scratch-server 1.0.1

use std::{
    fmt,
    sync::{mpsc, Arc, Mutex},
    thread,
};

#[derive(Debug)]
pub struct PoolCreationError;

impl fmt::Display for PoolCreationError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(
            f,
            "Failed to create thread pool: size must be greater than 0"
        )
    }
}

impl std::error::Error for PoolCreationError {}

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

impl ThreadPool {
    pub fn build(size: usize) -> Result<ThreadPool, PoolCreationError> {
        if size == 0 {
            return Err(PoolCreationError);
        }
        let mut workers = Vec::with_capacity(size);

        let (sender, receiver) = mpsc::channel();
        let receiver = Arc::new(Mutex::new(receiver));

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

        Ok(ThreadPool {
            workers,
            sender: Some(sender),
        })
    }

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

        self.sender.as_ref().unwrap().send(job)?;
        Ok(())
    }
}

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

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

impl Worker {
    pub 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) => {
                    job();
                }
                Err(_) => {
                    println!("Worker {id} disconnected; shutting down.");
                    break;
                }
            }
        });

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