| // Copyright (c) 2019 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| #ifndef QUICHE_QUIC_CORE_QUIC_INTERVAL_DEQUE_H_ |
| #define QUICHE_QUIC_CORE_QUIC_INTERVAL_DEQUE_H_ |
| |
| #include <algorithm> |
| |
| #include "absl/types/optional.h" |
| #include "quic/core/quic_circular_deque.h" |
| #include "quic/core/quic_interval.h" |
| #include "quic/core/quic_types.h" |
| #include "quic/platform/api/quic_bug_tracker.h" |
| #include "quic/platform/api/quic_export.h" |
| #include "quic/platform/api/quic_logging.h" |
| |
| namespace quic { |
| |
| namespace test { |
| class QuicIntervalDequePeer; |
| } // namespace test |
| |
| // QuicIntervalDeque<T, C> is a templated wrapper container, wrapping random |
| // access data structures. The wrapper allows items to be added to the |
| // underlying container with intervals associated with each item. The intervals |
| // _should_ be added already sorted and represent searchable indices. The search |
| // is optimized for sequential usage. |
| // |
| // As the intervals are to be searched sequentially the search for the next |
| // interval can be achieved in O(1), by simply remembering the last interval |
| // consumed. The structure also checks for an "off-by-one" use case wherein the |
| // |cached_index_| is off by one index as the caller didn't call operator |++| |
| // to increment the index. Other intervals can be found in O(log(n)) as they are |
| // binary searchable. A use case for this structure is packet buffering: Packets |
| // are sent sequentially but can sometimes needed for retransmission. The |
| // packets and their payloads are added with associated intervals representing |
| // data ranges they carry. When a user asks for a particular interval it's very |
| // likely they are requesting the next sequential interval, receiving it in O(1) |
| // time. Updating the sequential index is done automatically through the |
| // |DataAt| method and its iterator operator |++|. |
| // |
| // The intervals are represented using the usual C++ STL convention, namely as |
| // the half-open QuicInterval [min, max). A point p is considered to be |
| // contained in the QuicInterval iff p >= min && p < max. One consequence of |
| // this definition is that for any non-empty QuicInterval, min is contained in |
| // the QuicInterval but max is not. There is no canonical representation for the |
| // empty QuicInterval; and empty intervals are forbidden from being added to |
| // this container as they would be unsearchable. |
| // |
| // The type T is required to be copy-constructable or move-constructable. The |
| // type T is also expected to have an |interval()| method returning a |
| // QuicInterval<std::size> for the particular value. The type C is required to |
| // be a random access container supporting the methods |pop_front|, |push_back|, |
| // |operator[]|, |size|, and iterator support for |std::lower_bound| eg. a |
| // |deque| or |vector|. |
| // |
| // The QuicIntervalDeque<T, C>, like other C++ STL random access containers, |
| // doesn't have any explicit support for any equality operators. |
| // |
| // |
| // Examples with internal state: |
| // |
| // // An example class to be stored inside the Interval Deque. |
| // struct IntervalVal { |
| // const int32_t val; |
| // const size_t interval_begin, interval_end; |
| // QuicInterval<size_t> interval(); |
| // }; |
| // typedef IntervalVal IV; |
| // QuicIntervialDeque<IntervalValue> deque; |
| // |
| // // State: |
| // // cached_index -> None |
| // // container -> {} |
| // |
| // // Add interval items |
| // deque.PushBack(IV(val: 0, interval_begin: 0, interval_end: 10)); |
| // deque.PushBack(IV(val: 1, interval_begin: 20, interval_end: 25)); |
| // deque.PushBack(IV(val: 2, interval_begin: 25, interval_end: 30)); |
| // |
| // // State: |
| // // cached_index -> 0 |
| // // container -> {{0, [0, 10)}, {1, [20, 25)}, {2, [25, 30)}} |
| // |
| // // Look for 0 and return [0, 10). Time: O(1) |
| // auto it = deque.DataAt(0); |
| // assert(it->val == 0); |
| // it++; // Increment and move the |cached_index_| over [0, 10) to [20, 25). |
| // assert(it->val == 1); |
| // |
| // // State: |
| // // cached_index -> 1 |
| // // container -> {{0, [0, 10)}, {1, [20, 25)}, {2, [25, 30)}} |
| // |
| // // Look for 20 and return [20, 25). Time: O(1) |
| // auto it = deque.DataAt(20); // |cached_index_| remains unchanged. |
| // assert(it->val == 1); |
| // |
| // // State: |
| // // cached_index -> 1 |
| // // container -> {{0, [0, 10)}, {1, [20, 25)}, {2, [25, 30)}} |
| // |
| // // Look for 15 and return deque.DataEnd(). Time: O(log(n)) |
| // auto it = deque.DataAt(15); // |cached_index_| remains unchanged. |
| // assert(it == deque.DataEnd()); |
| // |
| // // Look for 25 and return [25, 30). Time: O(1) with off-by-one. |
| // auto it = deque.DataAt(25); // |cached_index_| is updated to 2. |
| // assert(it->val == 2); |
| // it++; // |cached_index_| is set to |None| as all data has been iterated. |
| // |
| // |
| // // State: |
| // // cached_index -> None |
| // // container -> {{0, [0, 10)}, {1, [20, 25)}, {2, [25, 30)}} |
| // |
| // // Look again for 0 and return [0, 10). Time: O(log(n)) |
| // auto it = deque.DataAt(0); |
| // |
| // |
| // deque.PopFront(); // Pop -> {0, [0, 10)} |
| // |
| // // State: |
| // // cached_index -> None |
| // // container -> {{1, [20, 25)}, {2, [25, 30)}} |
| // |
| // deque.PopFront(); // Pop -> {1, [20, 25)} |
| // |
| // // State: |
| // // cached_index -> None |
| // // container -> {{2, [25, 30)}} |
| // |
| // deque.PushBack(IV(val: 3, interval_begin: 35, interval_end: 50)); |
| // |
| // // State: |
| // // cached_index -> 1 |
| // // container -> {{2, [25, 30)}, {3, [35, 50)}} |
| |
| template <class T, class C = QUIC_NO_EXPORT QuicCircularDeque<T>> |
| class QUIC_NO_EXPORT QuicIntervalDeque { |
| public: |
| class QUIC_NO_EXPORT Iterator { |
| public: |
| // Used by |std::lower_bound| |
| using iterator_category = std::forward_iterator_tag; |
| using value_type = T; |
| using difference_type = std::ptrdiff_t; |
| using pointer = T*; |
| using reference = T&; |
| |
| // Every increment of the iterator will increment the |cached_index_| if |
| // |index_| is larger than the current |cached_index_|. |index_| is bounded |
| // at |deque_.size()| and any attempt to increment above that will be |
| // ignored. Once an iterator has iterated all elements the |cached_index_| |
| // will be reset. |
| Iterator(std::size_t index, QuicIntervalDeque* deque) |
| : index_(index), deque_(deque) {} |
| // Only the ++ operator attempts to update the cached index. Other operators |
| // are used by |lower_bound| to binary search and are thus private. |
| Iterator& operator++() { |
| // Don't increment when we are at the end. |
| const std::size_t container_size = deque_->container_.size(); |
| if (index_ >= container_size) { |
| QUIC_BUG << "Iterator out of bounds."; |
| return *this; |
| } |
| index_++; |
| if (deque_->cached_index_.has_value()) { |
| const std::size_t cached_index = deque_->cached_index_.value(); |
| // If all items are iterated then reset the |cached_index_| |
| if (index_ == container_size) { |
| deque_->cached_index_.reset(); |
| } else { |
| // Otherwise the new |cached_index_| is the max of itself and |index_| |
| if (cached_index < index_) { |
| deque_->cached_index_ = index_; |
| } |
| } |
| } |
| return *this; |
| } |
| Iterator operator++(int) { |
| Iterator copy = *this; |
| ++(*this); |
| return copy; |
| } |
| reference operator*() { return deque_->container_[index_]; } |
| reference operator*() const { return deque_->container_[index_]; } |
| pointer operator->() { return &deque_->container_[index_]; } |
| bool operator==(const Iterator& rhs) const { |
| return index_ == rhs.index_ && deque_ == rhs.deque_; |
| } |
| bool operator!=(const Iterator& rhs) const { return !(*this == rhs); } |
| |
| private: |
| // A set of private operators for |std::lower_bound| |
| Iterator operator+(difference_type amount) const { |
| Iterator copy = *this; |
| copy.index_ += amount; |
| QUICHE_DCHECK(copy.index_ < copy.deque_->size()); |
| return copy; |
| } |
| Iterator& operator+=(difference_type amount) { |
| index_ += amount; |
| QUICHE_DCHECK(index_ < deque_->size()); |
| return *this; |
| } |
| difference_type operator-(const Iterator& rhs) const { |
| return static_cast<difference_type>(index_) - |
| static_cast<difference_type>(rhs.index_); |
| } |
| |
| // |index_| is the index of the item in |*deque_|. |
| std::size_t index_; |
| // |deque_| is a pointer to the container the iterator came from. |
| QuicIntervalDeque* deque_; |
| |
| friend class QuicIntervalDeque; |
| }; |
| |
| QuicIntervalDeque(); |
| |
| // Adds an item to the underlying container. The |item|'s interval _should_ be |
| // strictly greater than the last interval added. |
| void PushBack(T&& item); |
| void PushBack(const T& item); |
| // Removes the front/top of the underlying container and the associated |
| // interval. |
| void PopFront(); |
| // Returns an iterator to the beginning of the data. The iterator will move |
| // the |cached_index_| as the iterator moves. |
| Iterator DataBegin(); |
| // Returns an iterator to the end of the data. |
| Iterator DataEnd(); |
| // Returns an iterator pointing to the item in |interval_begin|. The iterator |
| // will move the |cached_index_| as the iterator moves. |
| Iterator DataAt(const std::size_t interval_begin); |
| |
| // Returns the number of items contained inside the structure. |
| std::size_t Size() const; |
| // Returns whether the structure is empty. |
| bool Empty() const; |
| |
| private: |
| struct QUIC_NO_EXPORT IntervalCompare { |
| bool operator()(const T& item, std::size_t interval_begin) const { |
| return item.interval().max() <= interval_begin; |
| } |
| }; |
| |
| template <class U> |
| void PushBackUniversal(U&& item); |
| |
| Iterator Search(const std::size_t interval_begin, |
| const std::size_t begin_index, |
| const std::size_t end_index); |
| |
| // For accessing the |cached_index_| |
| friend class test::QuicIntervalDequePeer; |
| |
| C container_; |
| absl::optional<std::size_t> cached_index_; |
| }; |
| |
| template <class T, class C> |
| QuicIntervalDeque<T, C>::QuicIntervalDeque() {} |
| |
| template <class T, class C> |
| void QuicIntervalDeque<T, C>::PushBack(T&& item) { |
| PushBackUniversal(std::move(item)); |
| } |
| |
| template <class T, class C> |
| void QuicIntervalDeque<T, C>::PushBack(const T& item) { |
| PushBackUniversal(item); |
| } |
| |
| template <class T, class C> |
| void QuicIntervalDeque<T, C>::PopFront() { |
| if (container_.size() == 0) { |
| QUIC_BUG << "Trying to pop from an empty container."; |
| return; |
| } |
| container_.pop_front(); |
| if (container_.size() == 0) { |
| cached_index_.reset(); |
| } |
| if (cached_index_.value_or(0) > 0) { |
| cached_index_ = cached_index_.value() - 1; |
| } |
| } |
| |
| template <class T, class C> |
| typename QuicIntervalDeque<T, C>::Iterator |
| QuicIntervalDeque<T, C>::DataBegin() { |
| return Iterator(0, this); |
| } |
| |
| template <class T, class C> |
| typename QuicIntervalDeque<T, C>::Iterator QuicIntervalDeque<T, C>::DataEnd() { |
| return Iterator(container_.size(), this); |
| } |
| |
| template <class T, class C> |
| typename QuicIntervalDeque<T, C>::Iterator QuicIntervalDeque<T, C>::DataAt( |
| const std::size_t interval_begin) { |
| // No |cached_index_| value means all items can be searched. |
| if (!cached_index_.has_value()) { |
| return Search(interval_begin, 0, container_.size()); |
| } |
| |
| const std::size_t cached_index = cached_index_.value(); |
| QUICHE_DCHECK(cached_index < container_.size()); |
| |
| const QuicInterval<size_t> cached_interval = |
| container_[cached_index].interval(); |
| // Does our cached index point directly to what we want? |
| if (cached_interval.Contains(interval_begin)) { |
| return Iterator(cached_index, this); |
| } |
| |
| // Are we off-by-one? |
| const std::size_t next_index = cached_index + 1; |
| if (next_index < container_.size()) { |
| if (container_[next_index].interval().Contains(interval_begin)) { |
| cached_index_ = next_index; |
| return Iterator(next_index, this); |
| } |
| } |
| |
| // Small optimization: |
| // Determine if we should binary search above or below the cached interval. |
| const std::size_t cached_begin = cached_interval.min(); |
| bool looking_below = interval_begin < cached_begin; |
| const std::size_t lower = looking_below ? 0 : cached_index + 1; |
| const std::size_t upper = looking_below ? cached_index : container_.size(); |
| Iterator ret = Search(interval_begin, lower, upper); |
| if (ret == DataEnd()) { |
| return ret; |
| } |
| // Update the |cached_index_| to point to the higher index. |
| if (!looking_below) { |
| cached_index_ = ret.index_; |
| } |
| return ret; |
| } |
| |
| template <class T, class C> |
| std::size_t QuicIntervalDeque<T, C>::Size() const { |
| return container_.size(); |
| } |
| |
| template <class T, class C> |
| bool QuicIntervalDeque<T, C>::Empty() const { |
| return container_.size() == 0; |
| } |
| |
| template <class T, class C> |
| template <class U> |
| void QuicIntervalDeque<T, C>::PushBackUniversal(U&& item) { |
| QuicInterval<std::size_t> interval = item.interval(); |
| // Adding an empty interval is a bug. |
| if (interval.Empty()) { |
| QUIC_BUG << "Trying to save empty interval to QuicCircularDeque."; |
| return; |
| } |
| container_.push_back(std::forward<U>(item)); |
| if (!cached_index_.has_value()) { |
| cached_index_ = container_.size() - 1; |
| } |
| } |
| |
| template <class T, class C> |
| typename QuicIntervalDeque<T, C>::Iterator QuicIntervalDeque<T, C>::Search( |
| const std::size_t interval_begin, |
| const std::size_t begin_index, |
| const std::size_t end_index) { |
| auto begin = container_.begin() + begin_index; |
| auto end = container_.begin() + end_index; |
| auto res = std::lower_bound(begin, end, interval_begin, IntervalCompare()); |
| // Just because we run |lower_bound| and it didn't return |container_.end()| |
| // doesn't mean we found our desired interval. |
| if (res != end && res->interval().Contains(interval_begin)) { |
| return Iterator(std::distance(begin, res) + begin_index, this); |
| } |
| return DataEnd(); |
| } |
| |
| } // namespace quic |
| |
| #endif // QUICHE_QUIC_CORE_QUIC_INTERVAL_DEQUE_H_ |