Struct tokio::task::JoinSet

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

A collection of tasks spawned on a Tokio runtime.

A JoinSet can be used to await the completion of some or all of the tasks in the set. The set is not ordered, and the tasks will be returned in the order they complete.

All of the tasks must have the same return type T.

When the JoinSet is dropped, all tasks in the JoinSet are immediately aborted.

Note: This is an unstable API. The public API of this type may break in 1.x releases. See the documentation on unstable features for details.

Examples

Spawn multiple tasks and wait for them.

use tokio::task::JoinSet;

#[tokio::main]
async fn main() {
    let mut set = JoinSet::new();

    for i in 0..10 {
        set.spawn(async move { i });
    }

    let mut seen = [false; 10];
    while let Some(res) = set.join_one().await.unwrap() {
        seen[res] = true;
    }

    for i in 0..10 {
        assert!(seen[i]);
    }
}

Implementations

impl<T> JoinSet<T>

pub fn new() -> Self

This is supported on tokio_unstable only.

Create a new JoinSet.

pub fn len(&self) -> usize

This is supported on tokio_unstable only.

Returns the number of tasks currently in the JoinSet.

pub fn is_empty(&self) -> bool

This is supported on tokio_unstable only.

Returns whether the JoinSet is empty.

impl<T: 'static> JoinSet<T>

pub fn spawn<F>(&mut self, task: F) where
    F: Future<Output = T>,
    F: Send + 'static,
    T: Send, 

This is supported on tokio_unstable only.

Spawn the provided task on the JoinSet.

Panics

This method panics if called outside of a Tokio runtime.

pub fn spawn_on<F>(&mut self, task: F, handle: &Handle) where
    F: Future<Output = T>,
    F: Send + 'static,
    T: Send, 

This is supported on tokio_unstable only.

Spawn the provided task on the provided runtime and store it in this JoinSet.

pub fn spawn_local<F>(&mut self, task: F) where
    F: Future<Output = T>,
    F: 'static, 

This is supported on tokio_unstable only.

Spawn the provided task on the current LocalSet and store it in this JoinSet.

Panics

This method panics if it is called outside of a LocalSet.

pub fn spawn_local_on<F>(&mut self, task: F, local_set: &LocalSet) where
    F: Future<Output = T>,
    F: 'static, 

This is supported on tokio_unstable only.

Spawn the provided task on the provided LocalSet and store it in this JoinSet.

pub async fn join_one(&mut self) -> Result<Option<T>, JoinError>

This is supported on tokio_unstable only.

Waits until one of the tasks in the set completes and returns its output.

Returns None if the set is empty.

Cancel Safety

This method is cancel safe. If join_one is used as the event in a tokio::select! statement and some other branch completes first, it is guaranteed that no tasks were removed from this JoinSet.

pub async fn shutdown(&mut self)

This is supported on tokio_unstable only.

Aborts all tasks and waits for them to finish shutting down.

Calling this method is equivalent to calling abort_all and then calling join_one in a loop until it returns Ok(None).

This method ignores any panics in the tasks shutting down. When this call returns, the JoinSet will be empty.

pub fn abort_all(&mut self)

This is supported on tokio_unstable only.

Aborts all tasks on this JoinSet.

This does not remove the tasks from the JoinSet. To wait for the tasks to complete cancellation, you should call join_one in a loop until the JoinSet is empty.

pub fn detach_all(&mut self)

This is supported on tokio_unstable only.

Removes all tasks from this JoinSet without aborting them.

The tasks removed by this call will continue to run in the background even if the JoinSet is dropped.

Trait Implementations

impl<T> Debug for JoinSet<T>

This is supported on tokio_unstable only.

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

Formats the value using the given formatter.

impl<T> Default for JoinSet<T>

This is supported on tokio_unstable only.

fn default() -> Self

Returns the “default value” for a type.

impl<T> Drop for JoinSet<T>

This is supported on tokio_unstable only.

fn drop(&mut self)

Executes the destructor for this type.