async_task/
lib.rs

1//! Task abstraction for building executors.
2//!
3//! To spawn a future onto an executor, we first need to allocate it on the heap and keep some
4//! state attached to it. The state indicates whether the future is ready for polling, waiting to
5//! be woken up, or completed. Such a stateful future is called a *task*.
6//!
7//! All executors have a queue that holds scheduled tasks:
8//!
9//! ```
10//! let (sender, receiver) = flume::unbounded();
11//! #
12//! # // A future that will get spawned.
13//! # let future = async { 1 + 2 };
14//! #
15//! # // A function that schedules the task when it gets woken up.
16//! # let schedule = move |runnable| sender.send(runnable).unwrap();
17//! #
18//! # // Create a task.
19//! # let (runnable, task) = async_task::spawn(future, schedule);
20//! ```
21//!
22//! A task is created using either [`spawn()`], [`spawn_local()`], or [`spawn_unchecked()`] which
23//! return a [`Runnable`] and a [`Task`]:
24//!
25//! ```
26//! # let (sender, receiver) = flume::unbounded();
27//! #
28//! // A future that will be spawned.
29//! let future = async { 1 + 2 };
30//!
31//! // A function that schedules the task when it gets woken up.
32//! let schedule = move |runnable| sender.send(runnable).unwrap();
33//!
34//! // Construct a task.
35//! let (runnable, task) = async_task::spawn(future, schedule);
36//!
37//! // Push the task into the queue by invoking its schedule function.
38//! runnable.schedule();
39//! ```
40//!
41//! The [`Runnable`] is used to poll the task's future, and the [`Task`] is used to await its
42//! output.
43//!
44//! Finally, we need a loop that takes scheduled tasks from the queue and runs them:
45//!
46//! ```no_run
47//! # let (sender, receiver) = flume::unbounded();
48//! #
49//! # // A future that will get spawned.
50//! # let future = async { 1 + 2 };
51//! #
52//! # // A function that schedules the task when it gets woken up.
53//! # let schedule = move |runnable| sender.send(runnable).unwrap();
54//! #
55//! # // Create a task.
56//! # let (runnable, task) = async_task::spawn(future, schedule);
57//! #
58//! # // Push the task into the queue by invoking its schedule function.
59//! # runnable.schedule();
60//! #
61//! for runnable in receiver {
62//!     runnable.run();
63//! }
64//! ```
65//!
66//! Method [`run()`][`Runnable::run()`] polls the task's future once. Then, the [`Runnable`]
67//! vanishes and only reappears when its [`Waker`][`core::task::Waker`] wakes the task, thus
68//! scheduling it to be run again.
69
70#![cfg_attr(not(feature = "std"), no_std)]
71#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
72#![doc(test(attr(deny(rust_2018_idioms, warnings))))]
73#![doc(test(attr(allow(unused_extern_crates, unused_variables))))]
74
75extern crate alloc;
76
77mod header;
78mod raw;
79mod runnable;
80mod state;
81mod task;
82mod utils;
83
84pub use crate::runnable::{spawn, spawn_unchecked, Runnable};
85pub use crate::task::Task;
86
87#[cfg(feature = "std")]
88pub use crate::runnable::spawn_local;