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//! Task Aggregation helper utility
use futures::future::{BoxFuture, FutureExt};
use futures::stream::futures_unordered::FuturesUnordered;
use futures::stream::StreamExt;
use parking_lot::Mutex;
use std::sync::Arc;
use tokio::sync::Notify;
/// A "Driver" is a generic static future with no output.
pub type Driver = BoxFuture<'static, ()>;
struct TaskAggInner {
notify: Arc<Notify>,
driver_list: Vec<Driver>,
n_driver: bool,
d_count: usize,
}
/// Task Aggregation helper struct handle.
#[derive(Clone)]
pub struct TaskAgg(Arc<Mutex<TaskAggInner>>);
trait S: 'static + Send + Sync {}
impl S for TaskAgg {}
impl TaskAgg {
/// Construct a new Task Aggregation driver and handle.
pub fn new() -> (Driver, Self) {
let inner = Arc::new(Mutex::new(TaskAggInner {
notify: Arc::new(Notify::new()),
driver_list: Vec::new(),
n_driver: false,
d_count: 0,
}));
let driver = {
let inner = inner.clone();
async move {
let mut fu = FuturesUnordered::new();
let mut driver_list = Vec::new();
loop {
let cont = {
let mut lock = inner.lock();
if lock.d_count == 0 {
false
} else {
driver_list.append(&mut lock.driver_list);
if !lock.n_driver {
lock.n_driver = true;
let n = lock.notify.clone();
let inner = inner.clone();
driver_list.push(
async move {
n.notified().await;
let mut lock = inner.lock();
lock.n_driver = false;
}
.boxed(),
);
}
true
}
};
if cont {
for driver in driver_list.drain(..) {
fu.push(driver);
}
} else {
// d_count must be zero, we can break
break;
}
let _ = fu.next().await;
}
}
.boxed()
};
(driver, Self(inner))
}
/// Push a new driver task into this aggregation construct.
pub fn push(&self, f: Driver) {
let inner = self.0.clone();
let mut lock = self.0.lock();
lock.d_count += 1;
lock.driver_list.push(
async move {
f.await;
inner.lock().d_count -= 1;
}
.boxed(),
);
lock.notify.notify_waiters();
}
}
#[cfg(test)]
mod tests {
use super::*;
#[tokio::test(flavor = "multi_thread")]
async fn test_task_agg() {
let (s, r) = tokio::sync::oneshot::channel();
let (driver, agg) = TaskAgg::new();
let agg2 = agg.clone();
agg.push(
async move {
agg2.push(
async move {
println!("test");
s.send(()).unwrap();
}
.boxed(),
);
}
.boxed(),
);
driver.await;
r.await.unwrap();
}
}