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//! Timer implementation. //! //! This module contains the types needed to run a timer. //! //! The [`Timer`] type runs the timer logic. It holds all the necessary state //! to track all associated [`Delay`] instances and delivering notifications //! once the deadlines are reached. //! //! The [`Handle`] type is a reference to a [`Timer`] instance. This type is //! `Clone`, `Send`, and `Sync`. This type is used to create instances of //! [`Delay`]. //! //! The [`Now`] trait describes how to get an [`Instant`] representing the //! current moment in time. [`SystemNow`] is the default implementation, where //! [`Now::now`] is implemented by calling [`Instant::now`]. //! //! [`Timer`] is generic over [`Now`]. This allows the source of time to be //! customized. This ability is especially useful in tests and any environment //! where determinism is necessary. //! //! Note, when using the Tokio runtime, the [`Timer`] does not need to be manually //! setup as the runtime comes pre-configured with a [`Timer`] instance. //! //! [`Timer`]: struct.Timer.html //! [`Handle`]: struct.Handle.html //! [`Delay`]: ../struct.Delay.html //! [`Now`]: ../clock/trait.Now.html //! [`Now::now`]: ../clock/trait.Now.html#method.now //! [`SystemNow`]: struct.SystemNow.html //! [`Instant`]: https://doc.rust-lang.org/std/time/struct.Instant.html //! [`Instant::now`]: https://doc.rust-lang.org/std/time/struct.Instant.html#method.now // This allows the usage of the old `Now` trait. #![allow(deprecated)] mod atomic_stack; mod entry; mod handle; mod now; mod registration; mod stack; use self::atomic_stack::AtomicStack; use self::entry::Entry; use self::stack::Stack; pub(crate) use self::handle::HandlePriv; pub use self::handle::{set_default, with_default, DefaultGuard, Handle}; pub use self::now::{Now, SystemNow}; pub(crate) use self::registration::Registration; use atomic::AtomicU64; use wheel; use Error; use tokio_executor::park::{Park, ParkThread, Unpark}; use std::sync::atomic::AtomicUsize; use std::sync::atomic::Ordering::SeqCst; use std::sync::Arc; use std::time::{Duration, Instant}; use std::usize; use std::{cmp, fmt}; /// Timer implementation that drives [`Delay`], [`Interval`], and [`Timeout`]. /// /// A `Timer` instance tracks the state necessary for managing time and /// notifying the [`Delay`] instances once their deadlines are reached. /// /// It is expected that a single `Timer` instance manages many individual /// [`Delay`] instances. The `Timer` implementation is thread-safe and, as such, /// is able to handle callers from across threads. /// /// Callers do not use `Timer` directly to create [`Delay`] instances. Instead, /// [`Handle`][Handle.struct] is used. A handle for the timer instance is obtained by calling /// [`handle`]. [`Handle`][Handle.struct] is the type that implements `Clone` and is `Send + /// Sync`. /// /// After creating the `Timer` instance, the caller must repeatedly call /// [`turn`]. The timer will perform no work unless [`turn`] is called /// repeatedly. /// /// The `Timer` has a resolution of one millisecond. Any unit of time that falls /// between milliseconds are rounded up to the next millisecond. /// /// When the `Timer` instance is dropped, any outstanding [`Delay`] instance that /// has not elapsed will be notified with an error. At this point, calling /// `poll` on the [`Delay`] instance will result in `Err` being returned. /// /// # Implementation /// /// `Timer` is based on the [paper by Varghese and Lauck][paper]. /// /// A hashed timing wheel is a vector of slots, where each slot handles a time /// slice. As time progresses, the timer walks over the slot for the current /// instant, and processes each entry for that slot. When the timer reaches the /// end of the wheel, it starts again at the beginning. /// /// The `Timer` implementation maintains six wheels arranged in a set of levels. /// As the levels go up, the slots of the associated wheel represent larger /// intervals of time. At each level, the wheel has 64 slots. Each slot covers a /// range of time equal to the wheel at the lower level. At level zero, each /// slot represents one millisecond of time. /// /// The wheels are: /// /// * Level 0: 64 x 1 millisecond slots. /// * Level 1: 64 x 64 millisecond slots. /// * Level 2: 64 x ~4 second slots. /// * Level 3: 64 x ~4 minute slots. /// * Level 4: 64 x ~4 hour slots. /// * Level 5: 64 x ~12 day slots. /// /// When the timer processes entries at level zero, it will notify all the /// [`Delay`] instances as their deadlines have been reached. For all higher /// levels, all entries will be redistributed across the wheel at the next level /// down. Eventually, as time progresses, entries will [`Delay`] instances will /// either be canceled (dropped) or their associated entries will reach level /// zero and be notified. /// /// [`Delay`]: ../struct.Delay.html /// [`Interval`]: ../struct.Interval.html /// [`Timeout`]: ../struct.Timeout.html /// [paper]: http://www.cs.columbia.edu/~nahum/w6998/papers/ton97-timing-wheels.pdf /// [`handle`]: #method.handle /// [`turn`]: #method.turn /// [Handle.struct]: struct.Handle.html #[derive(Debug)] pub struct Timer<T, N = SystemNow> { /// Shared state inner: Arc<Inner>, /// Timer wheel wheel: wheel::Wheel<Stack>, /// Thread parker. The `Timer` park implementation delegates to this. park: T, /// Source of "now" instances now: N, } /// Return value from the `turn` method on `Timer`. /// /// Currently this value doesn't actually provide any functionality, but it may /// in the future give insight into what happened during `turn`. #[derive(Debug)] pub struct Turn(()); /// Timer state shared between `Timer`, `Handle`, and `Registration`. pub(crate) struct Inner { /// The instant at which the timer started running. start: Instant, /// The last published timer `elapsed` value. elapsed: AtomicU64, /// Number of active timeouts num: AtomicUsize, /// Head of the "process" linked list. process: AtomicStack, /// Unparks the timer thread. unpark: Box<dyn Unpark>, } /// Maximum number of timeouts the system can handle concurrently. const MAX_TIMEOUTS: usize = usize::MAX >> 1; // ===== impl Timer ===== impl<T> Timer<T> where T: Park, { /// Create a new `Timer` instance that uses `park` to block the current /// thread. /// /// Once the timer has been created, a handle can be obtained using /// [`handle`]. The handle is used to create `Delay` instances. /// /// Use `default` when constructing a `Timer` using the default `park` /// instance. /// /// [`handle`]: #method.handle pub fn new(park: T) -> Self { Timer::new_with_now(park, SystemNow::new()) } } impl<T, N> Timer<T, N> { /// Returns a reference to the underlying `Park` instance. pub fn get_park(&self) -> &T { &self.park } /// Returns a mutable reference to the underlying `Park` instance. pub fn get_park_mut(&mut self) -> &mut T { &mut self.park } } impl<T, N> Timer<T, N> where T: Park, N: Now, { /// Create a new `Timer` instance that uses `park` to block the current /// thread and `now` to get the current `Instant`. /// /// Specifying the source of time is useful when testing. pub fn new_with_now(park: T, mut now: N) -> Self { let unpark = Box::new(park.unpark()); Timer { inner: Arc::new(Inner::new(now.now(), unpark)), wheel: wheel::Wheel::new(), park, now, } } /// Returns a handle to the timer. /// /// The `Handle` is how `Delay` instances are created. The `Delay` instances /// can either be created directly or the `Handle` instance can be passed to /// `with_default`, setting the timer as the default timer for the execution /// context. pub fn handle(&self) -> Handle { Handle::new(Arc::downgrade(&self.inner)) } /// Performs one iteration of the timer loop. /// /// This function must be called repeatedly in order for the `Timer` /// instance to make progress. This is where the work happens. /// /// The `Timer` will use the `Park` instance that was specified in [`new`] /// to block the current thread until the next `Delay` instance elapses. One /// call to `turn` results in at most one call to `park.park()`. /// /// # Return /// /// On success, `Ok(Turn)` is returned, where `Turn` is a placeholder type /// that currently does nothing but may, in the future, have functions add /// to provide information about the call to `turn`. /// /// If the call to `park.park()` fails, then `Err` is returned with the /// error. /// /// [`new`]: #method.new pub fn turn(&mut self, max_wait: Option<Duration>) -> Result<Turn, T::Error> { match max_wait { Some(timeout) => self.park_timeout(timeout)?, None => self.park()?, } Ok(Turn(())) } /// Converts an `Expiration` to an `Instant`. fn expiration_instant(&self, when: u64) -> Instant { self.inner.start + Duration::from_millis(when) } /// Run timer related logic fn process(&mut self) { let now = ::ms(self.now.now() - self.inner.start, ::Round::Down); let mut poll = wheel::Poll::new(now); while let Some(entry) = self.wheel.poll(&mut poll, &mut ()) { let when = entry.when_internal().expect("invalid internal entry state"); // Fire the entry entry.fire(when); // Track that the entry has been fired entry.set_when_internal(None); } // Update the elapsed cache self.inner.elapsed.store(self.wheel.elapsed(), SeqCst); } /// Process the entry queue /// /// This handles adding and canceling timeouts. fn process_queue(&mut self) { for entry in self.inner.process.take() { match (entry.when_internal(), entry.load_state()) { (None, None) => { // Nothing to do } (Some(_), None) => { // Remove the entry self.clear_entry(&entry); } (None, Some(when)) => { // Queue the entry self.add_entry(entry, when); } (Some(_), Some(next)) => { self.clear_entry(&entry); self.add_entry(entry, next); } } } } fn clear_entry(&mut self, entry: &Arc<Entry>) { self.wheel.remove(entry, &mut ()); entry.set_when_internal(None); } /// Fire the entry if it needs to, otherwise queue it to be processed later. /// /// Returns `None` if the entry was fired. fn add_entry(&mut self, entry: Arc<Entry>, when: u64) { use wheel::InsertError; entry.set_when_internal(Some(when)); match self.wheel.insert(when, entry, &mut ()) { Ok(_) => {} Err((entry, InsertError::Elapsed)) => { // The entry's deadline has elapsed, so fire it and update the // internal state accordingly. entry.set_when_internal(None); entry.fire(when); } Err((entry, InsertError::Invalid)) => { // The entry's deadline is invalid, so error it and update the // internal state accordingly. entry.set_when_internal(None); entry.error(); } } } } impl Default for Timer<ParkThread, SystemNow> { fn default() -> Self { Timer::new(ParkThread::new()) } } impl<T, N> Park for Timer<T, N> where T: Park, N: Now, { type Unpark = T::Unpark; type Error = T::Error; fn unpark(&self) -> Self::Unpark { self.park.unpark() } fn park(&mut self) -> Result<(), Self::Error> { self.process_queue(); match self.wheel.poll_at() { Some(when) => { let now = self.now.now(); let deadline = self.expiration_instant(when); if deadline > now { self.park.park_timeout(deadline - now)?; } else { self.park.park_timeout(Duration::from_secs(0))?; } } None => { self.park.park()?; } } self.process(); Ok(()) } fn park_timeout(&mut self, duration: Duration) -> Result<(), Self::Error> { self.process_queue(); match self.wheel.poll_at() { Some(when) => { let now = self.now.now(); let deadline = self.expiration_instant(when); if deadline > now { self.park.park_timeout(cmp::min(deadline - now, duration))?; } else { self.park.park_timeout(Duration::from_secs(0))?; } } None => { self.park.park_timeout(duration)?; } } self.process(); Ok(()) } } impl<T, N> Drop for Timer<T, N> { fn drop(&mut self) { use std::u64; // Shutdown the stack of entries to process, preventing any new entries // from being pushed. self.inner.process.shutdown(); // Clear the wheel, using u64::MAX allows us to drain everything let mut poll = wheel::Poll::new(u64::MAX); while let Some(entry) = self.wheel.poll(&mut poll, &mut ()) { entry.error(); } } } // ===== impl Inner ===== impl Inner { fn new(start: Instant, unpark: Box<dyn Unpark>) -> Inner { Inner { num: AtomicUsize::new(0), elapsed: AtomicU64::new(0), process: AtomicStack::new(), start, unpark, } } fn elapsed(&self) -> u64 { self.elapsed.load(SeqCst) } /// Increment the number of active timeouts fn increment(&self) -> Result<(), Error> { let mut curr = self.num.load(SeqCst); loop { if curr == MAX_TIMEOUTS { return Err(Error::at_capacity()); } let actual = self.num.compare_and_swap(curr, curr + 1, SeqCst); if curr == actual { return Ok(()); } curr = actual; } } /// Decrement the number of active timeouts fn decrement(&self) { let prev = self.num.fetch_sub(1, SeqCst); debug_assert!(prev <= MAX_TIMEOUTS); } fn queue(&self, entry: &Arc<Entry>) -> Result<(), Error> { if self.process.push(entry)? { // The timer is notified so that it can process the timeout self.unpark.unpark(); } Ok(()) } fn normalize_deadline(&self, deadline: Instant) -> u64 { if deadline < self.start { return 0; } ::ms(deadline - self.start, ::Round::Up) } } impl fmt::Debug for Inner { fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result { fmt.debug_struct("Inner").finish() } }