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#![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#![doc(
75 html_favicon_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
76)]
77#![doc(
78 html_logo_url = "https://raw.githubusercontent.com/smol-rs/smol/master/assets/images/logo_fullsize_transparent.png"
79)]
80
81extern crate alloc;
82#[cfg(feature = "std")]
83extern crate std;
84
85/// We can't use `?` in const contexts yet, so this macro acts
86/// as a workaround.
87macro_rules! leap {
88 ($x: expr) => {{
89 match ($x) {
90 Some(val) => val,
91 None => return None,
92 }
93 }};
94}
95
96macro_rules! leap_unwrap {
97 ($x: expr) => {{
98 match ($x) {
99 Some(val) => val,
100 None => panic!("called `Option::unwrap()` on a `None` value"),
101 }
102 }};
103}
104
105mod header;
106mod raw;
107mod runnable;
108mod state;
109mod task;
110mod utils;
111
112pub use crate::runnable::{
113 spawn, spawn_unchecked, Builder, Runnable, Schedule, ScheduleInfo, WithInfo,
114};
115pub use crate::task::{FallibleTask, Task};
116
117#[cfg(feature = "std")]
118pub use crate::runnable::spawn_local;
119