Struct actix_web::rt::task::JoinHandle
[−]pub struct JoinHandle<T> { /* private fields */ }
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.
Cancel safety
The &mut JoinHandle<T>
type is cancel safe. If it is used as the event
in a tokio::select!
statement and some other branch completes first,
then it is guaranteed that the output of the task is not lost.
If a JoinHandle
is dropped, then the task continues running in the
background and its return value is lost.
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>
impl<T> JoinHandle<T>
pub fn abort(&self)
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 fail with a cancelled JoinError
.
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());
}
}
pub fn is_finished(&self) -> bool
pub fn is_finished(&self) -> bool
Checks if the task associated with this JoinHandle
has finished.
Please note that this method can return false
even if abort
has been
called on the task. This is because the cancellation process may take
some time, and this method does not return true
until it has
completed.
use tokio::time;
let handle1 = tokio::spawn(async {
// do some stuff here
});
let handle2 = tokio::spawn(async {
// do some other stuff here
time::sleep(time::Duration::from_secs(10)).await;
});
// Wait for the task to finish
handle2.abort();
time::sleep(time::Duration::from_secs(1)).await;
assert!(handle1.is_finished());
assert!(handle2.is_finished());
Trait Implementations
impl<T> Debug for JoinHandle<T>where
T: Debug,
impl<T> Debug for JoinHandle<T>where
T: Debug,
impl<T> Drop for JoinHandle<T>
impl<T> Drop for JoinHandle<T>
impl<T> Future for JoinHandle<T>
impl<T> Future for JoinHandle<T>
fn poll(
self: Pin<&mut JoinHandle<T>>,
cx: &mut Context<'_>
) -> Poll<<JoinHandle<T> as Future>::Output>
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> RefUnwindSafe for JoinHandle<T>
impl<T> Send for JoinHandle<T>where
T: Send,
impl<T> Sync for JoinHandle<T>where
T: Send,
impl<T> Unpin for JoinHandle<T>
impl<T> UnwindSafe for JoinHandle<T>
Blanket Implementations
sourceimpl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
const: unstable · sourcefn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
sourceimpl<T> FutureExt for Twhere
T: Future + ?Sized,
impl<T> FutureExt for Twhere
T: Future + ?Sized,
sourcefn map<U, F>(self, f: F) -> Map<Self, F>where
F: FnOnce(Self::Output) -> U,
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
sourcefn map_into<U>(self) -> MapInto<Self, U>where
Self::Output: Into<U>,
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
sourcefn then<Fut, F>(self, f: F) -> Then<Self, Fut, F>where
F: FnOnce(Self::Output) -> Fut,
Fut: Future,
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
sourcefn left_future<B>(self) -> Either<Self, B>where
B: Future<Output = Self::Output>,
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
sourcefn right_future<A>(self) -> Either<A, Self>where
A: Future<Output = Self::Output>,
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
sourcefn into_stream(self) -> IntoStream<Self>
fn into_stream(self) -> IntoStream<Self>
Convert this future into a single element stream. Read more
sourcefn flatten(self) -> Flatten<Self>where
Self::Output: Future,
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
sourcefn flatten_stream(self) -> FlattenStream<Self>where
Self::Output: Stream,
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
sourcefn fuse(self) -> Fuse<Self>
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
sourcefn inspect<F>(self, f: F) -> Inspect<Self, F>where
F: FnOnce(&Self::Output),
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
sourcefn boxed<'a>(
self
) -> Pin<Box<dyn Future<Output = Self::Output> + Send + 'a, Global>>where
Self: 'a + Send,
fn boxed<'a>(
self
) -> Pin<Box<dyn Future<Output = Self::Output> + Send + 'a, Global>>where
Self: 'a + Send,
Wrap the future in a Box, pinning it. Read more
sourcefn boxed_local<'a>(
self
) -> Pin<Box<dyn Future<Output = Self::Output> + 'a, Global>>where
Self: 'a,
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
sourcefn unit_error(self) -> UnitError<Self>
fn unit_error(self) -> UnitError<Self>
Turns a Future<Output = T>
into a
TryFuture<Ok = T, Error = ()
>. Read more
sourcefn never_error(self) -> NeverError<Self>
fn never_error(self) -> NeverError<Self>
Turns a Future<Output = T>
into a
TryFuture<Ok = T, Error = Never
>. Read more
sourcefn poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Self::Output>where
Self: Unpin,
fn poll_unpin(&mut self, cx: &mut Context<'_>) -> Poll<Self::Output>where
Self: Unpin,
A convenience for calling Future::poll
on Unpin
future types.
sourcefn now_or_never(self) -> Option<Self::Output>
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
sourceimpl<T> Instrument for T
impl<T> Instrument for T
sourcefn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
sourcefn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
sourceimpl<F> IntoFuture for Fwhere
F: Future,
impl<F> IntoFuture for Fwhere
F: Future,
type IntoFuture = F
type IntoFuture = F
Which kind of future are we turning this into?
sourcefn into_future(self) -> <F as IntoFuture>::IntoFuture
fn into_future(self) -> <F as IntoFuture>::IntoFuture
Creates a future from a value. Read more
sourceimpl<Fut> TryFutureExt for Futwhere
Fut: TryFuture + ?Sized,
impl<Fut> TryFutureExt for Futwhere
Fut: TryFuture + ?Sized,
sourcefn map_ok<T, F>(self, f: F) -> MapOk<Self, F>where
F: FnOnce(Self::Ok) -> T,
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
sourcefn 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,
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
sourcefn map_err<E, F>(self, f: F) -> MapErr<Self, F>where
F: FnOnce(Self::Error) -> E,
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
sourcefn and_then<Fut, F>(self, f: F) -> AndThen<Self, Fut, F>where
F: FnOnce(Self::Ok) -> Fut,
Fut: TryFuture<Error = Self::Error>,
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
sourcefn or_else<Fut, F>(self, f: F) -> OrElse<Self, Fut, F>where
F: FnOnce(Self::Error) -> Fut,
Fut: TryFuture<Ok = Self::Ok>,
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
sourcefn inspect_ok<F>(self, f: F) -> InspectOk<Self, F>where
F: FnOnce(&Self::Ok),
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
sourcefn inspect_err<F>(self, f: F) -> InspectErr<Self, F>where
F: FnOnce(&Self::Error),
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
sourcefn try_flatten(self) -> TryFlatten<Self, Self::Ok>where
Self::Ok: TryFuture,
<Self::Ok as TryFuture>::Error == Self::Error,
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
sourcefn try_flatten_stream(self) -> TryFlattenStream<Self>where
Self::Ok: TryStream,
<Self::Ok as TryStream>::Error == Self::Error,
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
sourcefn unwrap_or_else<F>(self, f: F) -> UnwrapOrElse<Self, F>where
F: FnOnce(Self::Error) -> Self::Ok,
fn unwrap_or_else<F>(self, f: F) -> UnwrapOrElse<Self, F>where
F: FnOnce(Self::Error) -> Self::Ok,
sourcefn into_future(self) -> IntoFuture<Self>
fn into_future(self) -> IntoFuture<Self>
impl<V, T> VZip<V> for Twhere
V: MultiLane<T>,
impl<V, T> VZip<V> for Twhere
V: MultiLane<T>,
fn vzip(self) -> V
sourceimpl<T> WithSubscriber for T
impl<T> WithSubscriber for T
sourcefn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>where
S: Into<Dispatch>,
fn with_subscriber<S>(self, subscriber: S) -> WithDispatch<Self>where
S: Into<Dispatch>,
Attaches the provided Subscriber
to this type, returning a
WithDispatch
wrapper. Read more
sourcefn with_current_subscriber(self) -> WithDispatch<Self>
fn with_current_subscriber(self) -> WithDispatch<Self>
Attaches the current default Subscriber
to this type, returning a
WithDispatch
wrapper. Read more