1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398
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 crate::header::Header;
use crate::raw::RawTask;
use crate::state::*;
use crate::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: Fn(Runnable) + 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: Fn(Runnable) + 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 {
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 = Checked {
id: thread_id(),
inner: ManuallyDrop::new(future),
};
unsafe { 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 `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`], the task's [`Waker`] must be used and dropped on
/// the original thread.
/// - If `schedule` is not `'static`, borrowed variables must outlive the task'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: Fn(Runnable),
{
// Allocate large futures on the heap.
let ptr = if mem::size_of::<F>() >= 2048 {
let future = alloc::boxed::Box::pin(future);
RawTask::<_, F::Output, S>::allocate(future, schedule)
} else {
RawTask::<F, F::Output, S>::allocate(future, schedule)
};
let runnable = Runnable { ptr };
let task = Task {
ptr,
_marker: PhantomData,
};
(runnable, task)
}
/// 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 {
/// A pointer to the heap-allocated task.
pub(crate) ptr: NonNull<()>,
}
unsafe impl Send for Runnable {}
unsafe impl Sync for Runnable {}
#[cfg(feature = "std")]
impl std::panic::UnwindSafe for Runnable {}
#[cfg(feature = "std")]
impl std::panic::RefUnwindSafe for Runnable {}
impl Runnable {
/// 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;
mem::forget(self);
unsafe {
((*header).vtable.schedule)(ptr);
}
}
/// 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;
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;
unsafe {
let raw_waker = ((*header).vtable.clone_waker)(ptr);
Waker::from_raw(raw_waker)
}
}
}
impl Drop for Runnable {
fn drop(&mut self) {
let ptr = self.ptr.as_ptr();
let header = ptr as *const 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 fmt::Debug for Runnable {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let ptr = self.ptr.as_ptr();
let header = ptr as *const Header;
f.debug_struct("Runnable")
.field("header", unsafe { &(*header) })
.finish()
}
}