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//! Tracks minimal sets of mutually incomparable elements of a partial order. // use progress::CountMap; use order::PartialOrder; /// A set of mutually incomparable elements. /// /// An antichain is a set of partially ordered elements, each of which is incomparable to the others. /// This antichain implementation allows you to repeatedly introduce elements to the antichain, and /// which will evict larger elements to maintain the *minimal* antichain, those incomparable elements /// no greater than any other element. #[derive(Default, Clone, Debug)] pub struct Antichain<T> { elements: Vec<T> } impl<T: PartialOrder> Antichain<T> { /// Updates the `Antichain` if the element is not greater than or equal to some present element. /// /// Returns true if element is added to the set pub fn insert(&mut self, element: T) -> bool { if !self.elements.iter().any(|x| x.less_equal(&element)) { self.elements.retain(|x| !element.less_equal(x)); self.elements.push(element); true } else { false } } /// Creates a new empty `Antichain`. pub fn new() -> Antichain<T> { Antichain { elements: Vec::new() } } /// Creates a new singleton `Antichain`. pub fn from_elem(element: T) -> Antichain<T> { Antichain { elements: vec![element] } } /// Clears the contents of the antichain. pub fn clear(&mut self) { self.elements.clear() } /// Returns true if any item in the antichain is strictly less than the argument. #[inline] pub fn less_than(&self, time: &T) -> bool { self.elements.iter().any(|x| x.less_than(time)) } /// Returns true if any item in the antichain is less than or equal to the argument. #[inline] pub fn less_equal(&self, time: &T) -> bool { self.elements.iter().any(|x| x.less_equal(time)) } /// Returns true if every element of `other` is greater or equal to some element of `self`. #[inline] pub fn dominates(&self, other: &Antichain<T>) -> bool { other.elements().iter().all(|t2| self.elements().iter().any(|t1| t1.less_equal(t2))) } /// Reveals the elements in the antichain. #[inline] pub fn elements(&self) -> &[T] { &self.elements[..] } } /// An antichain based on a multiset whose elements frequencies can be updated. /// /// The `MutableAntichain` maintains frequencies for many elements of type `T`, and exposes the set /// of elements with positive count not greater than any other elements with positive count. The /// antichain may both advance and retreat; the changes do not all need to be to elements greater or /// equal to some elements of the frontier. /// /// The type `T` must implement `PartialOrder` as well as `Ord`. The implementation of the `Ord` trait /// is used to efficiently organize the updates for cancellation, and to efficiently determine the lower /// bounds, and only needs to not contradict the `PartialOrder` implementation (that is, if `PartialOrder` /// orders two elements, the so does the `Ord` implementation). /// /// The `MutableAntichain` implementation is done with the intent that updates to it are done in batches, /// and it is acceptable to rebuild the frontier from scratch when a batch of updates change it. This means /// that it can be expensive to maintain a large number of counts and change few elements near the frontier. /// /// There is an `update_dirty` method for single updates that leave the `MutableAntichain` in a dirty state, /// but I strongly recommend against using them unless you must (on part of timely progress tracking seems /// to be greatly simplified by access to this) #[derive(Default, Debug, Clone)] pub struct MutableAntichain<T: PartialOrder+Ord> { dirty: usize, updates: Vec<(T, i64)>, frontier: Vec<T>, frontier_temp: Vec<T>, } impl<T: PartialOrder+Ord+Clone+'static> MutableAntichain<T> { /// Creates a new empty `MutableAntichain`. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let frontier = MutableAntichain::<usize>::new(); /// assert!(frontier.is_empty()); ///``` #[inline] pub fn new() -> MutableAntichain<T> { MutableAntichain { dirty: 0, updates: Vec::new(), frontier: Vec::new(), frontier_temp: Vec::new(), } } /// Removes all elements. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::<usize>::new(); /// frontier.clear(); /// assert!(frontier.is_empty()); ///``` #[inline] pub fn clear(&mut self) { self.dirty = 0; self.updates.clear(); self.frontier.clear(); self.frontier_temp.clear(); } /// Reveals the minimal elements with positive count. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::<usize>::new(); /// assert!(frontier.frontier().len() == 0); ///``` #[inline] pub fn frontier(&self) -> &[T] { debug_assert_eq!(self.dirty, 0); &self.frontier } /// Creates a new singleton `MutableAntichain`. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::new_bottom(0u64); /// assert_eq!(frontier.frontier(), &[0u64]); ///``` #[inline] pub fn new_bottom(bottom: T) -> MutableAntichain<T> { MutableAntichain { dirty: 0, updates: vec![(bottom.clone(), 1)], frontier: vec![bottom.clone()], frontier_temp: Vec::new(), } } /// Returns true if there are no elements in the `MutableAntichain`. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::<usize>::new(); /// assert!(frontier.is_empty()); ///``` #[inline] pub fn is_empty(&self) -> bool { debug_assert_eq!(self.dirty, 0); self.frontier.is_empty() } /// Returns true if any item in the `MutableAntichain` is strictly less than the argument. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::new_bottom(1u64); /// assert!(!frontier.less_than(&0)); /// assert!(!frontier.less_than(&1)); /// assert!(frontier.less_than(&2)); ///``` #[inline] pub fn less_than(&self, time: &T) -> bool { debug_assert_eq!(self.dirty, 0); self.frontier.iter().any(|x| x.less_than(time)) } /// Returns true if any item in the `MutableAntichain` is less than or equal to the argument. #[inline] /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::new_bottom(1u64); /// assert!(!frontier.less_equal(&0)); /// assert!(frontier.less_equal(&1)); /// assert!(frontier.less_equal(&2)); ///``` pub fn less_equal(&self, time: &T) -> bool { debug_assert_eq!(self.dirty, 0); self.frontier.iter().any(|x| x.less_equal(time)) } /// Allows a single-element push, but dirties the antichain and prevents inspection until cleaned. /// /// At the moment inspection is prevented via panic, so best be careful (this should probably be fixed). /// It is *very* important if you want to use this method that very soon afterwards you call something /// akin to `update_iter`, perhaps with a `None` argument if you have no more data, as this method will /// tidy up the internal representation. #[inline] pub fn update_dirty(&mut self, time: T, delta: i64) { self.updates.push((time, delta)); self.dirty += 1; } /// Applies updates to the antichain and applies `action` to each frontier change. /// /// This method applies a batch of updates and if any affects the frontier it is rebuilt. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::new_bottom(1u64); /// frontier.update_iter(vec![(1, -1), (2, 1)].into_iter()); /// assert_eq!(frontier.frontier(), &[2]); ///``` #[inline] pub fn update_iter<I>(&mut self, updates: I) where I: IntoIterator<Item = (T, i64)> { self.update_iter_and(updates, |_,_| { }); } /// Applies updates to the antichain and applies `action` to each frontier change. /// /// This method applies a batch of updates and if any affects the frontier it is rebuilt. /// Once rebuilt, `action` is called with the corresponding changes to the frontier, which /// should be various times and `{ +1, -1 }` differences. /// /// #Examples /// ///``` /// use timely::progress::frontier::MutableAntichain; /// /// let mut frontier = MutableAntichain::new_bottom(1u64); /// let mut changes = Vec::new(); /// frontier.update_iter_and(vec![(1, -1), (2, 1)].into_iter(), |time, diff| { /// changes.push((time.clone(), diff)); /// }); /// assert_eq!(frontier.frontier(), &[2]); /// changes.sort(); /// assert_eq!(&changes[..], &[(1, -1), (2, 1)]); ///``` #[inline] pub fn update_iter_and<I, A>(&mut self, updates: I, action: A) where I: IntoIterator<Item = (T, i64)>, A: FnMut(&T, i64) { // track whether a rebuild is needed. let mut rebuild_required = false; for (time, delta) in updates { self.updates.push((time, delta)); self.dirty += 1; } // determine if recently pushed data requires rebuilding the frontier. // note: this may be required even with an empty iterator, due to dirty data in self.updates. while self.dirty > 0 { let time = &self.updates[self.updates.len() - self.dirty].0; let delta = self.updates[self.updates.len() - self.dirty].1; let beyond_frontier = self.frontier.iter().any(|f| f.less_than(time)); let before_frontier = !self.frontier.iter().any(|f| f.less_equal(time)); rebuild_required = rebuild_required || !(beyond_frontier || (delta < 0 && before_frontier)); self.dirty -= 1; } if rebuild_required { self.rebuild_and(action); } } /// Sorts and consolidates `self.updates` and applies `action` to any frontier changes. /// /// This method is meant to be used for bulk updates to the frontier, and does more work than one might do /// for single updates, but is meant to be an efficient way to process multiple updates together. This is /// especially true when we want to apply very large numbers of updates. fn rebuild_and<A: FnMut(&T, i64)>(&mut self, mut action: A) { // sort and consolidate updates; retain non-zero accumulations. if !self.updates.is_empty() { self.updates.sort_by(|x,y| x.0.cmp(&y.0)); for i in 0 .. self.updates.len() - 1 { if self.updates[i].0 == self.updates[i+1].0 { self.updates[i+1].1 += self.updates[i].1; self.updates[i].1 = 0; } } self.updates.retain(|x| x.1 != 0); } // build new frontier using strictly positive times. // as the times are sorted, we don't need to worry that we might displace frontier elements. for time in self.updates.iter().filter(|x| x.1 > 0) { if !self.frontier_temp.iter().any(|f| f.less_than(&time.0)) { self.frontier_temp.push(time.0.clone()); } } // TODO: This is quadratic in the frontier size, but could be linear (with a merge). for time in self.frontier.iter() { if !self.frontier_temp.contains(time) { action(time, -1); } } ::std::mem::swap(&mut self.frontier, &mut self.frontier_temp); for time in self.frontier.iter() { if !self.frontier_temp.contains(time) { action(time, 1); } } self.frontier_temp.clear(); } }