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-rw-r--r--tokio-util/src/time/wheel/mod.rs314
1 files changed, 314 insertions, 0 deletions
diff --git a/tokio-util/src/time/wheel/mod.rs b/tokio-util/src/time/wheel/mod.rs
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+++ b/tokio-util/src/time/wheel/mod.rs
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+mod level;
+pub(crate) use self::level::Expiration;
+use self::level::Level;
+
+mod stack;
+pub(crate) use self::stack::Stack;
+
+use std::borrow::Borrow;
+use std::usize;
+
+/// Timing wheel implementation.
+///
+/// This type provides the hashed timing wheel implementation that backs `Timer`
+/// and `DelayQueue`.
+///
+/// The structure is generic over `T: Stack`. This allows handling timeout data
+/// being stored on the heap or in a slab. In order to support the latter case,
+/// the slab must be passed into each function allowing the implementation to
+/// lookup timer entries.
+///
+/// See `Timer` documentation for some implementation notes.
+#[derive(Debug)]
+pub(crate) struct Wheel<T> {
+ /// The number of milliseconds elapsed since the wheel started.
+ elapsed: u64,
+
+ /// Timer wheel.
+ ///
+ /// Levels:
+ ///
+ /// * 1 ms slots / 64 ms range
+ /// * 64 ms slots / ~ 4 sec range
+ /// * ~ 4 sec slots / ~ 4 min range
+ /// * ~ 4 min slots / ~ 4 hr range
+ /// * ~ 4 hr slots / ~ 12 day range
+ /// * ~ 12 day slots / ~ 2 yr range
+ levels: Vec<Level<T>>,
+}
+
+/// Number of levels. Each level has 64 slots. By using 6 levels with 64 slots
+/// each, the timer is able to track time up to 2 years into the future with a
+/// precision of 1 millisecond.
+const NUM_LEVELS: usize = 6;
+
+/// The maximum duration of a delay
+const MAX_DURATION: u64 = (1 << (6 * NUM_LEVELS)) - 1;
+
+#[derive(Debug)]
+pub(crate) enum InsertError {
+ Elapsed,
+ Invalid,
+}
+
+/// Poll expirations from the wheel
+#[derive(Debug, Default)]
+pub(crate) struct Poll {
+ now: u64,
+ expiration: Option<Expiration>,
+}
+
+impl<T> Wheel<T>
+where
+ T: Stack,
+{
+ /// Create a new timing wheel
+ pub(crate) fn new() -> Wheel<T> {
+ let levels = (0..NUM_LEVELS).map(Level::new).collect();
+
+ Wheel { elapsed: 0, levels }
+ }
+
+ /// Return the number of milliseconds that have elapsed since the timing
+ /// wheel's creation.
+ pub(crate) fn elapsed(&self) -> u64 {
+ self.elapsed
+ }
+
+ /// Insert an entry into the timing wheel.
+ ///
+ /// # Arguments
+ ///
+ /// * `when`: is the instant at which the entry should be fired. It is
+ /// represented as the number of milliseconds since the creation
+ /// of the timing wheel.
+ ///
+ /// * `item`: The item to insert into the wheel.
+ ///
+ /// * `store`: The slab or `()` when using heap storage.
+ ///
+ /// # Return
+ ///
+ /// Returns `Ok` when the item is successfully inserted, `Err` otherwise.
+ ///
+ /// `Err(Elapsed)` indicates that `when` represents an instant that has
+ /// already passed. In this case, the caller should fire the timeout
+ /// immediately.
+ ///
+ /// `Err(Invalid)` indicates an invalid `when` argument as been supplied.
+ pub(crate) fn insert(
+ &mut self,
+ when: u64,
+ item: T::Owned,
+ store: &mut T::Store,
+ ) -> Result<(), (T::Owned, InsertError)> {
+ if when <= self.elapsed {
+ return Err((item, InsertError::Elapsed));
+ } else if when - self.elapsed > MAX_DURATION {
+ return Err((item, InsertError::Invalid));
+ }
+
+ // Get the level at which the entry should be stored
+ let level = self.level_for(when);
+
+ self.levels[level].add_entry(when, item, store);
+
+ debug_assert!({
+ self.levels[level]
+ .next_expiration(self.elapsed)
+ .map(|e| e.deadline >= self.elapsed)
+ .unwrap_or(true)
+ });
+
+ Ok(())
+ }
+
+ /// Remove `item` from thee timing wheel.
+ pub(crate) fn remove(&mut self, item: &T::Borrowed, store: &mut T::Store) {
+ let when = T::when(item, store);
+ let level = self.level_for(when);
+
+ self.levels[level].remove_entry(when, item, store);
+ }
+
+ /// Instant at which to poll
+ pub(crate) fn poll_at(&self) -> Option<u64> {
+ self.next_expiration().map(|expiration| expiration.deadline)
+ }
+
+ pub(crate) fn poll(&mut self, poll: &mut Poll, store: &mut T::Store) -> Option<T::Owned> {
+ loop {
+ if poll.expiration.is_none() {
+ poll.expiration = self.next_expiration().and_then(|expiration| {
+ if expiration.deadline > poll.now {
+ None
+ } else {
+ Some(expiration)
+ }
+ });
+ }
+
+ match poll.expiration {
+ Some(ref expiration) => {
+ if let Some(item) = self.poll_expiration(expiration, store) {
+ return Some(item);
+ }
+
+ self.set_elapsed(expiration.deadline);
+ }
+ None => {
+ self.set_elapsed(poll.now);
+ return None;
+ }
+ }
+
+ poll.expiration = None;
+ }
+ }
+
+ /// Returns the instant at which the next timeout expires.
+ fn next_expiration(&self) -> Option<Expiration> {
+ // Check all levels
+ for level in 0..NUM_LEVELS {
+ if let Some(expiration) = self.levels[level].next_expiration(self.elapsed) {
+ // There cannot be any expirations at a higher level that happen
+ // before this one.
+ debug_assert!(self.no_expirations_before(level + 1, expiration.deadline));
+
+ return Some(expiration);
+ }
+ }
+
+ None
+ }
+
+ /// Used for debug assertions
+ fn no_expirations_before(&self, start_level: usize, before: u64) -> bool {
+ let mut res = true;
+
+ for l2 in start_level..NUM_LEVELS {
+ if let Some(e2) = self.levels[l2].next_expiration(self.elapsed) {
+ if e2.deadline < before {
+ res = false;
+ }
+ }
+ }
+
+ res
+ }
+
+ pub(crate) fn poll_expiration(
+ &mut self,
+ expiration: &Expiration,
+ store: &mut T::Store,
+ ) -> Option<T::Owned> {
+ while let Some(item) = self.pop_entry(expiration, store) {
+ if expiration.level == 0 {
+ debug_assert_eq!(T::when(item.borrow(), store), expiration.deadline);
+
+ return Some(item);
+ } else {
+ let when = T::when(item.borrow(), store);
+
+ let next_level = expiration.level - 1;
+
+ self.levels[next_level].add_entry(when, item, store);
+ }
+ }
+
+ None
+ }
+
+ fn set_elapsed(&mut self, when: u64) {
+ assert!(
+ self.elapsed <= when,
+ "elapsed={:?}; when={:?}",
+ self.elapsed,
+ when
+ );
+
+ if when > self.elapsed {
+ self.elapsed = when;
+ }
+ }
+
+ fn pop_entry(&mut self, expiration: &Expiration, store: &mut T::Store) -> Option<T::Owned> {
+ self.levels[expiration.level].pop_entry_slot(expiration.slot, store)
+ }
+
+ fn level_for(&self, when: u64) -> usize {
+ level_for(self.elapsed, when)
+ }
+}
+
+fn level_for(elapsed: u64, when: u64) -> usize {
+ let masked = elapsed ^ when;
+
+ assert!(masked != 0, "elapsed={}; when={}", elapsed, when);
+
+ let leading_zeros = masked.leading_zeros() as usize;
+ let significant = 63 - leading_zeros;
+ significant / 6
+}
+
+impl Poll {
+ pub(crate) fn new(now: u64) -> Poll {
+ Poll {
+ now,
+ expiration: None,
+ }
+ }
+}
+
+#[cfg(all(test, not(loom)))]
+mod test {
+ use super::*;
+
+ #[test]
+ fn test_level_for() {
+ for pos in 1..64 {
+ assert_eq!(
+ 0,
+ level_for(0, pos),
+ "level_for({}) -- binary = {:b}",
+ pos,
+ pos
+ );
+ }
+
+ for level in 1..5 {
+ for pos in level..64 {
+ let a = pos * 64_usize.pow(level as u32);
+ assert_eq!(
+ level,
+ level_for(0, a as u64),
+ "level_for({}) -- binary = {:b}",
+ a,
+ a
+ );
+
+ if pos > level {
+ let a = a - 1;
+ assert_eq!(
+ level,
+ level_for(0, a as u64),
+ "level_for({}) -- binary = {:b}",
+ a,
+ a
+ );
+ }
+
+ if pos < 64 {
+ let a = a + 1;
+ assert_eq!(
+ level,
+ level_for(0, a as u64),
+ "level_for({}) -- binary = {:b}",
+ a,
+ a
+ );
+ }
+ }
+ }
+ }
+}
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