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//! Async executor. //! //! This crate offers two kinds of executors: single-threaded and multi-threaded. //! //! # Examples //! //! Run a single-threaded and a multi-threaded executor at the same time: //! //! ``` //! use async_channel::unbounded; //! use async_executor::{Executor, LocalExecutor}; //! use easy_parallel::Parallel; //! //! let ex = Executor::new(); //! let local_ex = LocalExecutor::new(); //! let (trigger, shutdown) = unbounded::<()>(); //! //! Parallel::new() //! // Run four executor threads. //! .each(0..4, |_| ex.run(shutdown.recv())) //! // Run local executor on the current thread. //! .finish(|| local_ex.run(async { //! println!("Hello world!"); //! drop(trigger); //! })); //! ``` #![forbid(unsafe_code)] #![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)] use std::future::Future; use std::pin::Pin; use std::task::{Context, Poll}; use std::time::Duration; use futures_lite::pin; use scoped_tls::scoped_thread_local; use waker_fn::waker_fn; #[cfg(feature = "async-io")] use async_io::parking; #[cfg(not(feature = "async-io"))] use parking; scoped_thread_local!(static EX: Executor); scoped_thread_local!(static LOCAL_EX: LocalExecutor); /// Multi-threaded executor. /// /// The executor does not spawn threads on its own. Instead, you need to call [`Executor::run()`] /// on manually spawned executor threads. /// /// # Examples /// /// ``` /// 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, |_| ex.run(shutdown.recv())) /// // Run the main future on the current thread. /// .finish(|| future::block_on(async { /// println!("Hello world!"); /// drop(signal); /// })); /// ``` #[derive(Debug)] pub struct Executor { ex: multitask::Executor, } impl Executor { /// Creates a multi-threaded executor. /// /// # Examples /// /// ``` /// use async_executor::LocalExecutor; /// /// let local_ex = LocalExecutor::new(); /// ``` pub fn new() -> Executor { Executor { ex: multitask::Executor::new(), } } /// 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 + 'static>( &self, future: impl Future<Output = T> + Send + 'static, ) -> Task<T> { Task(self.ex.spawn(future)) } /// Enters the context of an executor. /// /// # Examples /// /// ``` /// use async_executor::{Executor, Task}; /// /// let ex = Executor::new(); /// /// ex.enter(|| { /// // `Task::spawn()` now knows which executor to spawn onto. /// let task = Task::spawn(async { /// println!("Hello world"); /// }); /// }); /// ``` pub fn enter<T>(&self, f: impl FnOnce() -> T) -> T { if EX.is_set() { panic!("cannot call `Executor::enter()` if already inside an `Executor`"); } EX.set(self, f) } /// Runs the executor until the given future completes. /// /// # Examples /// /// ``` /// use async_executor::Executor; /// /// let ex = Executor::new(); /// /// let task = ex.spawn(async { 1 + 2 }); /// let res = ex.run(async { task.await * 2 }); /// /// assert_eq!(res, 6); /// ``` pub fn run<T>(&self, future: impl Future<Output = T>) -> T { self.enter(|| { let (p, u) = parking::pair(); let ticker = self.ex.ticker({ let u = u.clone(); move || u.unpark() }); pin!(future); let waker = waker_fn(move || u.unpark()); let cx = &mut Context::from_waker(&waker); 'start: loop { if let Poll::Ready(t) = future.as_mut().poll(cx) { break t; } for _ in 0..200 { if !ticker.tick() { p.park(); continue 'start; } } p.park_timeout(Duration::from_secs(0)); } }) } } impl Default for Executor { fn default() -> Executor { Executor::new() } } /// Single-threaded executor. /// /// The executor can only be run on the thread that created it. /// /// # Examples /// /// ``` /// use async_executor::LocalExecutor; /// /// let local_ex = LocalExecutor::new(); /// /// local_ex.run(async { /// println!("Hello world!"); /// }); /// ``` #[derive(Debug)] pub struct LocalExecutor { ex: multitask::LocalExecutor, parker: parking::Parker, } impl LocalExecutor { /// Creates a single-threaded executor. /// /// # Examples /// /// ``` /// use async_executor::LocalExecutor; /// /// let local_ex = LocalExecutor::new(); /// ``` pub fn new() -> LocalExecutor { let (p, u) = parking::pair(); LocalExecutor { ex: multitask::LocalExecutor::new(move || u.unpark()), parker: p, } } /// 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: 'static>(&self, future: impl Future<Output = T> + 'static) -> Task<T> { Task(self.ex.spawn(future)) } /// Runs the executor until the given future completes. /// /// # Examples /// /// ``` /// use async_executor::LocalExecutor; /// /// let local_ex = LocalExecutor::new(); /// /// let task = local_ex.spawn(async { 1 + 2 }); /// let res = local_ex.run(async { task.await * 2 }); /// /// assert_eq!(res, 6); /// ``` pub fn run<T>(&self, future: impl Future<Output = T>) -> T { pin!(future); let u = self.parker.unparker(); let waker = waker_fn(move || u.unpark()); let cx = &mut Context::from_waker(&waker); LOCAL_EX.set(self, || { 'start: loop { if let Poll::Ready(t) = future.as_mut().poll(cx) { break t; } for _ in 0..200 { if !self.ex.tick() { self.parker.park(); continue 'start; } } self.parker.park_timeout(Duration::from_secs(0)); } }) } } impl Default for LocalExecutor { fn default() -> LocalExecutor { LocalExecutor::new() } } /// 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. /// /// # Examples /// /// ``` /// use async_executor::{Executor, Task}; /// /// let ex = Executor::new(); /// /// ex.run(async { /// let task = Task::spawn(async { /// println!("Hello from a task!"); /// 1 + 2 /// }); /// /// assert_eq!(task.await, 3); /// }); /// ``` #[must_use = "tasks get canceled when dropped, use `.detach()` to run them in the background"] #[derive(Debug)] pub struct Task<T>(multitask::Task<T>); impl<T> Task<T> { /// Spawns a task onto the current multi-threaded or single-threaded executor. /// /// If called from an [`Executor`] (preferred) or from a [`LocalExecutor`], the task is spawned /// on it. /// /// Otherwise, this method panics. /// /// # Examples /// /// ``` /// use async_executor::{Executor, Task}; /// /// let ex = Executor::new(); /// /// ex.run(async { /// let task = Task::spawn(async { 1 + 2 }); /// assert_eq!(task.await, 3); /// }); /// ``` /// /// ``` /// use async_executor::{LocalExecutor, Task}; /// /// let local_ex = LocalExecutor::new(); /// /// local_ex.run(async { /// let task = Task::spawn(async { 1 + 2 }); /// assert_eq!(task.await, 3); /// }); /// ``` pub fn spawn(future: impl Future<Output = T> + Send + 'static) -> Task<T> where T: Send + 'static, { if EX.is_set() { EX.with(|ex| ex.spawn(future)) } else if LOCAL_EX.is_set() { LOCAL_EX.with(|local_ex| local_ex.spawn(future)) } else { panic!("`Task::spawn()` must be called from an `Executor` or `LocalExecutor`") } } /// Spawns a task onto the current single-threaded executor. /// /// If called from a [`LocalExecutor`], the task is spawned on it. /// /// Otherwise, this method panics. /// /// # Examples /// /// ``` /// use async_executor::{LocalExecutor, Task}; /// /// let local_ex = LocalExecutor::new(); /// /// local_ex.run(async { /// let task = Task::local(async { 1 + 2 }); /// assert_eq!(task.await, 3); /// }); /// ``` pub fn local(future: impl Future<Output = T> + 'static) -> Task<T> where T: 'static, { if LOCAL_EX.is_set() { LOCAL_EX.with(|local_ex| local_ex.spawn(future)) } else { panic!("`Task::local()` must be called from a `LocalExecutor`") } } /// Detaches the task to let it keep running in the background. /// /// # Examples /// /// ``` /// use async_executor::{Executor, Task}; /// use futures_lite::future; /// /// let ex = Executor::new(); /// /// ex.spawn(async { /// loop { /// println!("I'm a background task looping forever."); /// future::yield_now().await; /// } /// }) /// .detach(); /// /// ex.run(future::yield_now()); /// ``` pub fn detach(self) { self.0.detach(); } /// 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, Task}; /// use futures_lite::future; /// /// let ex = Executor::new(); /// /// let task = ex.spawn(async { /// loop { /// println!("Even though I'm in an infinite loop, you can still cancel me!"); /// future::yield_now().await; /// } /// }); /// /// ex.run(async { /// task.cancel().await; /// }); /// ``` pub async fn cancel(self) -> Option<T> { self.0.cancel().await } } impl<T> Future for Task<T> { type Output = T; fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { Pin::new(&mut self.0).poll(cx) } }