Struct tokio::time::DelayQueue [−][src]
A queue of delayed elements.
Once an element is inserted into the DelayQueue
, it is yielded once the
specified deadline has been reached.
Usage
Elements are inserted into DelayQueue
using the insert
or
insert_at
methods. A deadline is provided with the item and a Key
is
returned. The key is used to remove the entry or to change the deadline at
which it should be yielded back.
Once delays have been configured, the DelayQueue
is used via its
Stream
implementation. poll_expired
is called. If an entry has reached its
deadline, it is returned. If not, Poll::Pending
indicating that the
current task will be notified once the deadline has been reached.
Stream
implementation
Items are retrieved from the queue via DelayQueue::poll_expired
. If no delays have
expired, no items are returned. In this case, NotReady
is returned and the
current task is registered to be notified once the next item’s delay has
expired.
If no items are in the queue, i.e. is_empty()
returns true
, then poll
returns Ready(None)
. This indicates that the stream has reached an end.
However, if a new item is inserted after, poll
will once again start
returning items or `NotReady.
Items are returned ordered by their expirations. Items that are configured to expire first will be returned first. There are no ordering guarantees for items configured to expire the same instant. Also note that delays are rounded to the closest millisecond.
Implementation
The DelayQueue
is backed by a separate instance of the same timer wheel used internally by
Tokio’s standalone timer utilities such as delay_for
. Because of this, it offers the same
performance and scalability benefits.
State associated with each entry is stored in a slab
. This amortizes the cost of allocation,
and allows reuse of the memory allocated for expired entires.
Capacity can be checked using capacity
and allocated preemptively by using
the reserve
method.
Usage
Using DelayQueue
to manage cache entries.
use tokio::time::{delay_queue, DelayQueue, Error}; use futures::ready; use std::collections::HashMap; use std::task::{Context, Poll}; use std::time::Duration; struct Cache { entries: HashMap<CacheKey, (Value, delay_queue::Key)>, expirations: DelayQueue<CacheKey>, } const TTL_SECS: u64 = 30; impl Cache { fn insert(&mut self, key: CacheKey, value: Value) { let delay = self.expirations .insert(key.clone(), Duration::from_secs(TTL_SECS)); self.entries.insert(key, (value, delay)); } fn get(&self, key: &CacheKey) -> Option<&Value> { self.entries.get(key) .map(|&(ref v, _)| v) } fn remove(&mut self, key: &CacheKey) { if let Some((_, cache_key)) = self.entries.remove(key) { self.expirations.remove(&cache_key); } } fn poll_purge(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Error>> { while let Some(res) = ready!(self.expirations.poll_expired(cx)) { let entry = res?; self.entries.remove(entry.get_ref()); } Poll::Ready(Ok(())) } }
Implementations
impl<T> DelayQueue<T>
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pub fn new() -> DelayQueue<T>
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Creates a new, empty, DelayQueue
The queue will not allocate storage until items are inserted into it.
Examples
let delay_queue: DelayQueue<u32> = DelayQueue::new();
pub fn with_capacity(capacity: usize) -> DelayQueue<T>
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Creates a new, empty, DelayQueue
with the specified capacity.
The queue will be able to hold at least capacity
elements without
reallocating. If capacity
is 0, the queue will not allocate for
storage.
Examples
let mut delay_queue = DelayQueue::with_capacity(10); // These insertions are done without further allocation for i in 0..10 { delay_queue.insert(i, Duration::from_secs(i)); } // This will make the queue allocate additional storage delay_queue.insert(11, Duration::from_secs(11));
pub fn insert_at(&mut self, value: T, when: Instant) -> Key
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Inserts value
into the queue set to expire at a specific instant in
time.
This function is identical to insert
, but takes an Instant
instead
of a Duration
.
value
is stored in the queue until when
is reached. At which point,
value
will be returned from poll_expired
. If when
has already been
reached, then value
is immediately made available to poll.
The return value represents the insertion and is used at an argument to
remove
and reset
. Note that Key
is token and is reused once
value
is removed from the queue either by calling poll_expired
after
when
is reached or by calling remove
. At this point, the caller
must take care to not use the returned Key
again as it may reference
a different item in the queue.
See type level documentation for more details.
Panics
This function panics if when
is too far in the future.
Examples
Basic usage
use tokio::time::{DelayQueue, Duration, Instant}; let mut delay_queue = DelayQueue::new(); let key = delay_queue.insert_at( "foo", Instant::now() + Duration::from_secs(5)); // Remove the entry let item = delay_queue.remove(&key); assert_eq!(*item.get_ref(), "foo");
pub fn poll_expired(
&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Expired<T>, Error>>>
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&mut self,
cx: &mut Context<'_>
) -> Poll<Option<Result<Expired<T>, Error>>>
Attempts to pull out the next value of the delay queue, registering the current task for wakeup if the value is not yet available, and returning None if the queue is exhausted.
pub fn insert(&mut self, value: T, timeout: Duration) -> Key
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Inserts value
into the queue set to expire after the requested duration
elapses.
This function is identical to insert_at
, but takes a Duration
instead of an Instant
.
value
is stored in the queue until when
is reached. At which point,
value
will be returned from poll_expired
. If when
has already been
reached, then value
is immediately made available to poll.
The return value represents the insertion and is used at an argument to
remove
and reset
. Note that Key
is token and is reused once
value
is removed from the queue either by calling poll_expired
after
when
is reached or by calling remove
. At this point, the caller
must take care to not use the returned Key
again as it may reference
a different item in the queue.
See type level documentation for more details.
Panics
This function panics if timeout
is greater than the maximum supported
duration.
Examples
Basic usage
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue = DelayQueue::new(); let key = delay_queue.insert("foo", Duration::from_secs(5)); // Remove the entry let item = delay_queue.remove(&key); assert_eq!(*item.get_ref(), "foo");
pub fn remove(&mut self, key: &Key) -> Expired<T>
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Removes the item associated with key
from the queue.
There must be an item associated with key
. The function returns the
removed item as well as the Instant
at which it will the delay will
have expired.
Panics
The function panics if key
is not contained by the queue.
Examples
Basic usage
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue = DelayQueue::new(); let key = delay_queue.insert("foo", Duration::from_secs(5)); // Remove the entry let item = delay_queue.remove(&key); assert_eq!(*item.get_ref(), "foo");
pub fn reset_at(&mut self, key: &Key, when: Instant)
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Sets the delay of the item associated with key
to expire at when
.
This function is identical to reset
but takes an Instant
instead of
a Duration
.
The item remains in the queue but the delay is set to expire at when
.
If when
is in the past, then the item is immediately made available to
the caller.
Panics
This function panics if when
is too far in the future or if key
is
not contained by the queue.
Examples
Basic usage
use tokio::time::{DelayQueue, Duration, Instant}; let mut delay_queue = DelayQueue::new(); let key = delay_queue.insert("foo", Duration::from_secs(5)); // "foo" is scheduled to be returned in 5 seconds delay_queue.reset_at(&key, Instant::now() + Duration::from_secs(10)); // "foo"is now scheduled to be returned in 10 seconds
pub fn reset(&mut self, key: &Key, timeout: Duration)
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Sets the delay of the item associated with key
to expire after
timeout
.
This function is identical to reset_at
but takes a Duration
instead
of an Instant
.
The item remains in the queue but the delay is set to expire after
timeout
. If timeout
is zero, then the item is immediately made
available to the caller.
Panics
This function panics if timeout
is greater than the maximum supported
duration or if key
is not contained by the queue.
Examples
Basic usage
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue = DelayQueue::new(); let key = delay_queue.insert("foo", Duration::from_secs(5)); // "foo" is scheduled to be returned in 5 seconds delay_queue.reset(&key, Duration::from_secs(10)); // "foo"is now scheduled to be returned in 10 seconds
pub fn clear(&mut self)
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Clears the queue, removing all items.
After calling clear
, poll_expired
will return Ok(Ready(None))
.
Note that this method has no effect on the allocated capacity.
Examples
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue = DelayQueue::new(); delay_queue.insert("foo", Duration::from_secs(5)); assert!(!delay_queue.is_empty()); delay_queue.clear(); assert!(delay_queue.is_empty());
pub fn capacity(&self) -> usize
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Returns the number of elements the queue can hold without reallocating.
Examples
use tokio::time::DelayQueue; let delay_queue: DelayQueue<i32> = DelayQueue::with_capacity(10); assert_eq!(delay_queue.capacity(), 10);
pub fn len(&self) -> usize
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Returns the number of elements currently in the queue.
Examples
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue: DelayQueue<i32> = DelayQueue::with_capacity(10); assert_eq!(delay_queue.len(), 0); delay_queue.insert(3, Duration::from_secs(5)); assert_eq!(delay_queue.len(), 1);
pub fn reserve(&mut self, additional: usize)
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Reserves capacity for at least additional
more items to be queued
without allocating.
reserve
does nothing if the queue already has sufficient capacity for
additional
more values. If more capacity is required, a new segment of
memory will be allocated and all existing values will be copied into it.
As such, if the queue is already very large, a call to reserve
can end
up being expensive.
The queue may reserve more than additional
extra space in order to
avoid frequent reallocations.
Panics
Panics if the new capacity exceeds the maximum number of entries the queue can contain.
Examples
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue = DelayQueue::new(); delay_queue.insert("hello", Duration::from_secs(10)); delay_queue.reserve(10); assert!(delay_queue.capacity() >= 11);
pub fn is_empty(&self) -> bool
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Returns true
if there are no items in the queue.
Note that this function returns false
even if all items have not yet
expired and a call to poll
will return NotReady
.
Examples
use tokio::time::DelayQueue; use std::time::Duration; let mut delay_queue = DelayQueue::new(); assert!(delay_queue.is_empty()); delay_queue.insert("hello", Duration::from_secs(5)); assert!(!delay_queue.is_empty());
Trait Implementations
impl<T: Debug> Debug for DelayQueue<T>
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impl<T> Default for DelayQueue<T>
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fn default() -> DelayQueue<T>
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impl<T> Stream for DelayQueue<T>
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type Item = Result<Expired<T>, Error>
Values yielded by the stream.
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>>
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self: Pin<&mut Self>,
cx: &mut Context<'_>
) -> Poll<Option<Self::Item>>
pub fn size_hint(&self) -> (usize, Option<usize>)
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impl<T> Unpin for DelayQueue<T>
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Auto Trait Implementations
impl<T> !RefUnwindSafe for DelayQueue<T>
impl<T> Send for DelayQueue<T> where
T: Send,
T: Send,
impl<T> Sync for DelayQueue<T> where
T: Sync,
T: Sync,
impl<T> !UnwindSafe for DelayQueue<T>
Blanket Implementations
impl<T> Any for T where
T: 'static + ?Sized,
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T: 'static + ?Sized,
impl<T> Borrow<T> for T where
T: ?Sized,
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T: ?Sized,
impl<T> BorrowMut<T> for T where
T: ?Sized,
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T: ?Sized,
pub fn borrow_mut(&mut self) -> &mut Tⓘ
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impl<T> From<T> for T
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impl<T, U> Into<U> for T where
U: From<T>,
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U: From<T>,
impl<St> StreamExt for St where
St: Stream + ?Sized,
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St: Stream + ?Sized,
fn next(&mut self) -> Next<'_, Self> where
Self: Unpin,
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Self: Unpin,
fn try_next<T, E>(&mut self) -> TryNext<'_, Self> where
Self: Stream<Item = Result<T, E>> + Unpin,
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Self: Stream<Item = Result<T, E>> + Unpin,
fn map<T, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> T,
Self: Sized,
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F: FnMut(Self::Item) -> T,
Self: Sized,
fn merge<U>(self, other: U) -> Merge<Self, U> where
U: Stream<Item = Self::Item>,
Self: Sized,
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U: Stream<Item = Self::Item>,
Self: Sized,
fn filter<F>(self, f: F) -> Filter<Self, F> where
F: FnMut(&Self::Item) -> bool,
Self: Sized,
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F: FnMut(&Self::Item) -> bool,
Self: Sized,
fn filter_map<T, F>(self, f: F) -> FilterMap<Self, F> where
F: FnMut(Self::Item) -> Option<T>,
Self: Sized,
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F: FnMut(Self::Item) -> Option<T>,
Self: Sized,
fn fuse(self) -> Fuse<Self> where
Self: Sized,
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Self: Sized,
fn take(self, n: usize) -> Take<Self> where
Self: Sized,
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Self: Sized,
fn take_while<F>(self, f: F) -> TakeWhile<Self, F> where
F: FnMut(&Self::Item) -> bool,
Self: Sized,
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F: FnMut(&Self::Item) -> bool,
Self: Sized,
fn skip(self, n: usize) -> Skip<Self> where
Self: Sized,
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Self: Sized,
fn skip_while<F>(self, f: F) -> SkipWhile<Self, F> where
F: FnMut(&Self::Item) -> bool,
Self: Sized,
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F: FnMut(&Self::Item) -> bool,
Self: Sized,
fn all<F>(&mut self, f: F) -> AllFuture<'_, Self, F> where
Self: Unpin,
F: FnMut(Self::Item) -> bool,
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Self: Unpin,
F: FnMut(Self::Item) -> bool,
fn any<F>(&mut self, f: F) -> AnyFuture<'_, Self, F> where
Self: Unpin,
F: FnMut(Self::Item) -> bool,
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Self: Unpin,
F: FnMut(Self::Item) -> bool,
fn chain<U>(self, other: U) -> Chain<Self, U> where
U: Stream<Item = Self::Item>,
Self: Sized,
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U: Stream<Item = Self::Item>,
Self: Sized,
fn fold<B, F>(self, init: B, f: F) -> FoldFuture<Self, B, F> where
Self: Sized,
F: FnMut(B, Self::Item) -> B,
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Self: Sized,
F: FnMut(B, Self::Item) -> B,
fn collect<T>(self) -> Collect<Self, T> where
T: FromStream<Self::Item>,
Self: Sized,
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T: FromStream<Self::Item>,
Self: Sized,
fn timeout(self, duration: Duration) -> Timeout<Self> where
Self: Sized,
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Self: Sized,
impl<T, U> TryFrom<U> for T where
U: Into<T>,
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U: Into<T>,
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>
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impl<T, U> TryInto<U> for T where
U: TryFrom<T>,
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U: TryFrom<T>,
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>
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impl<S, T, E> TryStream for S where
S: Stream<Item = Result<T, E>> + ?Sized,
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S: Stream<Item = Result<T, E>> + ?Sized,