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use crate::runtime::current;
use futures::future::Either;
use std::{future::Future, sync::Arc};
use tokio::{
runtime,
sync::{OwnedSemaphorePermit, Semaphore},
task::JoinHandle,
};
#[derive(Debug)]
pub struct TrySpawnError;
pub struct BoundedExecutor {
inner: runtime::Handle,
semaphore: Arc<Semaphore>,
}
impl BoundedExecutor {
pub fn new(executor: runtime::Handle, num_permits: usize) -> Self {
Self {
inner: executor,
semaphore: Arc::new(Semaphore::new(num_permits)),
}
}
pub fn from_current(num_permits: usize) -> Self {
Self::new(current(), num_permits)
}
pub fn can_spawn(&self) -> bool {
self.semaphore.available_permits() > 0
}
pub fn try_spawn<F>(&self, future: F) -> Result<JoinHandle<F::Output>, TrySpawnError>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
let permit = self.semaphore.clone().try_acquire_owned().map_err(|_| TrySpawnError)?;
let handle = self.do_spawn(permit, future);
Ok(handle)
}
pub async fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
let permit = self.semaphore.clone().acquire_owned().await;
self.do_spawn(permit, future)
}
fn do_spawn<F>(&self, permit: OwnedSemaphorePermit, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
self.inner.spawn(async move {
let ret = future.await;
drop(permit);
ret
})
}
}
pub struct OptionallyBoundedExecutor {
inner: Either<runtime::Handle, BoundedExecutor>,
}
impl OptionallyBoundedExecutor {
pub fn new(executor: runtime::Handle, num_permits: Option<usize>) -> Self {
Self {
inner: num_permits
.map(|n| Either::Right(BoundedExecutor::new(executor.clone(), n)))
.unwrap_or_else(|| Either::Left(executor)),
}
}
pub fn from_current(num_permits: Option<usize>) -> Self {
Self::new(current(), num_permits)
}
pub fn can_spawn(&self) -> bool {
match &self.inner {
Either::Left(_) => true,
Either::Right(exec) => exec.can_spawn(),
}
}
pub fn try_spawn<F>(&self, future: F) -> Result<JoinHandle<F::Output>, TrySpawnError>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
match &self.inner {
Either::Left(exec) => Ok(exec.spawn(future)),
Either::Right(exec) => exec.try_spawn(future),
}
}
pub async fn spawn<F>(&self, future: F) -> JoinHandle<F::Output>
where
F: Future + Send + 'static,
F::Output: Send + 'static,
{
match &self.inner {
Either::Left(exec) => exec.spawn(future),
Either::Right(exec) => exec.spawn(future).await,
}
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::runtime;
use std::{
sync::{
atomic::{AtomicBool, Ordering},
Arc,
},
time::Duration,
};
use tokio::time::delay_for;
#[runtime::test_basic]
async fn spawn() {
let flag = Arc::new(AtomicBool::new(false));
let flag_cloned = flag.clone();
let executor = BoundedExecutor::new(runtime::current(), 1);
let task1_fut = executor
.spawn(async move {
delay_for(Duration::from_millis(1)).await;
flag_cloned.store(true, Ordering::SeqCst);
})
.await;
let task2_fut = executor
.spawn(async move {
assert_eq!(flag.load(Ordering::SeqCst), true);
})
.await;
task2_fut.await.unwrap();
task1_fut.await.unwrap();
}
}