Struct tokio::task::JoinSet

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

Available on crate feature rt only.

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.

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_next().await {
        let idx = res.unwrap();
        seen[idx] = true;
    }

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

Implementations

impl<T> JoinSet<T>

pub fn new() -> Self

Create a new JoinSet.

pub fn len(&self) -> usize

Returns the number of tasks currently in the JoinSet.

pub fn is_empty(&self) -> bool

Returns whether the JoinSet is empty.

impl<T: 'static> JoinSet<T>

pub fn build_task(&mut self) -> Builder<'_, T>

Available on tokio_unstable and crate feature tracing only.

Returns a Builder that can be used to configure a task prior to spawning it on this JoinSet.

Examples

use tokio::task::JoinSet;

#[tokio::main]
async fn main() -> std::io::Result<()> {
    let mut set = JoinSet::new();

    // Use the builder to configure a task's name before spawning it.
    set.build_task()
        .name("my_task")
        .spawn(async { /* ... */ })?;

    Ok(())
}

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

Spawn the provided task on the JoinSet, returning an AbortHandle that can be used to remotely cancel the task.

The provided future will start running in the background immediately when this method is called, even if you don’t await anything on this JoinSet.

Panics

This method panics if called outside of a Tokio runtime.

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

Spawn the provided task on the provided runtime and store it in this JoinSet returning an AbortHandle that can be used to remotely cancel the task.

The provided future will start running in the background immediately when this method is called, even if you don’t await anything on this JoinSet.

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

Spawn the provided task on the current LocalSet and store it in this JoinSet, returning an AbortHandle that can be used to remotely cancel the task.

The provided future will start running in the background immediately when this method is called, even if you don’t await anything on 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 ) -> AbortHandlewhere F: Future<Output = T> + 'static,

Spawn the provided task on the provided LocalSet and store it in this JoinSet, returning an AbortHandle that can be used to remotely cancel the task.

Unlike the spawn_local method, this method may be used to spawn local tasks on a LocalSet that is not currently running. The provided future will start running whenever the LocalSet is next started.

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

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_next 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 join_next_with_id(&mut self) -> Option<Result<(Id, T), JoinError>>

Available on tokio_unstable only.

Waits until one of the tasks in the set completes and returns its output, along with the task ID of the completed task.

Returns None if the set is empty.

When this method returns an error, then the id of the task that failed can be accessed using the JoinError::id method.

Cancel Safety

This method is cancel safe. If join_next_with_id 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)

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

Calling this method is equivalent to calling abort_all and then calling join_next in a loop until it returns 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)

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_next in a loop until the JoinSet is empty.

pub fn detach_all(&mut self)

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>

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

Formats the value using the given formatter.

impl<T> Default for JoinSet<T>

fn default() -> Self

Returns the “default value” for a type.

impl<T> Drop for JoinSet<T>

fn drop(&mut self)

Executes the destructor for this type.