Struct Task

pub struct Task<T> { /* private fields */ }

A spawned task.

A Task can be awaited to retrieve the output of its future.

Dropping a Task cancels it, which means its future won’t be polled again. To drop the Task handle without canceling it, use detach() instead. To cancel a task gracefully and wait until it is fully destroyed, use the cancel() method.

Note that canceling a task actually wakes it and reschedules one last time. Then, the executor can destroy the task by simply dropping its Runnable or by invoking [run()][super::Runnable:: run()].

Examples

use smol::{future, Executor};
use std::thread;

let ex = Executor::new();

// Spawn a future onto the executor.
let task = ex.spawn(async {
    println!("Hello from a task!");
    1 + 2
});

// Run an executor thread.
thread::spawn(move || future::block_on(ex.run(future::pending::<()>())));

// Wait for the task's output.
assert_eq!(future::block_on(task), 3);

Implementations

impl<T> Task<T>

pub fn detach(self)

Detaches the task to let it keep running in the background.

Examples

use smol::{Executor, Timer};
use std::time::Duration;

let ex = Executor::new();

// Spawn a deamon future.
ex.spawn(async {
    loop {
        println!("I'm a daemon task looping forever.");
        Timer::after(Duration::from_secs(1)).await;
    }
})
.detach();

pub async fn cancel(self) -> Option<T>

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 smol::{future, Executor, Timer};
use std::thread;
use std::time::Duration;

let ex = Executor::new();

// Spawn a deamon future.
let task = ex.spawn(async {
    loop {
        println!("Even though I'm in an infinite loop, you can still cancel me!");
        Timer::after(Duration::from_secs(1)).await;
    }
});

// Run an executor thread.
thread::spawn(move || future::block_on(ex.run(future::pending::<()>())));

future::block_on(async {
    Timer::after(Duration::from_secs(3)).await;
    task.cancel().await;
});

pub fn into_raw(self) -> *mut ()

Consumes the Task, returning a pointer to the raw task.

The raw pointer must eventually be converted back into a Task by calling Task::from_raw in order to free up its resources.

pub unsafe fn from_raw(ptr: *mut ()) -> Task<T>

Constructs a Task from a raw task pointer.

The raw pointer must have been previously returned by a call to [into_raw].

Safety

See above.

Trait Implementations

impl<T> Debug for Task<T>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<T> Drop for Task<T>

fn drop(&mut self)

Executes the destructor for this type.

impl<T> Future for Task<T>

type Output = T

The type of value produced on completion.

fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>

Attempts to resolve the future to a final value, registering the current task for wakeup if the value is not yet available.

impl<T> RefUnwindSafe for Task<T>

impl<T: Send> Send for Task<T>

impl<T> Sync for Task<T>

impl<T> Unpin for Task<T>

impl<T> UnwindSafe for Task<T>