Rust 程式設計小專案：WebServer 05

視訊地址

頭條地址：https://www.ixigua.com/i680718929763709798...
B站地址：https://www.bilibili.com/video/BV177411m78...

github地址

https://github.com/anonymousGiga/web-serve...

單執行緒web server存在的問題

請求只能序列處理，也就是說當第一個連結處理完之前不會處理第二個連結。考慮如下例子：

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);                //睡眠一段時間，模擬處理時間很長
}

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

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

在瀏覽器中開啟兩個視窗，分別輸入127.0.0.1:8080，會發現在第一個處理完之前，第二個不會響應。

使用多執行緒來解決問題

解決方式

修改main函式程式碼：

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(())
}

從瀏覽器開啟兩個標籤，進行測試，可以發現第一個沒有處理完之前，第二個請求已經開始處理。

存在問題

當存在海量請求時，系統也會跟著建立海量的執行緒，最終造成系統崩潰。

使用執行緒池來解決問題

執行緒池

知識點

多執行緒、管道。

從主執行緒將任務傳送到管道，工作執行緒等待在管道的接收端，當收到任務時，進行處理。

實現

初步設計

• 定義ThreadPool結構

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

• 定義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--
      }
  }

• 下面我們考慮new函式，可能的實現是這樣

  pub fn new(size: usize) -> ThreadPool {
      assert!(size > 0);
      let mut threads = Vec::with_capacity(size);
      for _ in 0..size {
          //建立執行緒：
          //問題來了，建立執行緒的時候需要傳入閉包，也就是具體做的動作，
          //可是這個時候我們還沒有具體的任務，怎麼辦？
      }
  
      ThreadPool {
          threads
      }
  }

• execute函式

  //設計execute的函式，可以參考thread::spawn
  pub fn execute<F>(&self, f: F)
      where
          F: FnOnce() + Send + 'static
  {
  
  }

初步設計的問題總結：

主要是在建立執行緒池的new函式中，需要傳入具體的任務，可是此時還沒有具體的任務，如何解決？

解決執行緒建立的問題

• 重新定義ThreadPool結構體

  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中建立執行緒

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

傳送任務

• 進一步將ThreadPool結構設計為

  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,
          }
      }
  }

  此段程式碼錯誤，因為receiver要線上程間傳遞，但是是非執行緒安全的。因此應該使用Arc<Mutex>。重新撰寫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,
          }
      }
  }

• 實現execute方法

  type Job = Box<dyn FnOnce() + Send + 'static>;//修改Job為trait物件的類別名稱
  
  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();
      }
  }

完整的程式碼

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為trait物件的類別名稱

impl ThreadPool {
    pub fn new(size: usize) -> ThreadPool {
        assert!(size > 0);
        // let mut threads = Vec::with_capacity(size);
        // for _ in 0..size {
        //     //建立執行緒：
        //     //問題來了，建立執行緒的時候需要傳入閉包，也就是具體做的動作，
        //     //可是這個時候我們還沒有具體的任務，怎麼辦？
        // }

        // 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();
    }
}

main的Cargo.toml

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

存在的問題

執行緒池中的執行緒怎麼結束？

想知道如何解決這個問題，請關注令狐一衝，下回為您分解。

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