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use core::fmt;
use core::future::Future;
use core::marker::PhantomData;
use core::mem;
use core::ptr::NonNull;
use core::sync::atomic::Ordering;
use core::task::Waker;
use alloc::boxed::Box;
use crate::header::Header;
use crate::raw::RawTask;
use crate::state::*;
use crate::Task;
mod sealed {
use super::*;
pub trait Sealed<M> {}
impl<M, F> Sealed<M> for F where F: Fn(Runnable<M>) {}
impl<M, F> Sealed<M> for WithInfo<F> where F: Fn(Runnable<M>, ScheduleInfo) {}
}
/// A builder that creates a new task.
#[derive(Debug)]
pub struct Builder<M> {
/// The metadata associated with the task.
pub(crate) metadata: M,
/// Whether or not a panic that occurs in the task should be propagated.
#[cfg(feature = "std")]
pub(crate) propagate_panic: bool,
}
impl<M: Default> Default for Builder<M> {
fn default() -> Self {
Builder::new().metadata(M::default())
}
}
/// Extra scheduling information that can be passed to the scheduling function.
///
/// The data source of this struct is directly from the actual implementation
/// of the crate itself, different from [`Runnable`]'s metadata, which is
/// managed by the caller.
///
/// # Examples
///
/// ```
/// use async_task::{Runnable, ScheduleInfo, WithInfo};
/// use std::sync::{Arc, Mutex};
///
/// // The future inside the task.
/// let future = async {
/// println!("Hello, world!");
/// };
///
/// // If the task gets woken up while running, it will be sent into this channel.
/// let (s, r) = flume::unbounded();
/// // Otherwise, it will be placed into this slot.
/// let lifo_slot = Arc::new(Mutex::new(None));
/// let schedule = move |runnable: Runnable, info: ScheduleInfo| {
/// if info.woken_while_running {
/// s.send(runnable).unwrap()
/// } else {
/// let last = lifo_slot.lock().unwrap().replace(runnable);
/// if let Some(last) = last {
/// s.send(last).unwrap()
/// }
/// }
/// };
///
/// // Create the actual scheduler to be spawned with some future.
/// let scheduler = WithInfo(schedule);
/// // Create a task with the future and the scheduler.
/// let (runnable, task) = async_task::spawn(future, scheduler);
/// ```
#[derive(Debug, Copy, Clone)]
#[non_exhaustive]
pub struct ScheduleInfo {
/// Indicates whether the task gets woken up while running.
///
/// It is set to true usually because the task has yielded itself to the
/// scheduler.
pub woken_while_running: bool,
}
impl ScheduleInfo {
pub(crate) fn new(woken_while_running: bool) -> Self {
ScheduleInfo {
woken_while_running,
}
}
}
/// The trait for scheduling functions.
pub trait Schedule<M = ()>: sealed::Sealed<M> {
/// The actual scheduling procedure.
fn schedule(&self, runnable: Runnable<M>, info: ScheduleInfo);
}
impl<M, F> Schedule<M> for F
where
F: Fn(Runnable<M>),
{
fn schedule(&self, runnable: Runnable<M>, _: ScheduleInfo) {
self(runnable)
}
}
/// Pass a scheduling function with more scheduling information - a.k.a.
/// [`ScheduleInfo`].
///
/// Sometimes, it's useful to pass the runnable's state directly to the
/// scheduling function, such as whether it's woken up while running. The
/// scheduler can thus use the information to determine its scheduling
/// strategy.
///
/// The data source of [`ScheduleInfo`] is directly from the actual
/// implementation of the crate itself, different from [`Runnable`]'s metadata,
/// which is managed by the caller.
///
/// # Examples
///
/// ```
/// use async_task::{ScheduleInfo, WithInfo};
/// use std::sync::{Arc, Mutex};
///
/// // The future inside the task.
/// let future = async {
/// println!("Hello, world!");
/// };
///
/// // If the task gets woken up while running, it will be sent into this channel.
/// let (s, r) = flume::unbounded();
/// // Otherwise, it will be placed into this slot.
/// let lifo_slot = Arc::new(Mutex::new(None));
/// let schedule = move |runnable, info: ScheduleInfo| {
/// if info.woken_while_running {
/// s.send(runnable).unwrap()
/// } else {
/// let last = lifo_slot.lock().unwrap().replace(runnable);
/// if let Some(last) = last {
/// s.send(last).unwrap()
/// }
/// }
/// };
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = async_task::spawn(future, WithInfo(schedule));
/// ```
#[derive(Debug)]
pub struct WithInfo<F>(pub F);
impl<F> From<F> for WithInfo<F> {
fn from(value: F) -> Self {
WithInfo(value)
}
}
impl<M, F> Schedule<M> for WithInfo<F>
where
F: Fn(Runnable<M>, ScheduleInfo),
{
fn schedule(&self, runnable: Runnable<M>, info: ScheduleInfo) {
(self.0)(runnable, info)
}
}
impl Builder<()> {
/// Creates a new task builder.
///
/// By default, this task builder has no metadata. Use the [`metadata`] method to
/// set the metadata.
///
/// # Examples
///
/// ```
/// use async_task::Builder;
///
/// let (runnable, task) = Builder::new().spawn(|()| async {}, |_| {});
/// ```
pub fn new() -> Builder<()> {
Builder {
metadata: (),
#[cfg(feature = "std")]
propagate_panic: false,
}
}
/// Adds metadata to the task.
///
/// In certain cases, it may be useful to associate some metadata with a task. For instance,
/// you may want to associate a name with a task, or a priority for a priority queue. This
/// method allows the user to attach arbitrary metadata to a task that is available through
/// the [`Runnable`] or the [`Task`].
///
/// # Examples
///
/// This example creates an executor that associates a "priority" number with each task, and
/// then runs the tasks in order of priority.
///
/// ```
/// use async_task::{Builder, Runnable};
/// use once_cell::sync::Lazy;
/// use std::cmp;
/// use std::collections::BinaryHeap;
/// use std::sync::Mutex;
///
/// # smol::future::block_on(async {
/// /// A wrapper around a `Runnable<usize>` that implements `Ord` so that it can be used in a
/// /// priority queue.
/// struct TaskWrapper(Runnable<usize>);
///
/// impl PartialEq for TaskWrapper {
/// fn eq(&self, other: &Self) -> bool {
/// self.0.metadata() == other.0.metadata()
/// }
/// }
///
/// impl Eq for TaskWrapper {}
///
/// impl PartialOrd for TaskWrapper {
/// fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
/// Some(self.cmp(other))
/// }
/// }
///
/// impl Ord for TaskWrapper {
/// fn cmp(&self, other: &Self) -> cmp::Ordering {
/// self.0.metadata().cmp(other.0.metadata())
/// }
/// }
///
/// static EXECUTOR: Lazy<Mutex<BinaryHeap<TaskWrapper>>> = Lazy::new(|| {
/// Mutex::new(BinaryHeap::new())
/// });
///
/// let schedule = |runnable| {
/// EXECUTOR.lock().unwrap().push(TaskWrapper(runnable));
/// };
///
/// // Spawn a few tasks with different priorities.
/// let spawn_task = move |priority| {
/// let (runnable, task) = Builder::new().metadata(priority).spawn(
/// move |_| async move { priority },
/// schedule,
/// );
/// runnable.schedule();
/// task
/// };
///
/// let t1 = spawn_task(1);
/// let t2 = spawn_task(2);
/// let t3 = spawn_task(3);
///
/// // Run the tasks in order of priority.
/// let mut metadata_seen = vec![];
/// while let Some(TaskWrapper(runnable)) = EXECUTOR.lock().unwrap().pop() {
/// metadata_seen.push(*runnable.metadata());
/// runnable.run();
/// }
///
/// assert_eq!(metadata_seen, vec![3, 2, 1]);
/// assert_eq!(t1.await, 1);
/// assert_eq!(t2.await, 2);
/// assert_eq!(t3.await, 3);
/// # });
/// ```
pub fn metadata<M>(self, metadata: M) -> Builder<M> {
Builder {
metadata,
#[cfg(feature = "std")]
propagate_panic: self.propagate_panic,
}
}
}
impl<M> Builder<M> {
/// Propagates panics that occur in the task.
///
/// When this is `true`, panics that occur in the task will be propagated to the caller of
/// the [`Task`]. When this is false, no special action is taken when a panic occurs in the
/// task, meaning that the caller of [`Runnable::run`] will observe a panic.
///
/// This is only available when the `std` feature is enabled. By default, this is `false`.
///
/// # Examples
///
/// ```
/// use async_task::Builder;
/// use futures_lite::future::poll_fn;
/// use std::future::Future;
/// use std::panic;
/// use std::pin::Pin;
/// use std::task::{Context, Poll};
///
/// fn did_panic<F: FnOnce()>(f: F) -> bool {
/// panic::catch_unwind(panic::AssertUnwindSafe(f)).is_err()
/// }
///
/// # smol::future::block_on(async {
/// let (runnable1, mut task1) = Builder::new()
/// .propagate_panic(true)
/// .spawn(|()| async move { panic!() }, |_| {});
///
/// let (runnable2, mut task2) = Builder::new()
/// .propagate_panic(false)
/// .spawn(|()| async move { panic!() }, |_| {});
///
/// assert!(!did_panic(|| { runnable1.run(); }));
/// assert!(did_panic(|| { runnable2.run(); }));
///
/// let waker = poll_fn(|cx| Poll::Ready(cx.waker().clone())).await;
/// let mut cx = Context::from_waker(&waker);
/// assert!(did_panic(|| { let _ = Pin::new(&mut task1).poll(&mut cx); }));
/// assert!(did_panic(|| { let _ = Pin::new(&mut task2).poll(&mut cx); }));
/// # });
/// ```
#[cfg(feature = "std")]
pub fn propagate_panic(self, propagate_panic: bool) -> Builder<M> {
Builder {
metadata: self.metadata,
propagate_panic,
}
}
/// Creates a new task.
///
/// The returned [`Runnable`] is used to poll the `future`, and the [`Task`] is used to await its
/// output.
///
/// Method [`run()`][`Runnable::run()`] polls the task's future once. Then, the [`Runnable`]
/// vanishes and only reappears when its [`Waker`] wakes the task, thus scheduling it to be run
/// again.
///
/// When the task is woken, its [`Runnable`] is passed to the `schedule` function.
/// The `schedule` function should not attempt to run the [`Runnable`] nor to drop it. Instead, it
/// should push it into a task queue so that it can be processed later.
///
/// If you need to spawn a future that does not implement [`Send`] or isn't `'static`, consider
/// using [`spawn_local()`] or [`spawn_unchecked()`] instead.
///
/// # Examples
///
/// ```
/// use async_task::Builder;
///
/// // The future inside the task.
/// let future = async {
/// println!("Hello, world!");
/// };
///
/// // A function that schedules the task when it gets woken up.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = Builder::new().spawn(|()| future, schedule);
/// ```
pub fn spawn<F, Fut, S>(self, future: F, schedule: S) -> (Runnable<M>, Task<Fut::Output, M>)
where
F: FnOnce(&M) -> Fut,
Fut: Future + Send + 'static,
Fut::Output: Send + 'static,
S: Schedule<M> + Send + Sync + 'static,
{
unsafe { self.spawn_unchecked(future, schedule) }
}
/// Creates a new thread-local task.
///
/// This function is same as [`spawn()`], except it does not require [`Send`] on `future`. If the
/// [`Runnable`] is used or dropped on another thread, a panic will occur.
///
/// This function is only available when the `std` feature for this crate is enabled.
///
/// # Examples
///
/// ```
/// use async_task::{Builder, Runnable};
/// use flume::{Receiver, Sender};
/// use std::rc::Rc;
///
/// thread_local! {
/// // A queue that holds scheduled tasks.
/// static QUEUE: (Sender<Runnable>, Receiver<Runnable>) = flume::unbounded();
/// }
///
/// // Make a non-Send future.
/// let msg: Rc<str> = "Hello, world!".into();
/// let future = async move {
/// println!("{}", msg);
/// };
///
/// // A function that schedules the task when it gets woken up.
/// let s = QUEUE.with(|(s, _)| s.clone());
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = Builder::new().spawn_local(move |()| future, schedule);
/// ```
#[cfg(feature = "std")]
pub fn spawn_local<F, Fut, S>(
self,
future: F,
schedule: S,
) -> (Runnable<M>, Task<Fut::Output, M>)
where
F: FnOnce(&M) -> Fut,
Fut: Future + 'static,
Fut::Output: 'static,
S: Schedule<M> + Send + Sync + 'static,
{
use std::mem::ManuallyDrop;
use std::pin::Pin;
use std::task::{Context, Poll};
use std::thread::{self, ThreadId};
#[inline]
fn thread_id() -> ThreadId {
std::thread_local! {
static ID: ThreadId = thread::current().id();
}
ID.try_with(|id| *id)
.unwrap_or_else(|_| thread::current().id())
}
struct Checked<F> {
id: ThreadId,
inner: ManuallyDrop<F>,
}
impl<F> Drop for Checked<F> {
fn drop(&mut self) {
assert!(
self.id == thread_id(),
"local task dropped by a thread that didn't spawn it"
);
unsafe {
ManuallyDrop::drop(&mut self.inner);
}
}
}
impl<F: Future> Future for Checked<F> {
type Output = F::Output;
fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
assert!(
self.id == thread_id(),
"local task polled by a thread that didn't spawn it"
);
unsafe { self.map_unchecked_mut(|c| &mut *c.inner).poll(cx) }
}
}
// Wrap the future into one that checks which thread it's on.
let future = move |meta| {
let future = future(meta);
Checked {
id: thread_id(),
inner: ManuallyDrop::new(future),
}
};
unsafe { self.spawn_unchecked(future, schedule) }
}
/// Creates a new task without [`Send`], [`Sync`], and `'static` bounds.
///
/// This function is same as [`spawn()`], except it does not require [`Send`], [`Sync`], and
/// `'static` on `future` and `schedule`.
///
/// # Safety
///
/// - If `Fut` is not [`Send`], its [`Runnable`] must be used and dropped on the original
/// thread.
/// - If `Fut` is not `'static`, borrowed non-metadata variables must outlive its [`Runnable`].
/// - If `schedule` is not [`Send`] and [`Sync`], all instances of the [`Runnable`]'s [`Waker`]
/// must be used and dropped on the original thread.
/// - If `schedule` is not `'static`, borrowed variables must outlive all instances of the
/// [`Runnable`]'s [`Waker`].
///
/// # Examples
///
/// ```
/// use async_task::Builder;
///
/// // The future inside the task.
/// let future = async {
/// println!("Hello, world!");
/// };
///
/// // If the task gets woken up, it will be sent into this channel.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = unsafe { Builder::new().spawn_unchecked(move |()| future, schedule) };
/// ```
pub unsafe fn spawn_unchecked<'a, F, Fut, S>(
self,
future: F,
schedule: S,
) -> (Runnable<M>, Task<Fut::Output, M>)
where
F: FnOnce(&'a M) -> Fut,
Fut: Future + 'a,
S: Schedule<M>,
M: 'a,
{
// Allocate large futures on the heap.
let ptr = if mem::size_of::<Fut>() >= 2048 {
let future = |meta| {
let future = future(meta);
Box::pin(future)
};
RawTask::<_, Fut::Output, S, M>::allocate(future, schedule, self)
} else {
RawTask::<Fut, Fut::Output, S, M>::allocate(future, schedule, self)
};
let runnable = Runnable::from_raw(ptr);
let task = Task {
ptr,
_marker: PhantomData,
};
(runnable, task)
}
}
/// Creates a new task.
///
/// The returned [`Runnable`] is used to poll the `future`, and the [`Task`] is used to await its
/// output.
///
/// Method [`run()`][`Runnable::run()`] polls the task's future once. Then, the [`Runnable`]
/// vanishes and only reappears when its [`Waker`] wakes the task, thus scheduling it to be run
/// again.
///
/// When the task is woken, its [`Runnable`] is passed to the `schedule` function.
/// The `schedule` function should not attempt to run the [`Runnable`] nor to drop it. Instead, it
/// should push it into a task queue so that it can be processed later.
///
/// If you need to spawn a future that does not implement [`Send`] or isn't `'static`, consider
/// using [`spawn_local()`] or [`spawn_unchecked()`] instead.
///
/// # Examples
///
/// ```
/// // The future inside the task.
/// let future = async {
/// println!("Hello, world!");
/// };
///
/// // A function that schedules the task when it gets woken up.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = async_task::spawn(future, schedule);
/// ```
pub fn spawn<F, S>(future: F, schedule: S) -> (Runnable, Task<F::Output>)
where
F: Future + Send + 'static,
F::Output: Send + 'static,
S: Schedule + Send + Sync + 'static,
{
unsafe { spawn_unchecked(future, schedule) }
}
/// Creates a new thread-local task.
///
/// This function is same as [`spawn()`], except it does not require [`Send`] on `future`. If the
/// [`Runnable`] is used or dropped on another thread, a panic will occur.
///
/// This function is only available when the `std` feature for this crate is enabled.
///
/// # Examples
///
/// ```
/// use async_task::Runnable;
/// use flume::{Receiver, Sender};
/// use std::rc::Rc;
///
/// thread_local! {
/// // A queue that holds scheduled tasks.
/// static QUEUE: (Sender<Runnable>, Receiver<Runnable>) = flume::unbounded();
/// }
///
/// // Make a non-Send future.
/// let msg: Rc<str> = "Hello, world!".into();
/// let future = async move {
/// println!("{}", msg);
/// };
///
/// // A function that schedules the task when it gets woken up.
/// let s = QUEUE.with(|(s, _)| s.clone());
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = async_task::spawn_local(future, schedule);
/// ```
#[cfg(feature = "std")]
pub fn spawn_local<F, S>(future: F, schedule: S) -> (Runnable, Task<F::Output>)
where
F: Future + 'static,
F::Output: 'static,
S: Schedule + Send + Sync + 'static,
{
Builder::new().spawn_local(move |()| future, schedule)
}
/// Creates a new task without [`Send`], [`Sync`], and `'static` bounds.
///
/// This function is same as [`spawn()`], except it does not require [`Send`], [`Sync`], and
/// `'static` on `future` and `schedule`.
///
/// # Safety
///
/// - If `future` is not [`Send`], its [`Runnable`] must be used and dropped on the original
/// thread.
/// - If `future` is not `'static`, borrowed variables must outlive its [`Runnable`].
/// - If `schedule` is not [`Send`] and [`Sync`], all instances of the [`Runnable`]'s [`Waker`]
/// must be used and dropped on the original thread.
/// - If `schedule` is not `'static`, borrowed variables must outlive all instances of the
/// [`Runnable`]'s [`Waker`].
///
/// # Examples
///
/// ```
/// // The future inside the task.
/// let future = async {
/// println!("Hello, world!");
/// };
///
/// // If the task gets woken up, it will be sent into this channel.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with the future and the schedule function.
/// let (runnable, task) = unsafe { async_task::spawn_unchecked(future, schedule) };
/// ```
pub unsafe fn spawn_unchecked<F, S>(future: F, schedule: S) -> (Runnable, Task<F::Output>)
where
F: Future,
S: Schedule,
{
Builder::new().spawn_unchecked(move |()| future, schedule)
}
/// A handle to a runnable task.
///
/// Every spawned task has a single [`Runnable`] handle, which only exists when the task is
/// scheduled for running.
///
/// Method [`run()`][`Runnable::run()`] polls the task's future once. Then, the [`Runnable`]
/// vanishes and only reappears when its [`Waker`] wakes the task, thus scheduling it to be run
/// again.
///
/// Dropping a [`Runnable`] cancels the task, which means its future won't be polled again, and
/// awaiting the [`Task`] after that will result in a panic.
///
/// # Examples
///
/// ```
/// use async_task::Runnable;
/// use once_cell::sync::Lazy;
/// use std::{panic, thread};
///
/// // A simple executor.
/// static QUEUE: Lazy<flume::Sender<Runnable>> = Lazy::new(|| {
/// let (sender, receiver) = flume::unbounded::<Runnable>();
/// thread::spawn(|| {
/// for runnable in receiver {
/// let _ignore_panic = panic::catch_unwind(|| runnable.run());
/// }
/// });
/// sender
/// });
///
/// // Create a task with a simple future.
/// let schedule = |runnable| QUEUE.send(runnable).unwrap();
/// let (runnable, task) = async_task::spawn(async { 1 + 2 }, schedule);
///
/// // Schedule the task and await its output.
/// runnable.schedule();
/// assert_eq!(smol::future::block_on(task), 3);
/// ```
pub struct Runnable<M = ()> {
/// A pointer to the heap-allocated task.
pub(crate) ptr: NonNull<()>,
/// A marker capturing generic type `M`.
pub(crate) _marker: PhantomData<M>,
}
unsafe impl<M: Send + Sync> Send for Runnable<M> {}
unsafe impl<M: Send + Sync> Sync for Runnable<M> {}
#[cfg(feature = "std")]
impl<M> std::panic::UnwindSafe for Runnable<M> {}
#[cfg(feature = "std")]
impl<M> std::panic::RefUnwindSafe for Runnable<M> {}
impl<M> Runnable<M> {
/// Get the metadata associated with this task.
///
/// Tasks can be created with a metadata object associated with them; by default, this
/// is a `()` value. See the [`Builder::metadata()`] method for more information.
pub fn metadata(&self) -> &M {
&self.header().metadata
}
/// Schedules the task.
///
/// This is a convenience method that passes the [`Runnable`] to the schedule function.
///
/// # Examples
///
/// ```
/// // A function that schedules the task when it gets woken up.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with a simple future and the schedule function.
/// let (runnable, task) = async_task::spawn(async {}, schedule);
///
/// // Schedule the task.
/// assert_eq!(r.len(), 0);
/// runnable.schedule();
/// assert_eq!(r.len(), 1);
/// ```
pub fn schedule(self) {
let ptr = self.ptr.as_ptr();
let header = ptr as *const Header<M>;
mem::forget(self);
unsafe {
((*header).vtable.schedule)(ptr, ScheduleInfo::new(false));
}
}
/// Runs the task by polling its future.
///
/// Returns `true` if the task was woken while running, in which case the [`Runnable`] gets
/// rescheduled at the end of this method invocation. Otherwise, returns `false` and the
/// [`Runnable`] vanishes until the task is woken.
/// The return value is just a hint: `true` usually indicates that the task has yielded, i.e.
/// it woke itself and then gave the control back to the executor.
///
/// If the [`Task`] handle was dropped or if [`cancel()`][`Task::cancel()`] was called, then
/// this method simply destroys the task.
///
/// If the polled future panics, this method propagates the panic, and awaiting the [`Task`]
/// after that will also result in a panic.
///
/// # Examples
///
/// ```
/// // A function that schedules the task when it gets woken up.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with a simple future and the schedule function.
/// let (runnable, task) = async_task::spawn(async { 1 + 2 }, schedule);
///
/// // Run the task and check its output.
/// runnable.run();
/// assert_eq!(smol::future::block_on(task), 3);
/// ```
pub fn run(self) -> bool {
let ptr = self.ptr.as_ptr();
let header = ptr as *const Header<M>;
mem::forget(self);
unsafe { ((*header).vtable.run)(ptr) }
}
/// Returns a waker associated with this task.
///
/// # Examples
///
/// ```
/// use smol::future;
///
/// // A function that schedules the task when it gets woken up.
/// let (s, r) = flume::unbounded();
/// let schedule = move |runnable| s.send(runnable).unwrap();
///
/// // Create a task with a simple future and the schedule function.
/// let (runnable, task) = async_task::spawn(future::pending::<()>(), schedule);
///
/// // Take a waker and run the task.
/// let waker = runnable.waker();
/// runnable.run();
///
/// // Reschedule the task by waking it.
/// assert_eq!(r.len(), 0);
/// waker.wake();
/// assert_eq!(r.len(), 1);
/// ```
pub fn waker(&self) -> Waker {
let ptr = self.ptr.as_ptr();
let header = ptr as *const Header<M>;
unsafe {
let raw_waker = ((*header).vtable.clone_waker)(ptr);
Waker::from_raw(raw_waker)
}
}
fn header(&self) -> &Header<M> {
unsafe { &*(self.ptr.as_ptr() as *const Header<M>) }
}
/// Converts this task into a raw pointer.
///
/// To avoid a memory leak the pointer must be converted back to a Runnable using [`Runnable<M>::from_raw`][from_raw].
///
/// `into_raw` does not change the state of the [`Task`], but there is no guarantee that it will be in the same state after calling [`Runnable<M>::from_raw`][from_raw],
/// as the corresponding [`Task`] might have been dropped or cancelled.
///
/// # Examples
///
/// ```rust
/// use async_task::{Runnable, spawn};
/// let (runnable, task) = spawn(async {}, |_| {});
/// let runnable_pointer = runnable.into_raw();
///
/// unsafe {
/// // Convert back to an `Runnable` to prevent leak.
/// let runnable = Runnable::<()>::from_raw(runnable_pointer);
/// runnable.run();
/// // Further calls to `Runnable::from_raw(runnable_pointer)` would be memory-unsafe.
/// }
/// // The memory was freed when `x` went out of scope above, so `runnable_pointer` is now dangling!
/// ```
/// [from_raw]: #method.from_raw
pub fn into_raw(self) -> NonNull<()> {
let ptr = self.ptr;
mem::forget(self);
ptr
}
/// Converts a raw pointer into a Runnable.
///
/// # Safety
///
/// This method should only be used with raw pointers returned from [`Runnable<M>::into_raw`][into_raw].
/// It is not safe to use the provided pointer once it is passed to `from_raw`.
/// Crucially, it is unsafe to call `from_raw` multiple times with the same pointer - even if the resulting [`Runnable`] is not used -
/// as internally `async-task` uses reference counting.
///
/// It is however safe to call [`Runnable<M>::into_raw`][into_raw] on a [`Runnable`] created with `from_raw` or
/// after the [`Task`] associated with a given Runnable has been dropped or cancelled.
///
/// The state of the [`Runnable`] created with `from_raw` is not specified.
///
/// # Examples
///
/// ```rust
/// use async_task::{Runnable, spawn};
/// let (runnable, task) = spawn(async {}, |_| {});
/// let runnable_pointer = runnable.into_raw();
///
/// drop(task);
/// unsafe {
/// // Convert back to an `Runnable` to prevent leak.
/// let runnable = Runnable::<()>::from_raw(runnable_pointer);
/// let did_poll = runnable.run();
/// assert!(!did_poll);
/// // Further calls to `Runnable::from_raw(runnable_pointer)` would be memory-unsafe.
/// }
/// // The memory was freed when `x` went out of scope above, so `runnable_pointer` is now dangling!
/// ```
/// [into_raw]: #method.into_raw
pub unsafe fn from_raw(ptr: NonNull<()>) -> Self {
Self {
ptr,
_marker: Default::default(),
}
}
}
impl<M> Drop for Runnable<M> {
fn drop(&mut self) {
let ptr = self.ptr.as_ptr();
let header = self.header();
unsafe {
let mut state = header.state.load(Ordering::Acquire);
loop {
// If the task has been completed or closed, it can't be canceled.
if state & (COMPLETED | CLOSED) != 0 {
break;
}
// Mark the task as closed.
match header.state.compare_exchange_weak(
state,
state | CLOSED,
Ordering::AcqRel,
Ordering::Acquire,
) {
Ok(_) => break,
Err(s) => state = s,
}
}
// Drop the future.
(header.vtable.drop_future)(ptr);
// Mark the task as unscheduled.
let state = header.state.fetch_and(!SCHEDULED, Ordering::AcqRel);
// Notify the awaiter that the future has been dropped.
if state & AWAITER != 0 {
(*header).notify(None);
}
// Drop the task reference.
(header.vtable.drop_ref)(ptr);
}
}
}
impl<M: fmt::Debug> fmt::Debug for Runnable<M> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let ptr = self.ptr.as_ptr();
let header = ptr as *const Header<M>;
f.debug_struct("Runnable")
.field("header", unsafe { &(*header) })
.finish()
}
}