Final Project: Building a Multithreaded Web Server

Example Code

```rust
use std::io::prelude::*;
use std::net::{TcpListener, TcpStream};
use std::thread;
use std::time::Duration;
use std::fs;
use std::sync::mpsc;
use std::sync::{Arc, Mutex};

// -- ThreadPool Implementation --

type Job = Box<dyn FnOnce() + Send + 'static>;

enum Message {
    NewJob(Job),
    Terminate,
}

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

impl ThreadPool {
    /// Create a new ThreadPool.
    /// The size is the number of threads in the pool.
    /// Panics if size is zero.
    fn new(size: usize) -> ThreadPool {
        assert!(size > 0);

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

        // The receiver needs to be shared and mutable between multiple workers.
        // Arc allows multiple ownership.
        // Mutex allows mutable access (locking) by one worker at a time.
        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 }
    }

    fn execute<F>(&self, f: F)
    where
        F: FnOnce() + Send + 'static,
    {
        let job = Box::new(f);
        self.sender.send(Message::NewJob(job)).unwrap();
    }
}

impl Drop for ThreadPool {
    fn drop(&mut self) {
        println!("Sending terminate message to all workers.");

        for _ in &self.workers {
            self.sender.send(Message::Terminate).unwrap();
        }

        println!("Shutting down all workers.");

        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<Message>>>) -> Worker {
        let thread = thread::spawn(move || loop {
            let message = receiver.lock().unwrap().recv().unwrap();

            match message {
                Message::NewJob(job) => {
                    println!("Worker {} got a job; executing.", id);
                    job();
                }
                Message::Terminate => {
                    println!("Worker {} was told to terminate.", id);
                    break;
                }
            }
        });

        Worker { id, thread: Some(thread) }
    }
}

// -- Web Server Logic --

fn main() {
    let listener = TcpListener::bind("127.0.0.1:7878").unwrap();
    println!("Server listening on 127.0.0.1:7878");

    let pool = ThreadPool::new(4); // Create a thread pool with 4 threads

    // Listen for incoming connections and handle them in the thread pool
    for stream in listener.incoming().take(2) {
        let stream = stream.unwrap();
        
        pool.execute(move || {
            handle_connection(stream);
        });
    }

    println!("Shutting down.");
}

fn handle_connection(mut stream: TcpStream) {
    let mut buffer = [0; 1024]; // A small buffer for incoming request data
    stream.read(&mut buffer).unwrap();

    // Convert buffer to a string for basic HTTP parsing
    let request = String::from_utf8_lossy(&buffer[..]);
    
    // Define simple routes
    let get_root = b"GET / HTTP/1.1\r\n";
    let get_sleep = b"GET /sleep HTTP/1.1\r\n";

    // Match the request to a route and prepare the response
    let (status_line, filename) = if request.starts_with(std::str::from_utf8(get_root).unwrap()) {
        ("HTTP/1.1 200 OK", "hello.html")
    } else if request.starts_with(std::str::from_utf8(get_sleep).unwrap()) {
        thread::sleep(Duration::from_secs(5)); // Simulate a slow request
        ("HTTP/1.1 200 OK", "hello.html")
    } else {
        ("HTTP/1.1 404 NOT FOUND", "404.html")
    };

    let contents = fs::read_to_string(filename).unwrap();
    let response = format!("{}\r\nContent-Length: {}\r\n\r\n{}",
        status_line,
        contents.len(),
        contents
    );

    // Send the response back to the client
    stream.write_all(response.as_bytes()).unwrap();
    stream.flush().unwrap();
}

/*
To run this example:
1. Create a new Rust project: `cargo new web_server_mt --bin`
2. Navigate into the directory: `cd web_server_mt`
3. Replace `src/main.rs` with the code above.
4. Create `hello.html` in the project root with some content (e.g., "<h1>Hello from Rust!</h1>").
5. Create `404.html` in the project root (e.g., "<h1>404 Not Found</h1>").
6. Run the server: `cargo run`
7. Open your browser and navigate to `http://127.0.0.1:7878` or `http://127.0.0.1:7878/sleep` (the server will only handle two requests then shut down due to `.take(2)` in the loop).
*/
```