Struct async_task::Runnable
source · pub struct Runnable<M = ()> { /* private fields */ }Expand description
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() 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);Implementations§
source§impl<M> Runnable<M>
impl<M> Runnable<M>
sourcepub fn metadata(&self) -> &M
pub fn metadata(&self) -> &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.
sourcepub fn schedule(self)
pub fn schedule(self)
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);sourcepub fn run(self) -> bool
pub fn run(self) -> bool
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() 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);sourcepub fn waker(&self) -> Waker
pub fn waker(&self) -> Waker
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);