cargo-q 0.2.0

use std::sync::mpsc::{self, Receiver, Sender};
use std::sync::{Arc, Mutex};
use std::thread::{self, JoinHandle};

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

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

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

impl ThreadPool {
    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 {
            if let Some(thread) = worker.thread.take() {
                thread.join().unwrap();
            }
        }
    }
}

impl Worker {
    fn new(id: usize, receiver: Arc<Mutex<Receiver<Job>>>) -> Worker {
        let thread = thread::spawn(move || loop {
            let message = receiver.lock().unwrap().recv();

            match message {
                Ok(job) => {
                    job();
                }
                Err(_) => {
                    break;
                }
            }
        });

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

#[cfg(test)]
mod tests {
    use super::*;
    use std::sync::atomic::{AtomicUsize, Ordering};
    use std::sync::Arc;
    use std::thread::sleep;
    use std::time::Duration;

    #[test]
    fn test_thread_pool_executes_jobs() {
        let counter = Arc::new(AtomicUsize::new(0));
        let runs = 10;

        {
            let pool = ThreadPool::new(2);
            for _ in 0..runs {
                let counter_clone = Arc::clone(&counter);
                pool.execute(move || {
                    sleep(Duration::from_millis(10)); // Small delay to ensure we're actually using threads
                    counter_clone.fetch_add(1, Ordering::SeqCst);
                });
            }
        }

        assert_eq!(counter.load(Ordering::SeqCst), runs);
    }
}