[−][src]Struct futures_util::task::AtomicWaker
A synchronization primitive for task wakeup.
Sometimes the task interested in a given event will change over time.
An AtomicWaker
can coordinate concurrent notifications with the consumer
potentially "updating" the underlying task to wake up. This is useful in
scenarios where a computation completes in another thread and wants to
notify the consumer, but the consumer is in the process of being migrated to
a new logical task.
Consumers should call register
before checking the result of a computation
and producers should call wake
after producing the computation (this
differs from the usual thread::park
pattern). It is also permitted for
wake
to be called before register
. This results in a no-op.
A single AtomicWaker
may be reused for any number of calls to register
or
wake
.
AtomicWaker
does not provide any memory ordering guarantees, as such the
user should use caution and use other synchronization primitives to guard
the result of the underlying computation.
Methods
impl AtomicWaker
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impl AtomicWaker
pub fn new() -> AtomicWaker
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pub fn new() -> AtomicWaker
Create an AtomicWaker
.
pub fn register(&self, lw: &LocalWaker)
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pub fn register(&self, lw: &LocalWaker)
Registers the waker to be notified on calls to wake
.
The new task will take place of any previous tasks that were registered
by previous calls to register
. Any calls to wake
that happen after
a call to register
(as defined by the memory ordering rules), will
notify the register
caller's task and deregister the waker from future
notifications. Because of this, callers should ensure register
gets
invoked with a new Waker
each time they require a wakeup.
It is safe to call register
with multiple other threads concurrently
calling wake
. This will result in the register
caller's current
task being notified once.
This function is safe to call concurrently, but this is generally a bad
idea. Concurrent calls to register
will attempt to register different
tasks to be notified. One of the callers will win and have its task set,
but there is no guarantee as to which caller will succeed.
Examples
Here is how register
is used when implementing a flag.
#![feature(pin, arbitrary_self_types, futures_api)] use futures::future::Future; use futures::task::{LocalWaker, Poll, AtomicWaker}; use std::sync::atomic::AtomicBool; use std::sync::atomic::Ordering::SeqCst; use std::pin::Pin; struct Flag { waker: AtomicWaker, set: AtomicBool, } impl Future for Flag { type Output = (); fn poll(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<()> { // Register **before** checking `set` to avoid a race condition // that would result in lost notifications. self.waker.register(lw); if self.set.load(SeqCst) { Poll::Ready(()) } else { Poll::Pending } } }
pub fn wake(&self)
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pub fn wake(&self)
Calls wake
on the last Waker
passed to register
.
If register
has not been called yet, then this does nothing.
Trait Implementations
impl Sync for AtomicWaker
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impl Sync for AtomicWaker
impl Default for AtomicWaker
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impl Default for AtomicWaker
impl Send for AtomicWaker
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impl Send for AtomicWaker
impl Debug for AtomicWaker
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impl Debug for AtomicWaker
Blanket Implementations
impl<T, U> Into for T where
U: From<T>,
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impl<T, U> Into for T where
U: From<T>,
impl<T> From for T
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impl<T> From for T
impl<T, U> TryFrom for T where
T: From<U>,
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impl<T, U> TryFrom for T where
T: From<U>,
type Error = !
try_from
)The type returned in the event of a conversion error.
fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
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fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>
try_from
)Performs the conversion.
impl<T> Borrow for T where
T: ?Sized,
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impl<T> Borrow for T where
T: ?Sized,
ⓘImportant traits for &'_ mut Ifn borrow(&self) -> &T
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fn borrow(&self) -> &T
Immutably borrows from an owned value. Read more
impl<T> Any for T where
T: 'static + ?Sized,
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impl<T> Any for T where
T: 'static + ?Sized,
fn get_type_id(&self) -> TypeId
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fn get_type_id(&self) -> TypeId
🔬 This is a nightly-only experimental API. (get_type_id
)
this method will likely be replaced by an associated static
Gets the TypeId
of self
. Read more
impl<T> BorrowMut for T where
T: ?Sized,
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impl<T> BorrowMut for T where
T: ?Sized,
ⓘImportant traits for &'_ mut Ifn borrow_mut(&mut self) -> &mut T
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fn borrow_mut(&mut self) -> &mut T
Mutably borrows from an owned value. Read more
impl<T, U> TryInto for T where
U: TryFrom<T>,
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impl<T, U> TryInto for T where
U: TryFrom<T>,