impl CancellationToken

fn new() -> CancellationToken

Creates a new CancellationToken in the non-cancelled state.

fn child_token(&self) -> CancellationToken

Creates a CancellationToken which will get cancelled whenever the current token gets cancelled. Unlike a cloned CancellationToken, cancelling a child token does not cancel the parent token.

If the current token is already cancelled, the child token will get returned in cancelled state.

Examples

use tokio::select;
use tokio_util::sync::CancellationToken;

#[tokio::main]
async fn main() {
    let token = CancellationToken::new();
    let child_token = token.child_token();

    let join_handle = tokio::spawn(async move {
        // Wait for either cancellation or a very long time
        select! {
            _ = child_token.cancelled() => {
                // The token was cancelled
                5
            }
            _ = tokio::time::sleep(std::time::Duration::from_secs(9999)) => {
                99
            }
        }
    });

    tokio::spawn(async move {
        tokio::time::sleep(std::time::Duration::from_millis(10)).await;
        token.cancel();
    });

    assert_eq!(5, join_handle.await.unwrap());
}

fn cancel(&self)

Cancel the CancellationToken and all child tokens which had been derived from it.

This will wake up all tasks which are waiting for cancellation.

Be aware that cancellation is not an atomic operation. It is possible for another thread running in parallel with a call to cancel to first receive true from is_cancelled on one child node, and then receive false from is_cancelled on another child node. However, once the call to cancel returns, all child nodes have been fully cancelled.

fn is_cancelled(&self) -> bool

Returns true if the CancellationToken is cancelled.

fn cancelled(&self) -> WaitForCancellationFuture<'_>

Returns a Future that gets fulfilled when cancellation is requested.

Equivalent to:

async fn cancelled(&self);

The future will complete immediately if the token is already cancelled when this method is called.

Cancellation safety

This method is cancel safe.

fn cancelled_owned(self) -> WaitForCancellationFutureOwned

Returns a Future that gets fulfilled when cancellation is requested.

Equivalent to:

async fn cancelled_owned(self);

The future will complete immediately if the token is already cancelled when this method is called.

The function takes self by value and returns a future that owns the token.

Cancellation safety

This method is cancel safe.

fn drop_guard(self) -> DropGuard

Creates a DropGuard for this token.

Returned guard will cancel this token (and all its children) on drop unless disarmed.

fn drop_guard_ref(&self) -> DropGuardRef<'_>

Creates a DropGuardRef for this token.

Returned guard will cancel this token (and all its children) on drop unless disarmed.

async fn run_until_cancelled<F>(&self, fut: F) -> Option<F::Output>
where
    F: Future,

Runs a future to completion and returns its result wrapped inside of an Option unless the CancellationToken is cancelled. In that case the function returns None and the future gets dropped.

Fairness

Calling this on an already-cancelled token directly returns None. For all subsequent polls, in case of concurrent completion and cancellation, this is biased towards the future completion.

Cancellation safety

This method is only cancel safe if fut is cancel safe.

async fn run_until_cancelled_owned<F>(self, fut: F) -> Option<F::Output>
where
    F: Future,

Runs a future to completion and returns its result wrapped inside of an Option unless the CancellationToken is cancelled. In that case the function returns None and the future gets dropped.

The function takes self by value and returns a future that owns the token.

Fairness

Calling this on an already-cancelled token directly returns None. For all subsequent polls, in case of concurrent completion and cancellation, this is biased towards the future completion.

Cancellation safety

This method is only cancel safe if fut is cancel safe.