Struct tokio::task::JoinSet

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

Expand description

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

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impl<T> JoinSet<T>

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pub fn new() -> Self

Create a new JoinSet.

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pub fn len(&self) -> usize

Returns the number of tasks currently in the JoinSet.

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pub fn is_empty(&self) -> bool

Returns whether the JoinSet is empty.

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impl<T: 'static> JoinSet<T>

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

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

You do not have to .await the returned JoinHandle to make the provided future start execution. It will start running in the background immediately when spawn is called.

Panics

This method panics if called outside of a Tokio runtime.

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pub fn spawn_on<F>(&mut self, task: F, handle: &Handle) -> AbortHandlewhere
 F: Future<Output = T>,
 F: 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.

You do not have to .await the returned JoinHandle to make the provided future start execution. It will start running in the background immediately when spawn_on is called.

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

You do not have to .await the returned JoinHandle to make the provided future start execution. It will start running in the background immediately when spawn_local is called.

Panics

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

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pub fn spawn_local_on<F>(&mut self, task: F, local_set: &LocalSet) -> AbortHandlewhere
F: Future<Output = T>,
F: '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 when the LocalSet is not running. You do not have to .await the returned JoinHandle to make the provided future start execution. It will start running immediately whenever the LocalSet is next started.

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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.

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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.

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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.

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