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//! A queue of delayed elements. //! //! See [`DelayQueue`] for more details. //! //! [`DelayQueue`]: struct.DelayQueue.html use clock::now; use timer::Handle; use wheel::{self, Wheel}; use {Delay, Error}; use futures::{Future, Poll, Stream}; use slab::Slab; use std::cmp; use std::marker::PhantomData; use std::time::{Duration, Instant}; /// 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`] is called. If an entry has reached its /// deadline, it is returned. If not, `Async::NotReady` indicating that the /// current task will be notified once the deadline has been reached. /// /// # `Stream` implementation /// /// Items are retrieved from the queue via [`Stream::poll`]. 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 the same hashed timing wheel implementation as /// [`Timer`] as such, it offers the same performance benefits. See [`Timer`] /// for further implementation notes. /// /// State associated with each entry is stored in a [`slab`]. This allows /// amortizing the cost of allocation. Space created for expired entries is /// reused when inserting new entries. /// /// Capacity can be checked using [`capacity`] and allocated preemptively by using /// the [`reserve`] method. /// /// # Usage /// /// Using `DelayQueue` to manage cache entries. /// /// ```rust /// #[macro_use] /// extern crate futures; /// extern crate tokio; /// # type CacheKey = String; /// # type Value = String; /// use tokio::timer::{delay_queue, DelayQueue, Error}; /// use futures::{Async, Poll, Stream}; /// use std::collections::HashMap; /// 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) -> Poll<(), Error> { /// while let Some(entry) = try_ready!(self.expirations.poll()) { /// self.entries.remove(entry.get_ref()); /// } /// /// Ok(Async::Ready(())) /// } /// } /// # fn main() {} /// ``` /// /// [`insert`]: #method.insert /// [`insert_at`]: #method.insert_at /// [`Key`]: struct.Key.html /// [`Stream`]: https://docs.rs/futures/0.1/futures/stream/trait.Stream.html /// [`poll`]: #method.poll /// [`Stream::poll`]: #method.poll /// [`Timer`]: ../struct.Timer.html /// [`slab`]: https://docs.rs/slab /// [`capacity`]: #method.capacity /// [`reserve`]: #method.reserve #[derive(Debug)] pub struct DelayQueue<T> { /// Handle to the timer driving the `DelayQueue` handle: Handle, /// Stores data associated with entries slab: Slab<Data<T>>, /// Lookup structure tracking all delays in the queue wheel: Wheel<Stack<T>>, /// Delays that were inserted when already expired. These cannot be stored /// in the wheel expired: Stack<T>, /// Delay expiring when the *first* item in the queue expires delay: Option<Delay>, /// Wheel polling state poll: wheel::Poll, /// Instant at which the timer starts start: Instant, } /// An entry in `DelayQueue` that has expired and removed. /// /// Values are returned by [`DelayQueue::poll`]. /// /// [`DelayQueue::poll`]: struct.DelayQueue.html#method.poll #[derive(Debug)] pub struct Expired<T> { /// The data stored in the queue data: T, /// The expiration time deadline: Instant, /// The key associated with the entry key: Key, } /// Token to a value stored in a `DelayQueue`. /// /// Instances of `Key` are returned by [`DelayQueue::insert`]. See [`DelayQueue`] /// documentation for more details. /// /// [`DelayQueue`]: struct.DelayQueue.html /// [`DelayQueue::insert`]: struct.DelayQueue.html#method.insert #[derive(Debug, Clone)] pub struct Key { index: usize, } #[derive(Debug)] struct Stack<T> { /// Head of the stack head: Option<usize>, _p: PhantomData<T>, } #[derive(Debug)] struct Data<T> { /// The data being stored in the queue and will be returned at the requested /// instant. inner: T, /// The instant at which the item is returned. when: u64, /// Set to true when stored in the `expired` queue expired: bool, /// Next entry in the stack next: Option<usize>, /// Previous entry in the stack prev: Option<usize>, } /// Maximum number of entries the queue can handle const MAX_ENTRIES: usize = (1 << 30) - 1; impl<T> DelayQueue<T> { /// Create a new, empty, `DelayQueue` /// /// The queue will not allocate storage until items are inserted into it. /// /// # Examples /// /// ```rust /// # use tokio_timer::DelayQueue; /// let delay_queue: DelayQueue<u32> = DelayQueue::new(); /// ``` pub fn new() -> DelayQueue<T> { DelayQueue::with_capacity(0) } /// Create a new, empty, `DelayQueue` backed by the specified timer. /// /// The queue will not allocate storage until items are inserted into it. /// /// # Examples /// /// ```rust,no_run /// # use tokio_timer::DelayQueue; /// use tokio_timer::timer::Handle; /// /// let handle = Handle::default(); /// let delay_queue: DelayQueue<u32> = DelayQueue::with_capacity_and_handle(0, &handle); /// ``` pub fn with_capacity_and_handle(capacity: usize, handle: &Handle) -> DelayQueue<T> { DelayQueue { handle: handle.clone(), wheel: Wheel::new(), slab: Slab::with_capacity(capacity), expired: Stack::default(), delay: None, poll: wheel::Poll::new(0), start: now(), } } /// Create 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 /// /// ```rust /// # use tokio_timer::DelayQueue; /// # use std::time::Duration; /// 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 with_capacity(capacity: usize) -> DelayQueue<T> { DelayQueue::with_capacity_and_handle(capacity, &Handle::default()) } /// Insert `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`]. 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`] 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 /// /// ```rust /// # extern crate tokio; /// use tokio::timer::DelayQueue; /// use std::time::{Instant, Duration}; /// /// # fn main() { /// 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"); /// # } /// ``` /// /// [`poll`]: #method.poll /// [`remove`]: #method.remove /// [`reset`]: #method.reset /// [`Key`]: struct.Key.html /// [type]: # pub fn insert_at(&mut self, value: T, when: Instant) -> Key { assert!(self.slab.len() < MAX_ENTRIES, "max entries exceeded"); // Normalize the deadline. Values cannot be set to expire in the past. let when = self.normalize_deadline(when); // Insert the value in the store let key = self.slab.insert(Data { inner: value, when, expired: false, next: None, prev: None, }); self.insert_idx(when, key); // Set a new delay if the current's deadline is later than the one of the new item let should_set_delay = if let Some(ref delay) = self.delay { let current_exp = self.normalize_deadline(delay.deadline()); current_exp > when } else { true }; if should_set_delay { self.delay = Some(self.handle.delay(self.start + Duration::from_millis(when))); } Key::new(key) } /// Insert `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`]. 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`] 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 /// /// ```rust /// # extern crate tokio; /// use tokio::timer::DelayQueue; /// use std::time::Duration; /// /// # fn main() { /// 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"); /// # } /// ``` /// /// [`poll`]: #method.poll /// [`remove`]: #method.remove /// [`reset`]: #method.reset /// [`Key`]: struct.Key.html /// [type]: # pub fn insert(&mut self, value: T, timeout: Duration) -> Key { self.insert_at(value, now() + timeout) } fn insert_idx(&mut self, when: u64, key: usize) { use self::wheel::{InsertError, Stack}; // Register the deadline with the timer wheel match self.wheel.insert(when, key, &mut self.slab) { Ok(_) => {} Err((_, InsertError::Elapsed)) => { self.slab[key].expired = true; // The delay is already expired, store it in the expired queue self.expired.push(key, &mut self.slab); } Err((_, err)) => panic!("invalid deadline; err={:?}", err), } } /// Remove 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 /// /// ```rust /// # extern crate tokio; /// use tokio::timer::DelayQueue; /// use std::time::Duration; /// /// # fn main() { /// 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> { use wheel::Stack; // Special case the `expired` queue if self.slab[key.index].expired { self.expired.remove(&key.index, &mut self.slab); } else { self.wheel.remove(&key.index, &mut self.slab); } let data = self.slab.remove(key.index); Expired { key: Key::new(key.index), data: data.inner, deadline: self.start + Duration::from_millis(data.when), } } /// 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 /// /// ```rust /// # extern crate tokio; /// use tokio::timer::DelayQueue; /// use std::time::{Duration, Instant}; /// /// # fn main() { /// 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_at(&mut self, key: &Key, when: Instant) { self.wheel.remove(&key.index, &mut self.slab); // Normalize the deadline. Values cannot be set to expire in the past. let when = self.normalize_deadline(when); self.slab[key.index].when = when; self.insert_idx(when, key.index); let next_deadline = self.next_deadline(); if let (Some(ref mut delay), Some(deadline)) = (&mut self.delay, next_deadline) { delay.reset(deadline); } } /// Returns the next time poll as determined by the wheel fn next_deadline(&mut self) -> Option<Instant> { self.wheel .poll_at() .map(|poll_at| self.start + Duration::from_millis(poll_at)) } /// 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 /// /// ```rust /// # extern crate tokio; /// use tokio::timer::DelayQueue; /// use std::time::Duration; /// /// # fn main() { /// 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 reset(&mut self, key: &Key, timeout: Duration) { self.reset_at(key, now() + timeout); } /// Clears the queue, removing all items. /// /// After calling `clear`, [`poll`] will return `Ok(Ready(None))`. /// /// Note that this method has no effect on the allocated capacity. /// /// [`poll`]: #method.poll /// /// # Examples /// /// ```rust /// # extern crate tokio; /// use tokio::timer::DelayQueue; /// use std::time::Duration; /// /// # fn main() { /// 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 clear(&mut self) { self.slab.clear(); self.expired = Stack::default(); self.wheel = Wheel::new(); self.delay = None; } /// Returns the number of elements the queue can hold without reallocating. /// /// # Examples /// /// ```rust /// # use tokio_timer::DelayQueue; /// let delay_queue: DelayQueue<i32> = DelayQueue::with_capacity(10); /// assert_eq!(delay_queue.capacity(), 10); /// ``` pub fn capacity(&self) -> usize { self.slab.capacity() } /// Reserve 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_timer::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 reserve(&mut self, additional: usize) { self.slab.reserve(additional); } /// 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_timer::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()); /// ``` pub fn is_empty(&self) -> bool { self.slab.is_empty() } /// Polls the queue, returning the index of the next slot in the slab that /// should be returned. /// /// A slot should be returned when the associated deadline has been reached. fn poll_idx(&mut self) -> Poll<Option<usize>, Error> { use self::wheel::Stack; let expired = self.expired.pop(&mut self.slab); if expired.is_some() { return Ok(expired.into()); } loop { if let Some(ref mut delay) = self.delay { if !delay.is_elapsed() { try_ready!(delay.poll()); } let now = ::ms(delay.deadline() - self.start, ::Round::Down); self.poll = wheel::Poll::new(now); } self.delay = None; if let Some(idx) = self.wheel.poll(&mut self.poll, &mut self.slab) { return Ok(Some(idx).into()); } if let Some(deadline) = self.next_deadline() { self.delay = Some(self.handle.delay(deadline)); } else { return Ok(None.into()); } } } fn normalize_deadline(&self, when: Instant) -> u64 { let when = if when < self.start { 0 } else { ::ms(when - self.start, ::Round::Up) }; cmp::max(when, self.wheel.elapsed()) } } impl<T> Stream for DelayQueue<T> { type Item = Expired<T>; type Error = Error; fn poll(&mut self) -> Poll<Option<Self::Item>, Error> { let item = try_ready!(self.poll_idx()).map(|idx| { let data = self.slab.remove(idx); debug_assert!(data.next.is_none()); debug_assert!(data.prev.is_none()); Expired { key: Key::new(idx), data: data.inner, deadline: self.start + Duration::from_millis(data.when), } }); Ok(item.into()) } } impl<T> wheel::Stack for Stack<T> { type Owned = usize; type Borrowed = usize; type Store = Slab<Data<T>>; fn is_empty(&self) -> bool { self.head.is_none() } fn push(&mut self, item: Self::Owned, store: &mut Self::Store) { // Ensure the entry is not already in a stack. debug_assert!(store[item].next.is_none()); debug_assert!(store[item].prev.is_none()); // Remove the old head entry let old = self.head.take(); if let Some(idx) = old { store[idx].prev = Some(item); } store[item].next = old; self.head = Some(item) } fn pop(&mut self, store: &mut Self::Store) -> Option<Self::Owned> { if let Some(idx) = self.head { self.head = store[idx].next; if let Some(idx) = self.head { store[idx].prev = None; } store[idx].next = None; debug_assert!(store[idx].prev.is_none()); Some(idx) } else { None } } fn remove(&mut self, item: &Self::Borrowed, store: &mut Self::Store) { assert!(store.contains(*item)); // Ensure that the entry is in fact contained by the stack debug_assert!({ // This walks the full linked list even if an entry is found. let mut next = self.head; let mut contains = false; while let Some(idx) = next { if idx == *item { debug_assert!(!contains); contains = true; } next = store[idx].next; } contains }); if let Some(next) = store[*item].next { store[next].prev = store[*item].prev; } if let Some(prev) = store[*item].prev { store[prev].next = store[*item].next; } else { self.head = store[*item].next; } store[*item].next = None; store[*item].prev = None; } fn when(item: &Self::Borrowed, store: &Self::Store) -> u64 { store[*item].when } } impl<T> Default for Stack<T> { fn default() -> Stack<T> { Stack { head: None, _p: PhantomData, } } } impl Key { pub(crate) fn new(index: usize) -> Key { Key { index } } } impl<T> Expired<T> { /// Returns a reference to the inner value. pub fn get_ref(&self) -> &T { &self.data } /// Returns a mutable reference to the inner value. pub fn get_mut(&mut self) -> &mut T { &mut self.data } /// Consumes `self` and returns the inner value. pub fn into_inner(self) -> T { self.data } }