="boring">};
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">pub struct ThreadPool {
|
|
|
</span><span class="boring"> workers: Vec<Worker>,
|
|
|
</span><span class="boring"> sender: Option<mpsc::Sender<Job>>,
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">type Job = Box<dyn FnOnce() + Send + 'static>;
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl ThreadPool {
|
|
|
</span><span class="boring"> /// Create a new ThreadPool.
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The size is the number of threads in the pool.
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// # Panics
|
|
|
</span><span class="boring"> ///
|
|
|
</span><span class="boring"> /// The `new` function will panic if the size is zero.
|
|
|
</span><span class="boring"> pub fn new(size: usize) -> ThreadPool {
|
|
|
</span><span class="boring"> assert!(size > 0);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let (sender, receiver) = mpsc::channel();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let receiver = Arc::new(Mutex::new(receiver));
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let mut workers = Vec::with_capacity(size);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> for id in 0..size {
|
|
|
</span><span class="boring"> workers.push(Worker::new(id, Arc::clone(&receiver)));
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> ThreadPool {
|
|
|
</span><span class="boring"> workers,
|
|
|
</span><span class="boring"> sender: Some(sender),
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> pub fn execute<F>(&self, f: F)
|
|
|
</span><span class="boring"> where
|
|
|
</span><span class="boring"> F: FnOnce() + Send + 'static,
|
|
|
</span><span class="boring"> {
|
|
|
</span><span class="boring"> let job = Box::new(f);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> self.sender.as_ref().unwrap().send(job).unwrap();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">impl Drop for ThreadPool {
|
|
|
</span><span class="boring"> fn drop(&mut self) {
|
|
|
</span><span class="boring"> drop(self.sender.take());
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> for worker in self.workers.drain(..) {
|
|
|
</span><span class="boring"> println!("Shutting down worker {}", worker.id);
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> worker.thread.join().unwrap();
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring">struct Worker {
|
|
|
</span><span class="boring"> id: usize,
|
|
|
</span><span class="boring"> thread: thread::JoinHandle<()>,
|
|
|
</span><span class="boring">}
|
|
|
</span><span class="boring">
|
|
|
</span>impl Worker {
|
|
|
fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
|
|
|
let thread = thread::spawn(move || {
|
|
|
loop {
|
|
|
let message = receiver.lock().unwrap().recv();
|
|
|
|
|
|
match message {
|
|
|
Ok(job) => {
|
|
|
println!("Worker {id} got a job; executing.");
|
|
|
|
|
|
job();
|
|
|
}
|
|
|
Err(_) => {
|
|
|
println!("Worker {id} disconnected; shutting down.");
|
|
|
break;
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
});
|
|
|
|
|
|
Worker { id, thread }
|
|
|
}
|
|
|
}</code></pre>
|
|
|
<p><span class="caption">示例 21-24: 当 <code>recv</code> 返回错误时显式跳出循环</span></p>
|
|
|
<p>为了实践这些代码，如示例 21-25 所示修改 <code>main</code> 在优雅停机服务端之前只接受两个请求：</p>
|
|
|
<p><span class="filename">文件名：src/main.rs</span></p>
|
|
|
<pre><code class="language-rust ignore"><span class="boring">use hello::ThreadPool;
|
|
|
</span><span class="boring">use std::{
|
|
|
</span><span class="boring"> fs,
|
|
|
</span><span class="boring"> io::{BufReader, prelude::*},
|
|
|
</span><span class="boring"> net::{TcpListener, TcpStream},
|
|
|
</span><span class="boring"> thread,
|
|
|
</span><span class="boring"> time::Duration,
|
|
|
</span><span class="boring">};
|
|
|
</span><span class="boring">
|
|
|
</span>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.");
|
|
|
}
|
|
|
<span class="boring">
|
|
|
</span><span class="boring">fn handle_connection(mut stream: TcpStream) {
|
|
|
</span><span class="boring"> let buf_reader = BufReader::new(&stream);
|
|
|
</span><span class="boring"> let request_line = buf_reader.lines().next().unwrap().unwrap();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let (status_line, filename) = match &request_line[..] {
|
|
|
</span><span class="boring"> "GET / HTTP/1.1" => ("HTTP/1.1 200 OK", "hello.html"),
|
|
|
</span><span class="boring"> "GET /sleep HTTP/1.1" => {
|
|
|
</span><span class="boring"> thread::sleep(Duration::from_secs(5));
|
|
|
</span><span class="boring"> ("HTTP/1.1 200 OK", "hello.html")
|
|
|
</span><span class="boring"> }
|
|
|
</span><span class="boring"> _ => ("HTTP/1.1 404 NOT FOUND", "404.html"),
|
|
|
</span><span class="boring"> };
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let contents = fs::read_to_string(filename).unwrap();
|
|
|
</span><span class="boring"> let length = contents.len();
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> let response =
|
|
|
</span><span class="boring"> format!("{status_line}\r\nContent-Length: {length}\r\n\r\n{contents}");
|
|
|
</span><span class="boring">
|
|
|
</span><span class="boring"> stream.write_all(response.as_bytes()).unwrap();
|
|
|
</span><span class="boring">}</span></code></pre>
|
|
|
<p><span class="caption">示例 21-25: 在处理两个请求之后通过退出循环来停止服务端</span></p>
|
|
|
<p>你不会希望真实世界的 web 服务端只处理两次请求就停机了，这只是为了展示优雅停机和清理处于正常工作状态。</p>
|
|
|
<p><code>take</code> 方法定义在 <code>Iterator</code> trait 上，它会把迭代限制为至多前两个元素。<code>ThreadPool</code> 会在 <code>main</code> 结束时离开作用域，随后 <code>drop</code> 实现就会运行。</p>
|
|
|
<p>使用 <code>cargo run</code> 启动服务端，并发起三个请求。第三个请求应该会失败，而终端的输出应该看起来像这样：</p>
|
|
|
<pre><code class="language-console">$ cargo run
|
|
|
Compiling hello v0.1.0 (file:///projects/hello)
|
|
|
Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.41s
|
|
|
Running `target/debug/hello`
|
|
|
Worker 0 got a job; executing.
|
|
|
Shutting down.
|
|
|
Shutting down worker 0
|
|
|
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
|
|
|
</code></pre>
|
|
|
<p>你看到的 <code>Worker</code> ID 和打印消息顺序可能会有所不同。我们可以从这些消息中看出代码是如何工作的：<code>Worker</code> 实例 0 和 3 处理了前两个请求。server 在接收到第二个连接后就停止接受新连接，而 <code>ThreadPool</code> 上的 <code>Drop</code> 实现甚至会在 <code>Worker</code> 3 真正开始处理任务之前就开始执行。丢弃 <code>sender</code> 会让所有 <code>Worker</code> 实例断开连接，并通知它们关闭。每个 <code>Worker</code> 实例在断开时都会打印一条消息，然后线程池会调用 <code>join</code>，等待每个 <code>Worker</code> 线程结束。</p>
|
|
|
<p>注意这个具体执行过程里有个有意思的地方：<code>ThreadPool</code> 丢弃了 <code>sender</code> 之后，在任何一个 <code>Worker</code> 收到错误之前，就先尝试去 join <code>Worker</code> 0。此时 <code>Worker</code> 0 还没有从 <code>recv</code> 得到错误，所以主线程会阻塞，等待 <code>Worker</code> 0 结束。与此同时，<code>Worker</code> 3 收到了一个任务，然后所有线程都会收到错误。当 <code>Worker</code> 0 完成后，主线程再等待其余 <code>Worker</code> 实例结束。那时，它们都已经退出循环并停止了。</p>
|
|
|
<p>恭喜！现在我们完成了这个项目，也有了一个使用线程池异步响应请求的基础 web 服务端。我们能对服务端执行优雅停机，它会清理线程池中的所有线程。</p>
|
|
|
<p>如下是完整的代码参考：</p>
|
|
|
<p><span class="filename">文件名：src/main.rs</span></p>
|
|
|
<pre><code class="language-rust ignore">use hello::ThreadPool;
|
|
|
use std::{
|
|
|
fs,
|
|
|
io::{BufReader, prelude::*},
|
|
|
net::{TcpListener, TcpStream},
|
|
|
thread,
|
|
|
time::Duration,
|
|
|
};
|
|
|
|
|
|
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();
|
|
|
}</code></pre>
|
|
|
<p><span class="filename">文件名：src/lib.rs</span></p>
|
|
|
<pre><code class="language-rust noplayground">use std::{
|
|
|
sync::{Arc, Mutex, mpsc},
|
|
|
thread,
|
|
|
};
|
|
|
|
|
|
pub struct ThreadPool {
|
|
|
workers: Vec<Worker>,
|
|
|
sender: Option<mpsc::Sender<Job>>,
|
|
|
}
|
|
|
|
|
|
type Job = Box<dyn 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 receiver = Arc::new(Mutex::new(receiver));
|
|
|
|
|
|
let mut workers = Vec::with_capacity(size);
|
|
|
|
|
|
for id in 0..size {
|
|
|
workers.push(Worker::new(id, Arc::clone(&receiver)));
|
|
|
}
|
|
|
|
|
|
ThreadPool {
|
|
|
workers,
|
|
|
sender: Some(sender),
|
|
|
}
|
|
|
}
|
|
|
|
|
|
pub fn execute<F>(&self, f: F)
|
|
|
where
|
|
|
F: FnOnce() + Send + 'static,
|
|
|
{
|
|
|
let job = Box::new(f);
|
|
|
|
|
|
self.sender.as_ref().unwrap().send(job).unwrap();
|
|
|
}
|
|
|
}
|
|
|
|
|
|
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();
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
|
|
|
struct Worker {
|
|
|
id: usize,
|
|
|
thread: Option<thread::JoinHandle<()>>,
|
|
|
}
|
|
|
|
|
|
impl Worker {
|
|
|
fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
|
|
|
let thread = thread::spawn(move || {
|
|
|
loop {
|
|
|
let message = receiver.lock().unwrap().recv();
|
|
|
|
|
|
match message {
|
|
|
Ok(job) => {
|
|
|
println!("Worker {id} got a job; executing.");
|
|
|
|
|
|
job();
|
|
|
}
|
|
|
Err(_) => {
|
|
|
println!("Worker {id} disconnected; shutting down.");
|
|
|
break;
|
|
|
}
|
|
|
}
|
|
|
}
|
|
|
});
|
|
|
|
|
|
Worker {
|
|
|
id,
|
|
|
thread: Some(thread),
|
|
|
}
|
|
|
}
|
|
|
}</code></pre>
|
|
|
<p>我们还能做得更多！如果你希望继续增强这个项目，如下是一些点子：</p>
|
|
|
<ul>
|
|
|
<li>为 <code>ThreadPool</code> 和它的公有方法补充更多文档。</li>
|
|
|
<li>为这个库的功能添加测试。</li>
|
|
|
<li>把对 <code>unwrap</code> 的调用改成更健壮的错误处理。</li>
|
|
|
<li>用 <code>ThreadPool</code> 来执行除处理 web 请求之外的其他任务。</li>
|
|
|
<li>在 <a href="https://crates.io/">crates.io</a> 上找一个线程池 crate，用它实现一个类似的 web server，然后比较它的 API 和鲁棒性与我们实现的线程池有何不同。</li>
|
|
|
</ul>
|
|
|
<h2 id="总结"><a class="header" href="#总结">总结</a></h2>
|
|
|
<p>好极了！你已经完成了本书的学习！由衷感谢你与我们一道踏上这段 Rust 之旅。现在你已经准备好实现自己的 Rust 项目并帮助他人了。请不要忘记我们的社区，这里有其他 Rustaceans 正乐于帮助你迎接 Rust 之路上的任何挑战。</p>
|
|
|
|
|
|
</main>
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