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//! Async executors.
//!
//! This crate provides two reference executors that trade performance for
//! functionality. They should be considered reference executors that are "good
//! enough" for most use cases. For more specialized use cases, consider writing
//! your own executor on top of [`async-task`].
//!
//! [`async-task`]: https://crates.io/crates/async-task
//!
//! # Examples
//!
//! ```
//! use async_executor::Executor;
//! use futures_lite::future;
//!
//! // Create a new executor.
//! let ex = Executor::new();
//!
//! // Spawn a task.
//! let task = ex.spawn(async {
//! println!("Hello world");
//! });
//!
//! // Run the executor until the task completes.
//! future::block_on(ex.run(task));
//! ```
#![warn(
missing_docs,
missing_debug_implementations,
rust_2018_idioms,
clippy::undocumented_unsafe_blocks
)]
#![doc(
html_favicon_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
)]
#![doc(
html_logo_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
)]
#![cfg_attr(docsrs, feature(doc_cfg, doc_auto_cfg))]
use std::fmt;
use std::marker::PhantomData;
use std::panic::{RefUnwindSafe, UnwindSafe};
use std::rc::Rc;
use std::sync::atomic::{AtomicBool, AtomicPtr, Ordering};
use std::sync::{Arc, Mutex, RwLock, TryLockError};
use std::task::{Poll, Waker};
use async_task::{Builder, Runnable};
use concurrent_queue::ConcurrentQueue;
use futures_lite::{future, prelude::*};
use slab::Slab;
#[cfg(feature = "static")]
mod static_executors;
#[doc(no_inline)]
pub use async_task::{FallibleTask, Task};
#[cfg(feature = "static")]
#[cfg_attr(docsrs, doc(cfg(any(feature = "static"))))]
pub use static_executors::*;
/// An async executor.
///
/// # Examples
///
/// A multi-threaded executor:
///
/// ```
/// use async_channel::unbounded;
/// use async_executor::Executor;
/// use easy_parallel::Parallel;
/// use futures_lite::future;
///
/// let ex = Executor::new();
/// let (signal, shutdown) = unbounded::<()>();
///
/// Parallel::new()
/// // Run four executor threads.
/// .each(0..4, |_| future::block_on(ex.run(shutdown.recv())))
/// // Run the main future on the current thread.
/// .finish(|| future::block_on(async {
/// println!("Hello world!");
/// drop(signal);
/// }));
/// ```
pub struct Executor<'a> {
/// The executor state.
state: AtomicPtr<State>,
/// Makes the `'a` lifetime invariant.
_marker: PhantomData<std::cell::UnsafeCell<&'a ()>>,
}
// SAFETY: Executor stores no thread local state that can be accessed via other thread.
unsafe impl Send for Executor<'_> {}
// SAFETY: Executor internally synchronizes all of it's operations internally.
unsafe impl Sync for Executor<'_> {}
impl UnwindSafe for Executor<'_> {}
impl RefUnwindSafe for Executor<'_> {}
impl fmt::Debug for Executor<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
debug_executor(self, "Executor", f)
}
}
impl<'a> Executor<'a> {
/// Creates a new executor.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
///
/// let ex = Executor::new();
/// ```
pub const fn new() -> Executor<'a> {
Executor {
state: AtomicPtr::new(std::ptr::null_mut()),
_marker: PhantomData,
}
}
/// Returns `true` if there are no unfinished tasks.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
///
/// let ex = Executor::new();
/// assert!(ex.is_empty());
///
/// let task = ex.spawn(async {
/// println!("Hello world");
/// });
/// assert!(!ex.is_empty());
///
/// assert!(ex.try_tick());
/// assert!(ex.is_empty());
/// ```
pub fn is_empty(&self) -> bool {
self.state().active.lock().unwrap().is_empty()
}
/// Spawns a task onto the executor.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
///
/// let ex = Executor::new();
///
/// let task = ex.spawn(async {
/// println!("Hello world");
/// });
/// ```
pub fn spawn<T: Send + 'a>(&self, future: impl Future<Output = T> + Send + 'a) -> Task<T> {
let mut active = self.state().active.lock().unwrap();
// SAFETY: `T` and the future are `Send`.
unsafe { self.spawn_inner(future, &mut active) }
}
/// Spawns many tasks onto the executor.
///
/// As opposed to the [`spawn`] method, this locks the executor's inner task lock once and
/// spawns all of the tasks in one go. With large amounts of tasks this can improve
/// contention.
///
/// For very large numbers of tasks the lock is occasionally dropped and re-acquired to
/// prevent runner thread starvation. It is assumed that the iterator provided does not
/// block; blocking iterators can lock up the internal mutex and therefore the entire
/// executor.
///
/// ## Example
///
/// ```
/// use async_executor::Executor;
/// use futures_lite::{stream, prelude::*};
/// use std::future::ready;
///
/// # futures_lite::future::block_on(async {
/// let mut ex = Executor::new();
///
/// let futures = [
/// ready(1),
/// ready(2),
/// ready(3)
/// ];
///
/// // Spawn all of the futures onto the executor at once.
/// let mut tasks = vec![];
/// ex.spawn_many(futures, &mut tasks);
///
/// // Await all of them.
/// let results = ex.run(async move {
/// stream::iter(tasks).then(|x| x).collect::<Vec<_>>().await
/// }).await;
/// assert_eq!(results, [1, 2, 3]);
/// # });
/// ```
///
/// [`spawn`]: Executor::spawn
pub fn spawn_many<T: Send + 'a, F: Future<Output = T> + Send + 'a>(
&self,
futures: impl IntoIterator<Item = F>,
handles: &mut impl Extend<Task<F::Output>>,
) {
let mut active = Some(self.state().active.lock().unwrap());
// Convert the futures into tasks.
let tasks = futures.into_iter().enumerate().map(move |(i, future)| {
// SAFETY: `T` and the future are `Send`.
let task = unsafe { self.spawn_inner(future, active.as_mut().unwrap()) };
// Yield the lock every once in a while to ease contention.
if i.wrapping_sub(1) % 500 == 0 {
drop(active.take());
active = Some(self.state().active.lock().unwrap());
}
task
});
// Push the tasks to the user's collection.
handles.extend(tasks);
}
/// Spawn a future while holding the inner lock.
///
/// # Safety
///
/// If this is an `Executor`, `F` and `T` must be `Send`.
unsafe fn spawn_inner<T: 'a>(
&self,
future: impl Future<Output = T> + 'a,
active: &mut Slab<Waker>,
) -> Task<T> {
// Remove the task from the set of active tasks when the future finishes.
let entry = active.vacant_entry();
let index = entry.key();
let state = self.state_as_arc();
let future = async move {
let _guard = CallOnDrop(move || drop(state.active.lock().unwrap().try_remove(index)));
future.await
};
// Create the task and register it in the set of active tasks.
//
// SAFETY:
//
// If `future` is not `Send`, this must be a `LocalExecutor` as per this
// function's unsafe precondition. Since `LocalExecutor` is `!Sync`,
// `try_tick`, `tick` and `run` can only be called from the origin
// thread of the `LocalExecutor`. Similarly, `spawn` can only be called
// from the origin thread, ensuring that `future` and the executor share
// the same origin thread. The `Runnable` can be scheduled from other
// threads, but because of the above `Runnable` can only be called or
// dropped on the origin thread.
//
// `future` is not `'static`, but we make sure that the `Runnable` does
// not outlive `'a`. When the executor is dropped, the `active` field is
// drained and all of the `Waker`s are woken. Then, the queue inside of
// the `Executor` is drained of all of its runnables. This ensures that
// runnables are dropped and this precondition is satisfied.
//
// `self.schedule()` is `Send`, `Sync` and `'static`, as checked below.
// Therefore we do not need to worry about what is done with the
// `Waker`.
let (runnable, task) = Builder::new()
.propagate_panic(true)
.spawn_unchecked(|()| future, self.schedule());
entry.insert(runnable.waker());
runnable.schedule();
task
}
/// Attempts to run a task if at least one is scheduled.
///
/// Running a scheduled task means simply polling its future once.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
///
/// let ex = Executor::new();
/// assert!(!ex.try_tick()); // no tasks to run
///
/// let task = ex.spawn(async {
/// println!("Hello world");
/// });
/// assert!(ex.try_tick()); // a task was found
/// ```
pub fn try_tick(&self) -> bool {
self.state().try_tick()
}
/// Runs a single task.
///
/// Running a task means simply polling its future once.
///
/// If no tasks are scheduled when this method is called, it will wait until one is scheduled.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
/// use futures_lite::future;
///
/// let ex = Executor::new();
///
/// let task = ex.spawn(async {
/// println!("Hello world");
/// });
/// future::block_on(ex.tick()); // runs the task
/// ```
pub async fn tick(&self) {
self.state().tick().await;
}
/// Runs the executor until the given future completes.
///
/// # Examples
///
/// ```
/// use async_executor::Executor;
/// use futures_lite::future;
///
/// let ex = Executor::new();
///
/// let task = ex.spawn(async { 1 + 2 });
/// let res = future::block_on(ex.run(async { task.await * 2 }));
///
/// assert_eq!(res, 6);
/// ```
pub async fn run<T>(&self, future: impl Future<Output = T>) -> T {
self.state().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.state_as_arc();
// TODO: If possible, push into the current local queue and notify the ticker.
move |runnable| {
state.queue.push(runnable).unwrap();
state.notify();
}
}
/// Returns a pointer to the inner state.
#[inline]
fn state_ptr(&self) -> *const State {
#[cold]
fn alloc_state(atomic_ptr: &AtomicPtr<State>) -> *mut State {
let state = Arc::new(State::new());
// TODO: Switch this to use cast_mut once the MSRV can be bumped past 1.65
let ptr = Arc::into_raw(state) as *mut State;
if let Err(actual) = atomic_ptr.compare_exchange(
std::ptr::null_mut(),
ptr,
Ordering::AcqRel,
Ordering::Acquire,
) {
// SAFETY: This was just created from Arc::into_raw.
drop(unsafe { Arc::from_raw(ptr) });
actual
} else {
ptr
}
}
let mut ptr = self.state.load(Ordering::Acquire);
if ptr.is_null() {
ptr = alloc_state(&self.state);
}
ptr
}
/// Returns a reference to the inner state.
#[inline]
fn state(&self) -> &State {
// SAFETY: So long as an Executor lives, it's state pointer will always be valid
// when accessed through state_ptr.
unsafe { &*self.state_ptr() }
}
// Clones the inner state Arc
#[inline]
fn state_as_arc(&self) -> Arc<State> {
// SAFETY: So long as an Executor lives, it's state pointer will always be a valid
// Arc when accessed through state_ptr.
let arc = unsafe { Arc::from_raw(self.state_ptr()) };
let clone = arc.clone();
std::mem::forget(arc);
clone
}
}
impl Drop for Executor<'_> {
fn drop(&mut self) {
let ptr = *self.state.get_mut();
if ptr.is_null() {
return;
}
// SAFETY: As ptr is not null, it was allocated via Arc::new and converted
// via Arc::into_raw in state_ptr.
let state = unsafe { Arc::from_raw(ptr) };
let mut active = state.active.lock().unwrap_or_else(|e| e.into_inner());
for w in active.drain() {
w.wake();
}
drop(active);
while state.queue.pop().is_ok() {}
}
}
impl<'a> Default for Executor<'a> {
fn default() -> Executor<'a> {
Executor::new()
}
}
/// A thread-local executor.
///
/// The executor can only be run on the thread that created it.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
/// use futures_lite::future;
///
/// let local_ex = LocalExecutor::new();
///
/// future::block_on(local_ex.run(async {
/// println!("Hello world!");
/// }));
/// ```
pub struct LocalExecutor<'a> {
/// The inner executor.
inner: Executor<'a>,
/// Makes the type `!Send` and `!Sync`.
_marker: PhantomData<Rc<()>>,
}
impl UnwindSafe for LocalExecutor<'_> {}
impl RefUnwindSafe for LocalExecutor<'_> {}
impl fmt::Debug for LocalExecutor<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
debug_executor(&self.inner, "LocalExecutor", f)
}
}
impl<'a> LocalExecutor<'a> {
/// Creates a single-threaded executor.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
///
/// let local_ex = LocalExecutor::new();
/// ```
pub const fn new() -> LocalExecutor<'a> {
LocalExecutor {
inner: Executor::new(),
_marker: PhantomData,
}
}
/// Returns `true` if there are no unfinished tasks.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
///
/// let local_ex = LocalExecutor::new();
/// assert!(local_ex.is_empty());
///
/// let task = local_ex.spawn(async {
/// println!("Hello world");
/// });
/// assert!(!local_ex.is_empty());
///
/// assert!(local_ex.try_tick());
/// assert!(local_ex.is_empty());
/// ```
pub fn is_empty(&self) -> bool {
self.inner().is_empty()
}
/// Spawns a task onto the executor.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
///
/// let local_ex = LocalExecutor::new();
///
/// let task = local_ex.spawn(async {
/// println!("Hello world");
/// });
/// ```
pub fn spawn<T: 'a>(&self, future: impl Future<Output = T> + 'a) -> Task<T> {
let mut active = self.inner().state().active.lock().unwrap();
// SAFETY: This executor is not thread safe, so the future and its result
// cannot be sent to another thread.
unsafe { self.inner().spawn_inner(future, &mut active) }
}
/// Spawns many tasks onto the executor.
///
/// As opposed to the [`spawn`] method, this locks the executor's inner task lock once and
/// spawns all of the tasks in one go. With large amounts of tasks this can improve
/// contention.
///
/// It is assumed that the iterator provided does not block; blocking iterators can lock up
/// the internal mutex and therefore the entire executor. Unlike [`Executor::spawn`], the
/// mutex is not released, as there are no other threads that can poll this executor.
///
/// ## Example
///
/// ```
/// use async_executor::LocalExecutor;
/// use futures_lite::{stream, prelude::*};
/// use std::future::ready;
///
/// # futures_lite::future::block_on(async {
/// let mut ex = LocalExecutor::new();
///
/// let futures = [
/// ready(1),
/// ready(2),
/// ready(3)
/// ];
///
/// // Spawn all of the futures onto the executor at once.
/// let mut tasks = vec![];
/// ex.spawn_many(futures, &mut tasks);
///
/// // Await all of them.
/// let results = ex.run(async move {
/// stream::iter(tasks).then(|x| x).collect::<Vec<_>>().await
/// }).await;
/// assert_eq!(results, [1, 2, 3]);
/// # });
/// ```
///
/// [`spawn`]: LocalExecutor::spawn
/// [`Executor::spawn_many`]: Executor::spawn_many
pub fn spawn_many<T: 'a, F: Future<Output = T> + 'a>(
&self,
futures: impl IntoIterator<Item = F>,
handles: &mut impl Extend<Task<F::Output>>,
) {
let mut active = self.inner().state().active.lock().unwrap();
// Convert all of the futures to tasks.
let tasks = futures.into_iter().map(|future| {
// SAFETY: This executor is not thread safe, so the future and its result
// cannot be sent to another thread.
unsafe { self.inner().spawn_inner(future, &mut active) }
// As only one thread can spawn or poll tasks at a time, there is no need
// to release lock contention here.
});
// Push them to the user's collection.
handles.extend(tasks);
}
/// Attempts to run a task if at least one is scheduled.
///
/// Running a scheduled task means simply polling its future once.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
///
/// let ex = LocalExecutor::new();
/// assert!(!ex.try_tick()); // no tasks to run
///
/// let task = ex.spawn(async {
/// println!("Hello world");
/// });
/// assert!(ex.try_tick()); // a task was found
/// ```
pub fn try_tick(&self) -> bool {
self.inner().try_tick()
}
/// Runs a single task.
///
/// Running a task means simply polling its future once.
///
/// If no tasks are scheduled when this method is called, it will wait until one is scheduled.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
/// use futures_lite::future;
///
/// let ex = LocalExecutor::new();
///
/// let task = ex.spawn(async {
/// println!("Hello world");
/// });
/// future::block_on(ex.tick()); // runs the task
/// ```
pub async fn tick(&self) {
self.inner().tick().await
}
/// Runs the executor until the given future completes.
///
/// # Examples
///
/// ```
/// use async_executor::LocalExecutor;
/// use futures_lite::future;
///
/// let local_ex = LocalExecutor::new();
///
/// let task = local_ex.spawn(async { 1 + 2 });
/// let res = future::block_on(local_ex.run(async { task.await * 2 }));
///
/// assert_eq!(res, 6);
/// ```
pub async fn run<T>(&self, future: impl Future<Output = T>) -> T {
self.inner().run(future).await
}
/// Returns a reference to the inner executor.
fn inner(&self) -> &Executor<'a> {
&self.inner
}
}
impl<'a> Default for LocalExecutor<'a> {
fn default() -> LocalExecutor<'a> {
LocalExecutor::new()
}
}
/// The state of a executor.
struct State {
/// The global queue.
queue: ConcurrentQueue<Runnable>,
/// Local queues created by runners.
local_queues: RwLock<Vec<Arc<ConcurrentQueue<Runnable>>>>,
/// Set to `true` when a sleeping ticker is notified or no tickers are sleeping.
notified: AtomicBool,
/// A list of sleeping tickers.
sleepers: Mutex<Sleepers>,
/// Currently active tasks.
active: Mutex<Slab<Waker>>,
}
impl State {
/// Creates state for a new executor.
const fn new() -> State {
State {
queue: ConcurrentQueue::unbounded(),
local_queues: RwLock::new(Vec::new()),
notified: AtomicBool::new(true),
sleepers: Mutex::new(Sleepers {
count: 0,
wakers: Vec::new(),
free_ids: Vec::new(),
}),
active: Mutex::new(Slab::new()),
}
}
/// Notifies a sleeping ticker.
#[inline]
fn notify(&self) {
if self
.notified
.compare_exchange(false, true, Ordering::AcqRel, Ordering::Acquire)
.is_ok()
{
let waker = self.sleepers.lock().unwrap().notify();
if let Some(w) = waker {
w.wake();
}
}
}
pub(crate) fn try_tick(&self) -> bool {
match self.queue.pop() {
Err(_) => false,
Ok(runnable) => {
// Notify another ticker now to pick up where this ticker left off, just in case
// running the task takes a long time.
self.notify();
// Run the task.
runnable.run();
true
}
}
}
pub(crate) async fn tick(&self) {
let runnable = Ticker::new(self).runnable().await;
runnable.run();
}
pub async fn run<T>(&self, future: impl Future<Output = T>) -> T {
let mut runner = Runner::new(self);
let mut rng = fastrand::Rng::new();
// A future that runs tasks forever.
let run_forever = async {
loop {
for _ in 0..200 {
let runnable = runner.runnable(&mut rng).await;
runnable.run();
}
future::yield_now().await;
}
};
// Run `future` and `run_forever` concurrently until `future` completes.
future.or(run_forever).await
}
}
/// A list of sleeping tickers.
struct Sleepers {
/// Number of sleeping tickers (both notified and unnotified).
count: usize,
/// IDs and wakers of sleeping unnotified tickers.
///
/// A sleeping ticker is notified when its waker is missing from this list.
wakers: Vec<(usize, Waker)>,
/// Reclaimed IDs.
free_ids: Vec<usize>,
}
impl Sleepers {
/// Inserts a new sleeping ticker.
fn insert(&mut self, waker: &Waker) -> usize {
let id = match self.free_ids.pop() {
Some(id) => id,
None => self.count + 1,
};
self.count += 1;
self.wakers.push((id, waker.clone()));
id
}
/// Re-inserts a sleeping ticker's waker if it was notified.
///
/// Returns `true` if the ticker was notified.
fn update(&mut self, id: usize, waker: &Waker) -> bool {
for item in &mut self.wakers {
if item.0 == id {
item.1.clone_from(waker);
return false;
}
}
self.wakers.push((id, waker.clone()));
true
}
/// Removes a previously inserted sleeping ticker.
///
/// Returns `true` if the ticker was notified.
fn remove(&mut self, id: usize) -> bool {
self.count -= 1;
self.free_ids.push(id);
for i in (0..self.wakers.len()).rev() {
if self.wakers[i].0 == id {
self.wakers.remove(i);
return false;
}
}
true
}
/// Returns `true` if a sleeping ticker is notified or no tickers are sleeping.
fn is_notified(&self) -> bool {
self.count == 0 || self.count > self.wakers.len()
}
/// Returns notification waker for a sleeping ticker.
///
/// If a ticker was notified already or there are no tickers, `None` will be returned.
fn notify(&mut self) -> Option<Waker> {
if self.wakers.len() == self.count {
self.wakers.pop().map(|item| item.1)
} else {
None
}
}
}
/// Runs task one by one.
struct Ticker<'a> {
/// The executor state.
state: &'a State,
/// Set to a non-zero sleeper ID when in sleeping state.
///
/// States a ticker can be in:
/// 1) Woken.
/// 2a) Sleeping and unnotified.
/// 2b) Sleeping and notified.
sleeping: usize,
}
impl Ticker<'_> {
/// Creates a ticker.
fn new(state: &State) -> Ticker<'_> {
Ticker { state, sleeping: 0 }
}
/// Moves the ticker into sleeping and unnotified state.
///
/// Returns `false` if the ticker was already sleeping and unnotified.
fn sleep(&mut self, waker: &Waker) -> bool {
let mut sleepers = self.state.sleepers.lock().unwrap();
match self.sleeping {
// Move to sleeping state.
0 => {
self.sleeping = sleepers.insert(waker);
}
// Already sleeping, check if notified.
id => {
if !sleepers.update(id, waker) {
return false;
}
}
}
self.state
.notified
.store(sleepers.is_notified(), Ordering::Release);
true
}
/// Moves the ticker into woken state.
fn wake(&mut self) {
if self.sleeping != 0 {
let mut sleepers = self.state.sleepers.lock().unwrap();
sleepers.remove(self.sleeping);
self.state
.notified
.store(sleepers.is_notified(), Ordering::Release);
}
self.sleeping = 0;
}
/// Waits for the next runnable task to run.
async fn runnable(&mut self) -> Runnable {
self.runnable_with(|| self.state.queue.pop().ok()).await
}
/// Waits for the next runnable task to run, given a function that searches for a task.
async fn runnable_with(&mut self, mut search: impl FnMut() -> Option<Runnable>) -> Runnable {
future::poll_fn(|cx| {
loop {
match search() {
None => {
// Move to sleeping and unnotified state.
if !self.sleep(cx.waker()) {
// If already sleeping and unnotified, return.
return Poll::Pending;
}
}
Some(r) => {
// Wake up.
self.wake();
// Notify another ticker now to pick up where this ticker left off, just in
// case running the task takes a long time.
self.state.notify();
return Poll::Ready(r);
}
}
}
})
.await
}
}
impl Drop for Ticker<'_> {
fn drop(&mut self) {
// If this ticker is in sleeping state, it must be removed from the sleepers list.
if self.sleeping != 0 {
let mut sleepers = self.state.sleepers.lock().unwrap();
let notified = sleepers.remove(self.sleeping);
self.state
.notified
.store(sleepers.is_notified(), Ordering::Release);
// If this ticker was notified, then notify another ticker.
if notified {
drop(sleepers);
self.state.notify();
}
}
}
}
/// A worker in a work-stealing executor.
///
/// This is just a ticker that also has an associated local queue for improved cache locality.
struct Runner<'a> {
/// The executor state.
state: &'a State,
/// Inner ticker.
ticker: Ticker<'a>,
/// The local queue.
local: Arc<ConcurrentQueue<Runnable>>,
/// Bumped every time a runnable task is found.
ticks: usize,
}
impl Runner<'_> {
/// Creates a runner and registers it in the executor state.
fn new(state: &State) -> Runner<'_> {
let runner = Runner {
state,
ticker: Ticker::new(state),
local: Arc::new(ConcurrentQueue::bounded(512)),
ticks: 0,
};
state
.local_queues
.write()
.unwrap()
.push(runner.local.clone());
runner
}
/// Waits for the next runnable task to run.
async fn runnable(&mut self, rng: &mut fastrand::Rng) -> Runnable {
let runnable = self
.ticker
.runnable_with(|| {
// Try the local queue.
if let Ok(r) = self.local.pop() {
return Some(r);
}
// Try stealing from the global queue.
if let Ok(r) = self.state.queue.pop() {
steal(&self.state.queue, &self.local);
return Some(r);
}
// Try stealing from other runners.
let local_queues = self.state.local_queues.read().unwrap();
// Pick a random starting point in the iterator list and rotate the list.
let n = local_queues.len();
let start = rng.usize(..n);
let iter = local_queues
.iter()
.chain(local_queues.iter())
.skip(start)
.take(n);
// Remove this runner's local queue.
let iter = iter.filter(|local| !Arc::ptr_eq(local, &self.local));
// Try stealing from each local queue in the list.
for local in iter {
steal(local, &self.local);
if let Ok(r) = self.local.pop() {
return Some(r);
}
}
None
})
.await;
// Bump the tick counter.
self.ticks = self.ticks.wrapping_add(1);
if self.ticks % 64 == 0 {
// Steal tasks from the global queue to ensure fair task scheduling.
steal(&self.state.queue, &self.local);
}
runnable
}
}
impl Drop for Runner<'_> {
fn drop(&mut self) {
// Remove the local queue.
self.state
.local_queues
.write()
.unwrap()
.retain(|local| !Arc::ptr_eq(local, &self.local));
// Re-schedule remaining tasks in the local queue.
while let Ok(r) = self.local.pop() {
r.schedule();
}
}
}
/// Steals some items from one queue into another.
fn steal<T>(src: &ConcurrentQueue<T>, dest: &ConcurrentQueue<T>) {
// Half of `src`'s length rounded up.
let mut count = (src.len() + 1) / 2;
if count > 0 {
// Don't steal more than fits into the queue.
if let Some(cap) = dest.capacity() {
count = count.min(cap - dest.len());
}
// Steal tasks.
for _ in 0..count {
if let Ok(t) = src.pop() {
assert!(dest.push(t).is_ok());
} else {
break;
}
}
}
}
/// Debug implementation for `Executor` and `LocalExecutor`.
fn debug_executor(executor: &Executor<'_>, name: &str, f: &mut fmt::Formatter<'_>) -> fmt::Result {
// Get a reference to the state.
let ptr = executor.state.load(Ordering::Acquire);
if ptr.is_null() {
// The executor has not been initialized.
struct Uninitialized;
impl fmt::Debug for Uninitialized {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("<uninitialized>")
}
}
return f.debug_tuple(name).field(&Uninitialized).finish();
}
// SAFETY: If the state pointer is not null, it must have been
// allocated properly by Arc::new and converted via Arc::into_raw
// in state_ptr.
let state = unsafe { &*ptr };
debug_state(state, name, f)
}
/// Debug implementation for `Executor` and `LocalExecutor`.
fn debug_state(state: &State, name: &str, f: &mut fmt::Formatter<'_>) -> fmt::Result {
/// Debug wrapper for the number of active tasks.
struct ActiveTasks<'a>(&'a Mutex<Slab<Waker>>);
impl fmt::Debug for ActiveTasks<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.0.try_lock() {
Ok(lock) => fmt::Debug::fmt(&lock.len(), f),
Err(TryLockError::WouldBlock) => f.write_str("<locked>"),
Err(TryLockError::Poisoned(_)) => f.write_str("<poisoned>"),
}
}
}
/// Debug wrapper for the local runners.
struct LocalRunners<'a>(&'a RwLock<Vec<Arc<ConcurrentQueue<Runnable>>>>);
impl fmt::Debug for LocalRunners<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.0.try_read() {
Ok(lock) => f
.debug_list()
.entries(lock.iter().map(|queue| queue.len()))
.finish(),
Err(TryLockError::WouldBlock) => f.write_str("<locked>"),
Err(TryLockError::Poisoned(_)) => f.write_str("<poisoned>"),
}
}
}
/// Debug wrapper for the sleepers.
struct SleepCount<'a>(&'a Mutex<Sleepers>);
impl fmt::Debug for SleepCount<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.0.try_lock() {
Ok(lock) => fmt::Debug::fmt(&lock.count, f),
Err(TryLockError::WouldBlock) => f.write_str("<locked>"),
Err(TryLockError::Poisoned(_)) => f.write_str("<poisoned>"),
}
}
}
f.debug_struct(name)
.field("active", &ActiveTasks(&state.active))
.field("global_tasks", &state.queue.len())
.field("local_runners", &LocalRunners(&state.local_queues))
.field("sleepers", &SleepCount(&state.sleepers))
.finish()
}
/// Runs a closure when dropped.
struct CallOnDrop<F: FnMut()>(F);
impl<F: FnMut()> Drop for CallOnDrop<F> {
fn drop(&mut self) {
(self.0)();
}
}
fn _ensure_send_and_sync() {
use futures_lite::future::pending;
fn is_send<T: Send>(_: T) {}
fn is_sync<T: Sync>(_: T) {}
fn is_static<T: 'static>(_: T) {}
is_send::<Executor<'_>>(Executor::new());
is_sync::<Executor<'_>>(Executor::new());
let ex = Executor::new();
is_send(ex.run(pending::<()>()));
is_sync(ex.run(pending::<()>()));
is_send(ex.tick());
is_sync(ex.tick());
is_send(ex.schedule());
is_sync(ex.schedule());
is_static(ex.schedule());
/// ```compile_fail
/// use async_executor::LocalExecutor;
/// use futures_lite::future::pending;
///
/// fn is_send<T: Send>(_: T) {}
/// fn is_sync<T: Sync>(_: T) {}
///
/// is_send::<LocalExecutor<'_>>(LocalExecutor::new());
/// is_sync::<LocalExecutor<'_>>(LocalExecutor::new());
///
/// let ex = LocalExecutor::new();
/// is_send(ex.run(pending::<()>()));
/// is_sync(ex.run(pending::<()>()));
/// is_send(ex.tick());
/// is_sync(ex.tick());
/// ```
fn _negative_test() {}
}