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use core::future::Future;
use std::pin::Pin;
use std::sync::Mutex;
use futures::future::join_all;
use futures::select;
use futures_util::future::*;
use std::sync::Arc;
use tokio::sync::{mpsc, watch, Notify};
use crate::error::Error;
type JobOutput = Result<(), Error>;
type Job = Pin<Box<dyn Future<Output = JobOutput> + Send>>;
pub struct BackgroundRunner {
n_runners: usize,
pub stop_signal: watch::Receiver<bool>,
queue_in: mpsc::UnboundedSender<(Job, bool)>,
queue_out: Mutex<mpsc::UnboundedReceiver<(Job, bool)>>,
job_notify: Notify,
workers: Mutex<Vec<tokio::task::JoinHandle<()>>>,
}
impl BackgroundRunner {
pub fn new(n_runners: usize, stop_signal: watch::Receiver<bool>) -> Arc<Self> {
let (queue_in, queue_out) = mpsc::unbounded_channel();
Arc::new(Self {
n_runners,
stop_signal,
queue_in,
queue_out: Mutex::new(queue_out),
job_notify: Notify::new(),
workers: Mutex::new(Vec::new()),
})
}
pub async fn run(self: Arc<Self>) {
let mut workers = self.workers.lock().unwrap();
for i in 0..self.n_runners {
workers.push(tokio::spawn(self.clone().runner(i)));
}
drop(workers);
let mut stop_signal = self.stop_signal.clone();
while let Some(exit_now) = stop_signal.recv().await {
if exit_now {
let mut workers = self.workers.lock().unwrap();
let workers_vec = workers.drain(..).collect::<Vec<_>>();
join_all(workers_vec).await;
return;
}
}
}
pub fn spawn<T>(&self, job: T)
where
T: Future<Output = JobOutput> + Send + 'static,
{
let boxed: Job = Box::pin(job);
let _: Result<_, _> = self.queue_in.clone().send((boxed, false));
self.job_notify.notify();
}
pub fn spawn_cancellable<T>(&self, job: T)
where
T: Future<Output = JobOutput> + Send + 'static,
{
let boxed: Job = Box::pin(job);
let _: Result<_, _> = self.queue_in.clone().send((boxed, true));
self.job_notify.notify();
}
pub fn spawn_worker<F, T>(&self, name: String, worker: F)
where
F: FnOnce(watch::Receiver<bool>) -> T + Send + 'static,
T: Future<Output = ()> + Send + 'static,
{
let mut workers = self.workers.lock().unwrap();
let stop_signal = self.stop_signal.clone();
workers.push(tokio::spawn(async move {
worker(stop_signal).await;
info!("Worker exited: {}", name);
}));
}
async fn runner(self: Arc<Self>, i: usize) {
let mut stop_signal = self.stop_signal.clone();
loop {
let must_exit: bool = *stop_signal.borrow();
if let Some(job) = self.dequeue_job(must_exit) {
if let Err(e) = job.await {
error!("Job failed: {}", e)
}
} else {
if must_exit {
info!("Background runner {} exiting", i);
return;
}
select! {
_ = self.job_notify.notified().fuse() => (),
_ = stop_signal.recv().fuse() => (),
}
}
}
}
fn dequeue_job(&self, must_exit: bool) -> Option<Job> {
let mut queue = self.queue_out.lock().unwrap();
while let Ok((job, cancellable)) = queue.try_recv() {
if cancellable && must_exit {
continue;
} else {
return Some(job);
}
}
None
}
}
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