smol-rs
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async-executor
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Make executors scoped

This commit is contained in:
Stjepan Glavina 2020-09-19 22:38:11 +02:00
parent 19eb3ccd6e
commit 6f2b0b8a49
4 changed files with 127 additions and 193 deletions
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3
Cargo.toml
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@ -13,11 +13,12 @@ categories = ["asynchronous", "concurrency"]
readme = "README.md"
[dependencies]
async-task = "3.0.0"
async-task = { path = "../async-task" }
concurrent-queue = "1.2.2"
fastrand = "1.3.4"
futures-lite = "1.0.0"
once_cell = "1.4.1"
vec-arena = "1.0.0"
[dev-dependencies]
async-channel = "1.4.1"

14
examples/priority.rs
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@ -18,23 +18,23 @@ enum Priority {
/// An executor with task priorities.
///
/// Tasks with lower priorities only get polled when there are no tasks with higher priorities.
struct PriorityExecutor {
ex: [Executor; 3],
struct PriorityExecutor<'a> {
ex: [Executor<'a>; 3],
}
impl PriorityExecutor {
impl<'a> PriorityExecutor<'a> {
/// Creates a new executor.
const fn new() -> PriorityExecutor {
const fn new() -> PriorityExecutor<'a> {
PriorityExecutor {
ex: [Executor::new(), Executor::new(), Executor::new()],
}
}
/// Spawns a task with the given priority.
fn spawn<T: Send + 'static>(
fn spawn<T: Send + 'a>(
&self,
priority: Priority,
future: impl Future<Output = T> + Send + 'static,
future: impl Future<Output = T> + Send + 'a,
) -> Task<T> {
self.ex[priority as usize].spawn(future)
}
@ -59,7 +59,7 @@ impl PriorityExecutor {
}
fn main() {
static EX: PriorityExecutor = PriorityExecutor::new();
static EX: PriorityExecutor<'_> = PriorityExecutor::new();
// Spawn a thread running the executor forever.
thread::spawn(|| future::block_on(EX.run()));

257
src/lib.rs
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@ -18,160 +18,23 @@
//! future::block_on(ex.run(task));
//! ```
#![forbid(unsafe_code)]
#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
use std::future::Future;
use std::marker::PhantomData;
use std::panic::{RefUnwindSafe, UnwindSafe};
use std::pin::Pin;
use std::rc::Rc;
use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
use std::sync::{Arc, Mutex, RwLock};
use std::task::{Context, Poll, Waker};
use std::task::{Poll, Waker};
use async_task::Runnable;
use concurrent_queue::ConcurrentQueue;
use futures_lite::{future, FutureExt};
use vec_arena::Arena;
/// A runnable future, ready for execution.
///
/// When a future is internally spawned using `async_task::spawn()` or `async_task::spawn_local()`,
/// we get back two values:
///
/// 1. an `async_task::Task<()>`, which we refer to as a `Runnable`
/// 2. an `async_task::JoinHandle<T, ()>`, which is wrapped inside a `Task<T>`
///
/// Once a `Runnable` is run, it "vanishes" and only reappears when its future is woken. When it's
/// woken up, its schedule function is called, which means the `Runnable` gets pushed into a task
/// queue in an executor.
type Runnable = async_task::Task<()>;
/// A spawned future.
///
/// Tasks are also futures themselves and yield the output of the spawned future.
///
/// When a task is dropped, its gets canceled and won't be polled again. To cancel a task a bit
/// more gracefully and wait until it stops running, use the [`cancel()`][Task::cancel()] method.
///
/// Tasks that panic get immediately canceled. Awaiting a canceled task also causes a panic.
///
/// If a task panics, the panic will be thrown into the [`Executor::run()`] or
/// [`LocalExecutor::run()`] invocation that polled it.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
/// use futures_lite::future;
/// use std::thread;
///
/// let ex = Executor::new();
///
/// // Spawn a future onto the executor.
/// let task = ex.spawn(async {
/// println!("Hello from a task!");
/// 1 + 2
/// });
///
/// // Run an executor thread.
/// thread::spawn(move || future::block_on(ex.run(future::pending::<()>())));
///
/// // Wait for the result.
/// assert_eq!(future::block_on(task), 3);
/// ```
#[must_use = "tasks get canceled when dropped, use `.detach()` to run them in the background"]
#[derive(Debug)]
pub struct Task<T>(Option<async_task::JoinHandle<T, ()>>);
impl<T> UnwindSafe for Task<T> {}
impl<T> RefUnwindSafe for Task<T> {}
impl<T> Task<T> {
/// Detaches the task to let it keep running in the background.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
/// use async_io::Timer;
/// use std::time::Duration;
///
/// let ex = Executor::new();
///
/// // Spawn a deamon future.
/// ex.spawn(async {
/// loop {
/// println!("I'm a daemon task looping forever.");
/// Timer::after(Duration::from_secs(1)).await;
/// }
/// })
/// .detach();
/// ```
pub fn detach(mut self) {
self.0.take().unwrap();
}
/// Cancels the task and waits for it to stop running.
///
/// Returns the task's output if it was completed just before it got canceled, or [`None`] if
/// it didn't complete.
///
/// While it's possible to simply drop the [`Task`] to cancel it, this is a cleaner way of
/// canceling because it also waits for the task to stop running.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
/// use async_io::Timer;
/// use futures_lite::future;
/// use std::thread;
/// use std::time::Duration;
///
/// let ex = Executor::new();
///
/// // Spawn a deamon future.
/// let task = ex.spawn(async {
/// loop {
/// println!("Even though I'm in an infinite loop, you can still cancel me!");
/// Timer::after(Duration::from_secs(1)).await;
/// }
/// });
///
/// // Run an executor thread.
/// thread::spawn(move || future::block_on(ex.run(future::pending::<()>())));
///
/// future::block_on(async {
/// Timer::after(Duration::from_secs(3)).await;
/// task.cancel().await;
/// });
/// ```
pub async fn cancel(self) -> Option<T> {
let mut task = self;
let handle = task.0.take().unwrap();
handle.cancel();
handle.await
}
}
impl<T> Drop for Task<T> {
fn drop(&mut self) {
if let Some(handle) = &self.0 {
handle.cancel();
}
}
}
impl<T> Future for Task<T> {
type Output = T;
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
match Pin::new(&mut self.0.as_mut().unwrap()).poll(cx) {
Poll::Pending => Poll::Pending,
Poll::Ready(output) => Poll::Ready(output.expect("task has failed")),
}
}
}
#[doc(no_inline)]
pub use async_task::Task;
/// The state of a executor.
#[derive(Debug)]
@ -187,6 +50,8 @@ struct State {
/// A list of sleeping tickers.
sleepers: Mutex<Sleepers>,
active: Mutex<Arena<Waker>>,
}
impl State {
@ -201,6 +66,7 @@ impl State {
wakers: Vec::new(),
free_ids: Vec::new(),
}),
active: Mutex::new(Arena::new()),
}
}
@ -321,14 +187,18 @@ impl Sleepers {
/// }));
/// ```
#[derive(Debug)]
pub struct Executor {
pub struct Executor<'a> {
state: once_cell::sync::OnceCell<Arc<State>>,
_marker: PhantomData<std::cell::UnsafeCell<&'a ()>>,
}
impl UnwindSafe for Executor {}
impl RefUnwindSafe for Executor {}
unsafe impl Send for Executor<'_> {}
unsafe impl Sync for Executor<'_> {}
impl Executor {
impl UnwindSafe for Executor<'_> {}
impl RefUnwindSafe for Executor<'_> {}
impl<'a> Executor<'a> {
/// Creates a new executor.
///
/// # Examples
@ -338,9 +208,10 @@ impl Executor {
///
/// let ex = Executor::new();
/// ```
pub const fn new() -> Executor {
pub const fn new() -> Executor<'a> {
Executor {
state: once_cell::sync::OnceCell::new(),
_marker: PhantomData,
}
}
@ -357,14 +228,8 @@ impl Executor {
/// println!("Hello world");
/// });
/// ```
pub fn spawn<T: Send + 'static>(
&self,
future: impl Future<Output = T> + Send + 'static,
) -> Task<T> {
// Create a task, push it into the queue by scheduling it, and return its `Task` handle.
let (runnable, handle) = async_task::spawn(future, self.schedule(), ());
runnable.schedule();
Task(Some(handle))
pub fn spawn<T: Send + 'a>(&self, future: impl Future<Output = T> + Send + 'a) -> Task<T> {
unsafe { self.spawn_unchecked(future) }
}
/// Attempts to run a task if at least one is scheduled.
@ -472,16 +337,42 @@ impl Executor {
fn state(&self) -> &Arc<State> {
self.state.get_or_init(|| Arc::new(State::new()))
}
}
impl Drop for Executor {
fn drop(&mut self) {
// TODO(stjepang): Cancel all remaining tasks.
unsafe fn spawn_unchecked<T>(&self, future: impl Future<Output = T>) -> Task<T> {
let mut active = self.state().active.lock().unwrap();
let index = active.next_vacant();
let state = self.state().clone();
let future = async move {
let _guard = CallOnDrop(move || drop(state.active.lock().unwrap().remove(index)));
future.await
};
let (runnable, task) = async_task::spawn_unchecked(future, self.schedule());
active.insert(runnable.waker());
runnable.schedule();
task
}
}
impl Default for Executor {
fn default() -> Executor {
impl Drop for Executor<'_> {
fn drop(&mut self) {
if let Some(state) = self.state.get() {
{
let mut state = state.active.lock().unwrap();
for i in 0..state.capacity() {
if let Some(w) = state.remove(i) {
w.wake();
}
}
}
while state.queue.pop().is_ok() {}
}
}
}
impl<'a> Default for Executor<'a> {
fn default() -> Executor<'a> {
Executor::new()
}
}
@ -750,18 +641,18 @@ fn steal<T>(src: &ConcurrentQueue<T>, dest: &ConcurrentQueue<T>) {
/// }));
/// ```
#[derive(Debug)]
pub struct LocalExecutor {
pub struct LocalExecutor<'a> {
/// The inner executor.
inner: once_cell::unsync::OnceCell<Executor>,
inner: once_cell::unsync::OnceCell<Executor<'a>>,
/// Make sure the type is `!Send` and `!Sync`.
_marker: PhantomData<Rc<()>>,
}
impl UnwindSafe for LocalExecutor {}
impl RefUnwindSafe for LocalExecutor {}
impl UnwindSafe for LocalExecutor<'_> {}
impl RefUnwindSafe for LocalExecutor<'_> {}
impl LocalExecutor {
impl<'a> LocalExecutor<'a> {
/// Creates a single-threaded executor.
///
/// # Examples
@ -771,7 +662,7 @@ impl LocalExecutor {
///
/// let local_ex = LocalExecutor::new();
/// ```
pub const fn new() -> LocalExecutor {
pub const fn new() -> LocalExecutor<'a> {
LocalExecutor {
inner: once_cell::unsync::OnceCell::new(),
_marker: PhantomData,
@ -791,11 +682,8 @@ impl LocalExecutor {
/// println!("Hello world");
/// });
/// ```
pub fn spawn<T: 'static>(&self, future: impl Future<Output = T> + 'static) -> Task<T> {
// Create a task, push it into the queue by scheduling it, and return its `Task` handle.
let (runnable, handle) = async_task::spawn_local(future, self.schedule(), ());
runnable.schedule();
Task(Some(handle))
pub fn spawn<T: 'a>(&self, future: impl Future<Output = T> + 'a) -> Task<T> {
unsafe { self.inner().spawn_unchecked(future) }
}
/// Attempts to run a task if at least one is scheduled.
@ -861,24 +749,23 @@ impl LocalExecutor {
self.inner().run(future).await
}
/// Returns a function that schedules a runnable task when it gets woken up.
fn schedule(&self) -> impl Fn(Runnable) + Send + Sync + 'static {
let state = self.inner().state().clone();
move |runnable| {
state.queue.push(runnable).unwrap();
state.notify();
}
}
/// Returns a reference to the inner executor.
fn inner(&self) -> &Executor {
fn inner(&self) -> &Executor<'a> {
self.inner.get_or_init(|| Executor::new())
}
}
impl Default for LocalExecutor {
fn default() -> LocalExecutor {
impl<'a> Default for LocalExecutor<'a> {
fn default() -> LocalExecutor<'a> {
LocalExecutor::new()
}
}
/// Runs a closure when dropped.
struct CallOnDrop<F: Fn()>(F);
impl<F: Fn()> Drop for CallOnDrop<F> {
fn drop(&mut self) {
(self.0)();
}
}

46
tests/drop.rs Normal file
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@ -0,0 +1,46 @@
use std::panic::catch_unwind;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::Mutex;
use std::task::{Poll, Waker};
use async_executor::Executor;
use futures_lite::future;
use once_cell::sync::Lazy;
#[test]
fn smoke() {
static DROP: AtomicUsize = AtomicUsize::new(0);
static WAKER: Lazy<Mutex<Option<Waker>>> = Lazy::new(|| Default::default());
let ex = Executor::new();
let task = ex.spawn(async {
let _guard = CallOnDrop(|| {
DROP.fetch_add(1, Ordering::SeqCst);
});
future::poll_fn(|cx| {
*WAKER.lock().unwrap() = Some(cx.waker().clone());
Poll::Pending::<()>
})
.await;
});
future::block_on(ex.tick());
assert!(WAKER.lock().unwrap().is_some());
assert_eq!(DROP.load(Ordering::SeqCst), 0);
drop(ex);
assert_eq!(DROP.load(Ordering::SeqCst), 1);
assert!(catch_unwind(|| future::block_on(task)).is_err());
assert_eq!(DROP.load(Ordering::SeqCst), 1);
}
struct CallOnDrop<F: Fn()>(F);
impl<F: Fn()> Drop for CallOnDrop<F> {
fn drop(&mut self) {
(self.0)();
}
}