## Waker

# Struct Waker

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    pub struct Waker { /* private fields */ }

Expand description

Waker allows cross-thread waking of `Poll`.

When created it will cause events with `readable` readiness and the provided `token` if `wake` is called, possibly from another thread.

## §Notes

`Waker` events are only guaranteed to be delivered while the `Waker` value is alive.

Only a single `Waker` can be active per `Poll`, if multiple threads need access to the `Waker` it can be shared via for example an `Arc`. What happens if multiple `Waker`s are registered with the same `Poll` is unspecified.

## §Implementation notes

On platforms that support kqueue this will use the `EVFILT_USER` event filter, see implementation notes of `Poll` to see what platforms support kqueue. On Linux it uses eventfd.

## §Examples

Wake a `Poll` instance from another thread.

    use std::thread;
    use std::time::Duration;
    use std::sync::Arc;

    use mio::{Events, Token, Poll, Waker};

    const WAKE_TOKEN: Token = Token(10);

    let mut poll = Poll::new()?;
    let mut events = Events::with_capacity(2);

    let waker = Arc::new(Waker::new(poll.registry(), WAKE_TOKEN)?);

    // We need to keep the Waker alive, so we'll create a clone for the
    // thread we create below.
    let waker1 = waker.clone();
    let handle = thread::spawn(move || {
        // Working hard, or hardly working?
        thread::sleep(Duration::from_millis(500));

        // Now we'll wake the queue on the other thread.
        waker1.wake().expect("unable to wake");
    });

    // On our current thread we'll poll for events, without a timeout.
    poll.poll(&mut events, None)?;

    // After about 500 milliseconds we should be awoken by the other thread and
    // get a single event.
    assert!(!events.is_empty());
    let waker_event = events.iter().next().unwrap();
    assert!(waker_event.is_readable());
    assert_eq!(waker_event.token(), WAKE_TOKEN);

## Implementations§

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### impl Waker

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#### pub fn new(registry: &Registry, token: Token) -> Result<Waker>

Create a new `Waker`.

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#### pub fn wake(&self) -> Result<()>

Wake up the `Poll` associated with this `Waker`.

## Trait Implementations§

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### impl Debug for Waker

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

Formats the value using the given formatter. Read more

## Auto Trait Implementations§

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### impl Freeze for Waker

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### impl RefUnwindSafe for Waker

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### impl Send for Waker

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### impl Sync for Waker

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### impl Unpin for Waker

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### impl UnwindSafe for Waker

## Blanket Implementations§

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

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.