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Struct tauri::async_runtime::TokioJoinHandle

pub struct TokioJoinHandle<T> { /* fields omitted */ }

Expand description

An owned permission to join on a task (await its termination).

This can be thought of as the equivalent of std::thread::JoinHandle for a task rather than a thread.

A JoinHandle detaches the associated task when it is dropped, which means that there is no longer any handle to the task, and no way to join on it.

This struct is created by the task::spawn and task::spawn_blocking functions.

Examples#

Creation from task::spawn:

use tokio::task;

let join_handle: task::JoinHandle<_> = task::spawn(async {
    // some work here
});

Creation from task::spawn_blocking:

use tokio::task;

let join_handle: task::JoinHandle<_> = task::spawn_blocking(|| {
    // some blocking work here
});

The generic parameter T in JoinHandle<T> is the return type of the spawned task. If the return value is an i32, the join handle has type JoinHandle<i32>:

use tokio::task;

let join_handle: task::JoinHandle<i32> = task::spawn(async {
    5 + 3
});

If the task does not have a return value, the join handle has type JoinHandle<()>:

use tokio::task;

let join_handle: task::JoinHandle<()> = task::spawn(async {
    println!("I return nothing.");
});

Note that handle.await doesn’t give you the return type directly. It is wrapped in a Result because panics in the spawned task are caught by Tokio. The ? operator has to be double chained to extract the returned value:

use tokio::task;
use std::io;

#[tokio::main]

async fn main() -> io::Result<()> {
    let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
        Ok(5 + 3)
    });

    let result = join_handle.await??;
    assert_eq!(result, 8);
    Ok(())
}

If the task panics, the error is a JoinError that contains the panic:

use tokio::task;
use std::io;
use std::panic;

#[tokio::main]

async fn main() -> io::Result<()> {
    let join_handle: task::JoinHandle<Result<i32, io::Error>> = tokio::spawn(async {
        panic!("boom");
    });

    let err = join_handle.await.unwrap_err();
    assert!(err.is_panic());
    Ok(())
}

Child being detached and outliving its parent:

use tokio::task;
use tokio::time;
use std::time::Duration;

let original_task = task::spawn(async {
    let _detached_task = task::spawn(async {
        // Here we sleep to make sure that the first task returns before.
        time::sleep(Duration::from_millis(10)).await;
        // This will be called, even though the JoinHandle is dropped.
        println!("♫ Still alive ♫");
    });
});

original_task.await.expect("The task being joined has panicked");
println!("Original task is joined.");

// We make sure that the new task has time to run, before the main
// task returns.

time::sleep(Duration::from_millis(1000)).await;

Implementations#

impl<T> JoinHandle<T>#

pub fn abort(&self)#

Abort the task associated with the handle.

Awaiting a cancelled task might complete as usual if the task was already completed at the time it was cancelled, but most likely it will complete with a Err(JoinError::Cancelled).

use tokio::time;

#[tokio::main]

async fn main() {
   let mut handles = Vec::new();

   handles.push(tokio::spawn(async {
      time::sleep(time::Duration::from_secs(10)).await;
      true
   }));

   handles.push(tokio::spawn(async {
      time::sleep(time::Duration::from_secs(10)).await;
      false
   }));

   for handle in &handles {
       handle.abort();
   }

   for handle in handles {
       assert!(handle.await.unwrap_err().is_cancelled());
   }
}

Trait Implementations#

impl<T> Debug for JoinHandle<T> where T: Debug,#

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

Formats the value using the given formatter. Read more

impl<T> Drop for JoinHandle<T>#

pub fn drop(&mut self)#

Executes the destructor for this type. Read more

impl<T> Future for JoinHandle<T>#

type Output = Result<T, JoinError>#

The type of value produced on completion.

pub fn poll( self: Pin<&mut JoinHandle<T>>, cx: &mut Context<'_> ) -> Poll<<JoinHandle<T> as Future>::Output>#

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

impl<T> Send for JoinHandle<T> where T: Send,#

impl<T> Sync for JoinHandle<T> where T: Send,#

impl<T> Unpin for JoinHandle<T>#

Auto Trait Implementations#

impl<T> \!RefUnwindSafe for JoinHandle<T>#

impl<T> \!UnwindSafe for JoinHandle<T>#

Blanket Implementations#

impl<T> Any for T where T: 'static + ?Sized,[src]#

pub fn type_id(&self) -> TypeId[src]#

Gets the TypeId of self. Read more

impl<T> Borrow<T> for T where T: ?Sized,[src]#

pub fn borrow(&self) -> &T[src]#

Immutably borrows from an owned value. Read more

impl<T> BorrowMut<T> for T where T: ?Sized,[src]#

pub fn borrow_mut(&mut self) -> &mutT[src]#

Mutably borrows from an owned value. Read more

impl<T> From<T> for T[src]#

pub fn from(t: T) -> T[src]#

Performs the conversion.

impl<F> FutureExt for F where F: Future + ?Sized,#

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

A convenience for calling Future::poll() on !Unpin types.

fn or<F>(self, other: F) -> Or<Self, F> where F: Future<Output = Self::Output>,#

Returns the result of self or other future, preferring self if both are ready. Read more

fn race<F>(self, other: F) -> Race<Self, F> where F: Future<Output = Self::Output>,#

Returns the result of self or other future, with no preference if both are ready. Read more

fn catch_unwind(self) -> CatchUnwind<Self> where Self: UnwindSafe,#

Catches panics while polling the future. Read more

fn boxed<'a>( self ) -> Pin<Box<dyn Future<Output = Self::Output> + 'a + Send, Global>> where Self: Send + 'a,#

Boxes the future and changes its type to dyn Future + Send + 'a. Read more

fn boxed_local<'a>( self ) -> Pin<Box<dyn Future<Output = Self::Output> + 'a, Global>> where Self: 'a,#

Boxes the future and changes its type to dyn Future + 'a. Read more

impl<T> FutureExt for T where T: Future + ?Sized,#

fn map<U, F>(self, f: F) -> Map<Self, F> where F: FnOnce(Self::Output) -> U,#

Map this future’s output to a different type, returning a new future of the resulting type. Read more

fn map_into<U>(self) -> MapInto<Self, U> where Self::Output: Into<U>,#

Map this future’s output to a different type, returning a new future of the resulting type. Read more

fn then<Fut, F>(self, f: F) -> Then<Self, Fut, F> where F: FnOnce(Self::Output) -> Fut, Fut: Future,#

Chain on a computation for when a future finished, passing the result of the future to the provided closure f. Read more

fn left_future<B>(self) -> Either<Self, B> where B: Future<Output = Self::Output>,#

Wrap this future in an Either future, making it the left-hand variant of that Either. Read more

fn right_future<A>(self) -> Either<A, Self> where A: Future<Output = Self::Output>,#

Wrap this future in an Either future, making it the right-hand variant of that Either. Read more

fn into_stream(self) -> IntoStream<Self>#

Convert this future into a single element stream. Read more

fn flatten(self) -> Flatten<Self> where Self::Output: Future,#

Flatten the execution of this future when the output of this future is itself another future. Read more

fn flatten_stream(self) -> FlattenStream<Self> where Self::Output: Stream,#

Flatten the execution of this future when the successful result of this future is a stream. Read more

fn fuse(self) -> Fuse<Self>#

Fuse a future such that poll will never again be called once it has completed. This method can be used to turn any Future into a FusedFuture. Read more

fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnOnce(&Self::Output),#

Do something with the output of a future before passing it on. Read more

fn catch_unwind(self) -> CatchUnwind<Self> where Self: UnwindSafe,#

Catches unwinding panics while polling the future. Read more

fn shared(self) -> Shared<Self> where Self::Output: Clone,#

Create a cloneable handle to this future where all handles will resolve to the same result. Read more

fn remote_handle(self) -> (Remote<Self>, RemoteHandle<Self::Output>)#

Turn this future into a future that yields () on completion and sends its output to another future on a separate task. Read more

fn boxed<'a>( self ) -> Pin<Box<dyn Future<Output = Self::Output> + 'a + Send, Global>> where Self: Send + 'a,#

Wrap the future in a Box, pinning it. Read more

fn boxed_local<'a>( self ) -> Pin<Box<dyn Future<Output = Self::Output> + 'a, Global>> where Self: 'a,#

Wrap the future in a Box, pinning it. Read more

fn unit_error(self) -> UnitError<Self>#

Turns a Future<Output = T> into a TryFuture<Ok = T, Error = ()>. Read more

fn never_error(self) -> NeverError<Self>#

Turns a Future<Output = T> into a TryFuture<Ok = T, Error = Never>. Read more

fn poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Self::Output> where Self: Unpin,#

A convenience for calling Future::poll on Unpin future types.

fn now_or_never(self) -> Option<Self::Output>#

Evaluates and consumes the future, returning the resulting output if the future is ready after the first call to Future::poll. Read more

impl<T, U> Into<U> for T where U: From<T>,[src]#

pub fn into(self) -> U[src]#

Performs the conversion.

impl<F> IntoFuture for F where F: Future,[src]#

type Output = <F as Future>::Output#

🔬 This is a nightly-only experimental API. (into_future)

The output that the future will produce on completion.

type Future = F#

🔬 This is a nightly-only experimental API. (into_future)

Which kind of future are we turning this into?

pub fn into_future(self) -> <F as IntoFuture>::Future[src]#

🔬 This is a nightly-only experimental API. (into_future)

Creates a future from a value.

impl<T, U> TryFrom<U> for T where U: Into<T>,[src]#

type Error = Infallible#

The type returned in the event of a conversion error.

pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>[src]#

Performs the conversion.

impl<F, T, E> TryFuture for F where F: Future<Output = Result<T, E>> + ?Sized,#

type Ok = T#

The type of successful values yielded by this future

type Error = E#

The type of failures yielded by this future

pub fn try_poll( self: Pin<&mutF>, cx: &mut Context<'_> ) -> Poll<<F as Future>::Output>#

Poll this TryFuture as if it were a Future. Read more

impl<Fut> TryFutureExt for Fut where Fut: TryFuture + ?Sized,#

fn flatten_sink<Item>(self) -> FlattenSink<Self, Self::Ok> where Self::Ok: Sink<Item>, <Self::Ok as Sink<Item>>::Error == Self::Error,#

Flattens the execution of this future when the successful result of this future is a [Sink]. Read more

fn map_ok<T, F>(self, f: F) -> MapOk<Self, F> where F: FnOnce(Self::Ok) -> T,#

Maps this future’s success value to a different value. Read more

fn map_ok_or_else<T, E, F>(self, e: E, f: F) -> MapOkOrElse<Self, F, E> where F: FnOnce(Self::Ok) -> T, E: FnOnce(Self::Error) -> T,#

Maps this future’s success value to a different value, and permits for error handling resulting in the same type. Read more

fn map_err<E, F>(self, f: F) -> MapErr<Self, F> where F: FnOnce(Self::Error) -> E,#

Maps this future’s error value to a different value. Read more

fn err_into<E>(self) -> ErrInto<Self, E> where Self::Error: Into<E>,#

Maps this future’s Error to a new error type using the Into trait. Read more

fn ok_into<U>(self) -> OkInto<Self, U> where Self::Ok: Into<U>,#

Maps this future’s Ok to a new type using the Into trait. Read more

fn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F> where F: FnOnce(Self::Ok) -> Fut, Fut: TryFuture<Error = Self::Error>,#

Executes another future after this one resolves successfully. The success value is passed to a closure to create this subsequent future. Read more

fn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F> where F: FnOnce(Self::Error) -> Fut, Fut: TryFuture<Ok = Self::Ok>,#

Executes another future if this one resolves to an error. The error value is passed to a closure to create this subsequent future. Read more

fn inspect_ok<F>(self, f: F) -> InspectOk<Self, F> where F: FnOnce(&Self::Ok),#

Do something with the success value of a future before passing it on. Read more

fn inspect_err<F>(self, f: F) -> InspectErr<Self, F> where F: FnOnce(&Self::Error),#

Do something with the error value of a future before passing it on. Read more

fn try_flatten(self) -> TryFlatten<Self, Self::Ok> where Self::Ok: TryFuture, <Self::Ok as TryFuture>::Error == Self::Error,#

Flatten the execution of this future when the successful result of this future is another future. Read more

fn try_flatten_stream(self) -> TryFlattenStream<Self> where Self::Ok: TryStream, <Self::Ok as TryStream>::Error == Self::Error,#

Flatten the execution of this future when the successful result of this future is a stream. Read more

fn unwrap_or_else<F>(self, f: F) -> UnwrapOrElse<Self, F> where F: FnOnce(Self::Error) -> Self::Ok,#

Unwraps this future’s output, producing a future with this future’s Ok type as its Output type. Read more

fn into_future(self) -> IntoFuture<Self>#

Wraps a [TryFuture] into a type that implements Future. Read more

fn try_poll_unpin( &mut self, cx: &mut Context<'_> ) -> Poll<Result<Self::Ok, Self::Error>> where Self: Unpin,#

A convenience method for calling [TryFuture::try_poll] on Unpin future types. Read more

impl<T, U> TryInto<U> for T where U: TryFrom<T>,[src]#

type Error = <U as TryFrom<T>>::Error#

The type returned in the event of a conversion error.

pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>[src]#

Performs the conversion.

impl<V, T> VZip<V> for T where V: MultiLane<T>,#

pub fn vzip(self) -> V#