117 lines
3.2 KiB
Rust
117 lines
3.2 KiB
Rust
use std::{
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sync::{mpsc, Arc, Mutex},
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thread
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};
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pub struct ThreadPool {
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workers: Vec<Worker>,
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sender: Option<mpsc::Sender<Job>>,
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}
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// Box: pointer for heap allocation (smart pointer); dyn: unknown type to compile time
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type Job = Box<dyn FnOnce() + Send + 'static>;
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impl ThreadPool {
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/// Create a new ThreadPool.
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///
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/// The size is the number of threads in the pool.
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///
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/// # Panics
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///
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/// The `new` function will panic if the size is zero.
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pub fn new(size: usize) -> ThreadPool {
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assert!(size > 0);
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// create asynchronous channel with sender/receiver pair (for jobs!)
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let (sender, receiver) = mpsc::channel();
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// protect receiver with thread-safe shared (Arc) mutex to avoid multiple access
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let receiver = Arc::new(Mutex::new(receiver));
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// pre(!)allocate space for workers
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let mut workers = Vec::with_capacity(size);
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// initialize all workers...
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for id in 0..size {
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// create worker with unique id and pointer to the shared mutex
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workers.push(Worker::new(id, Arc::clone(&receiver)));
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}
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// set thread pool variables
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ThreadPool {
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workers,
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// Some --> enum variant (Option): indicates that sender may not exist (=be null)
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sender: Some(sender),
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}
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}
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pub fn execute<F>(&self, f: F)
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where
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// FnOnce() --> only callable once; Send --> transfer to another thread; 'static --> lifetime
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F: FnOnce() + Send + 'static,
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{
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let job = Box::new(f);
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// commit job to sender object --> pass to threads for execution
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self.sender.as_ref().unwrap().send(job).unwrap();
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}
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}
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impl Drop for ThreadPool {
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fn drop(&mut self) {
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// drop sender first
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drop(self.sender.take());
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// then drop workers
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for worker in &mut self.workers {
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println!("Shutting down worker {}", worker.id);
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// join worker thread
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if let Some(thread) = worker.thread.take() {
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thread.join().unwrap();
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}
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}
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}
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}
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struct Worker {
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id: usize,
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thread: Option<thread::JoinHandle<()>>,
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}
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impl Worker {
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/// Create a new Worker..
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///
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/// The id is a unique identifier.
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/// The receiver is a shared pointer to a receiver protected by Mutex.
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fn new(id: usize, receiver: Arc<Mutex<mpsc::Receiver<Job>>>) -> Worker {
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// spawn thread and enter infinite loop
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let thread = thread::spawn(move || loop {
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// lock mutex and wait for job
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let message = receiver.lock().unwrap().recv();
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match message {
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// normal operation --> execute job
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Ok(job) => {
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println!("Worker {id} got a job; executing.");
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job();
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}
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// exit gracefully when pool is closed --> recv will return error then
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Err(_) => {
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println!("Worker {id} disconnected; shutting down.");
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break;
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}
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}
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});
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Worker {
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id,
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thread: Some(thread),
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}
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}
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}
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