Trait tokio_executor::TypedExecutor[−][src]

pub trait TypedExecutor<T> {
    fn spawn(&mut self, future: T) -> Result<(), SpawnError>;

    fn status(&self) -> Result<(), SpawnError> { ... }
}

A value that spawns futures of a specific type.

The trait is generic over T: the type of future that can be spawened. This is useful for implementing an executor that is only able to spawn a specific type of future.

The spawn function is used to submit the future to the executor. Once submitted, the executor takes ownership of the future and becomes responsible for driving the future to completion.

This trait is useful as a bound for applications and libraries in order to be generic over futures that are Send vs. !Send.

Examples

Consider a function that provides an API for draining a Stream in the background. To do this, a task must be spawned to perform the draining. As such, the function takes a stream and an executor on which the background task is spawned.

use tokio::executor::TypedExecutor;
use tokio::sync::oneshot;

use futures_core::{ready, Stream};
use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

async fn drain<T, E>(stream: T, executor: &mut E)
where
    T: Stream + Unpin,
    E: TypedExecutor<Drain<T>>
{
    let (tx, rx) = oneshot::channel();

    executor.spawn(Drain {
        stream,
        tx: Some(tx),
    }).unwrap();

    rx.await.unwrap()
}

// The background task
pub struct Drain<T> {
    stream: T,
    tx: Option<oneshot::Sender<()>>,
}

impl<T: Stream + Unpin> Future for Drain<T> {
    type Output = ();

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
        loop {
            let item = ready!(
                Pin::new(&mut self.stream).poll_next(cx)
            );

            if item.is_none() { break; }
        }

        let _ = self.tx.take().unwrap().send(()).map_err(|_| ());
        Poll::Ready(())
    }
}

By doing this, the drain fn can accept a stream that is !Send as long as the supplied executor is able to spawn !Send types.

Required methods

fn spawn(&mut self, future: T) -> Result<(), SpawnError>[src]

Spawns a future to run on this executor.

future is passed to the executor, which will begin running it. The executor takes ownership of the future and becomes responsible for driving the future to completion.

Panics

Implementations are encouraged to avoid panics. However, panics are permitted and the caller should check the implementation specific documentation for more details on possible panics.

Examples

use tokio_executor::TypedExecutor;

use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

fn example<T>(my_executor: &mut T)
where
    T: TypedExecutor<MyFuture>,
{
    my_executor.spawn(MyFuture).unwrap();
}

struct MyFuture;

impl Future for MyFuture {
    type Output = ();

    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<()> {
        println!("running on the executor");
        Poll::Ready(())
    }
}
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Provided methods

fn status(&self) -> Result<(), SpawnError>[src]

Provides a best effort hint to whether or not spawn will succeed.

This function may return both false positives and false negatives. If status returns Ok, then a call to spawn will probably succeed, but may fail. If status returns Err, a call to spawn will probably fail, but may succeed.

This allows a caller to avoid creating the task if the call to spawn has a high likelihood of failing.

Panics

This function must not panic. Implementers must ensure that panics do not happen.

Examples

use tokio_executor::TypedExecutor;

use std::future::Future;
use std::pin::Pin;
use std::task::{Context, Poll};

fn example<T>(my_executor: &mut T)
where
    T: TypedExecutor<MyFuture>,
{
    if my_executor.status().is_ok() {
        my_executor.spawn(MyFuture).unwrap();
    } else {
        println!("the executor is not in a good state");
    }
}

struct MyFuture;

impl Future for MyFuture {
    type Output = ();

    fn poll(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<()> {
        println!("running on the executor");
        Poll::Ready(())
    }
}
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Implementations on Foreign Types

impl<E, T> TypedExecutor<T> for Box<E> where
    E: TypedExecutor<T>, [src]

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Implementors

impl<T> TypedExecutor<T> for DefaultExecutor where
    T: Future<Output = ()> + Send + 'static, [src]

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