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// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_CONTAINERS_INTRUSIVE_HEAP_H_
#define BASE_CONTAINERS_INTRUSIVE_HEAP_H_
// Implements a standard max-heap, but with arbitrary element removal. To
// facilitate this, each element has associated with it a HeapHandle (an opaque
// wrapper around the index at which the element is stored), which is maintained
// by the heap as elements move within it.
//
// An IntrusiveHeap is implemented as a standard max-heap over a std::vector<T>,
// like std::make_heap. Insertion, removal and updating are amortized O(lg size)
// (occasional O(size) cost if a new vector allocation is required). Retrieving
// an element by handle is O(1). Looking up the top element is O(1). Insertions,
// removals and updates invalidate all iterators, but handles remain valid.
// Similar to a std::set, all iterators are read-only so as to disallow changing
// elements and violating the heap property. That being said, if the type you
// are storing is able to have its sort key be changed externally you can
// repair the heap by resorting the modified element via a call to "Update".
//
// Example usage:
//
// // Create a heap, wrapping integer elements with WithHeapHandle in order to
// // endow them with heap handles.
// IntrusiveHeap<WithHeapHandle<int>> heap;
//
// // WithHeapHandle<T> is for simple or opaque types. In cases where you
// // control the type declaration you can also provide HeapHandle storage by
// // deriving from InternalHeapHandleStorage.
// class Foo : public InternalHeapHandleStorage {
// public:
// explicit Foo(int);
// ...
// };
// IntrusiveHeap<Foo> heap2;
//
// // Insert some elements. Like most containers, "insert" returns an iterator
// // to the element in the container.
// heap.insert(3);
// heap.insert(1);
// auto it = heap.insert(4);
//
// // By default this is a max heap, so the top element should be 4 at this
// // point.
// EXPECT_EQ(4, heap.top().value());
//
// // Iterators are invalidated by further heap operations, but handles are
// // not. Grab a handle to the current top element so we can track it across
// // changes.
// HeapHandle* handle = it->handle();
//
// // Insert a new max element. 4 should no longer be the top.
// heap.insert(5);
// EXPECT_EQ(5, heap.top().value());
//
// // We can lookup and erase element 4 by its handle, even though it has
// // moved. Note that erasing the element invalidates the handle to it.
// EXPECT_EQ(4, heap.at(*handle).value());
// heap.erase(*handle);
// handle = nullptr;
//
// // Popping the current max (5), makes 3 the new max, as we already erased
// // element 4.
// heap.pop();
// EXPECT_EQ(3, heap.top().value());
//
// Under the hood the HeapHandle is managed by an object implementing the
// HeapHandleAccess interface, which is passed as a parameter to the
// IntrusiveHeap template:
//
// // Gets the heap handle associated with the element. This should return the
// // most recently set handle value, or HeapHandle::Invalid(). This is only
// // called in DCHECK builds.
// HeapHandle GetHeapHandle(const T*);
//
// // Changes the result of GetHeapHandle. GetHeapHandle() must return the
// // most recent value provided to SetHeapHandle() or HeapHandle::Invalid().
// // In some implementations, where GetHeapHandle() can independently
// // reproduce the correct value, it is possible that SetHeapHandle() does
// // nothing.
// void SetHeapHandle(T*, HeapHandle);
//
// // Clears the heap handle associated with the given element. After calling
// // this GetHeapHandle() must return HeapHandle::Invalid().
// void ClearHeapHandle(T*);
//
// The default implementation of HeapHandleAccess assumes that your type
// provides HeapHandle storage and will simply forward these calls to equivalent
// member functions on the type T:
//
// void T::SetHeapHandle(HeapHandle)
// void T::ClearHeapHandle()
// HeapHandle T::GetHeapHandle() const
//
// The WithHeapHandle and InternalHeapHandleStorage classes in turn provide
// implementations of that contract.
//
// In summary, to provide heap handle support for your type, you can do one of
// the following (from most manual / least magical, to least manual / most
// magical):
//
// 0. use a custom HeapHandleAccessor, and implement storage however you want;
// 1. use the default HeapHandleAccessor, and manually provide storage on your
// your element type and implement the IntrusiveHeap contract;
// 2. use the default HeapHandleAccessor, and endow your type with handle
// storage by deriving from a helper class (see InternalHeapHandleStorage);
// or,
// 3. use the default HeapHandleAccessor, and wrap your type in a container that
// provides handle storage (see WithHeapHandle<T>).
//
// Approach 0 is suitable for custom types that already implement something akin
// to heap handles, via back pointers or any other mechanism, but where the
// storage is external to the objects in the heap. If you already have the
// ability to determine where in a container an object lives despite it
// being moved, then you don't need the overhead of storing an actual HeapHandle
// whose value can be inferred.
//
// Approach 1 is is suitable in cases like the above, but where the data
// allowing you to determine the index of an element in a container is stored
// directly in the object itself.
//
// Approach 2 is suitable for types whose declarations you control, where you
// are able to use inheritance.
//
// Finally, approach 3 is suitable when you are storing PODs, or a type whose
// declaration you can not change.
//
// Most users should be using approach 2 or 3.
#include <algorithm>
#include <functional>
#include <limits>
#include <memory>
#include <type_traits>
#include <utility>
#include <vector>
#include "base/base_export.h"
#include "base/check.h"
#include "base/check_op.h"
#include "base/memory/ptr_util.h"
#include "base/ranges/algorithm.h"
#include "third_party/abseil-cpp/absl/container/inlined_vector.h"
namespace base {
// Intended as a wrapper around an |index_| in the vector storage backing an
// IntrusiveHeap. A HeapHandle is associated with each element in an
// IntrusiveHeap, and is maintained by the heap as the object moves around
// within it. It can be used to subsequently remove the element, or update it
// in place.
class BASE_EXPORT HeapHandle {
public:
enum : size_t { kInvalidIndex = std::numeric_limits<size_t>::max() };
constexpr HeapHandle() = default;
constexpr HeapHandle(const HeapHandle& other) = default;
HeapHandle(HeapHandle&& other) noexcept
: index_(std::exchange(other.index_, kInvalidIndex)) {}
~HeapHandle() = default;
HeapHandle& operator=(const HeapHandle& other) = default;
HeapHandle& operator=(HeapHandle&& other) noexcept {
index_ = std::exchange(other.index_, kInvalidIndex);
return *this;
}
static HeapHandle Invalid();
// Resets this handle back to an invalid state.
void reset() { index_ = kInvalidIndex; }
// Accessors.
size_t index() const { return index_; }
bool IsValid() const { return index_ != kInvalidIndex; }
// Comparison operators.
friend bool operator==(const HeapHandle& lhs, const HeapHandle& rhs) {
return lhs.index_ == rhs.index_;
}
friend bool operator!=(const HeapHandle& lhs, const HeapHandle& rhs) {
return lhs.index_ != rhs.index_;
}
friend bool operator<(const HeapHandle& lhs, const HeapHandle& rhs) {
return lhs.index_ < rhs.index_;
}
friend bool operator>(const HeapHandle& lhs, const HeapHandle& rhs) {
return lhs.index_ > rhs.index_;
}
friend bool operator<=(const HeapHandle& lhs, const HeapHandle& rhs) {
return lhs.index_ <= rhs.index_;
}
friend bool operator>=(const HeapHandle& lhs, const HeapHandle& rhs) {
return lhs.index_ >= rhs.index_;
}
private:
template <typename T, typename Compare, typename HeapHandleAccessor>
friend class IntrusiveHeap;
// Only IntrusiveHeaps can create valid HeapHandles.
explicit HeapHandle(size_t index) : index_(index) {}
size_t index_ = kInvalidIndex;
};
// The default HeapHandleAccessor, which simply forwards calls to the underlying
// type.
template <typename T>
struct DefaultHeapHandleAccessor {
void SetHeapHandle(T* element, HeapHandle handle) const {
element->SetHeapHandle(handle);
}
void ClearHeapHandle(T* element) const { element->ClearHeapHandle(); }
HeapHandle GetHeapHandle(const T* element) const {
return element->GetHeapHandle();
}
};
// Intrusive heap class. This is something like a std::vector (insertion and
// removal are similar, objects don't have a fixed address in memory) crossed
// with a std::set (elements are considered immutable once they're in the
// container).
template <typename T,
typename Compare = std::less<T>,
typename HeapHandleAccessor = DefaultHeapHandleAccessor<T>>
class IntrusiveHeap {
private:
using UnderlyingType = std::vector<T>;
public:
//////////////////////////////////////////////////////////////////////////////
// Types.
using value_type = typename UnderlyingType::value_type;
using size_type = typename UnderlyingType::size_type;
using difference_type = typename UnderlyingType::difference_type;
using value_compare = Compare;
using heap_handle_accessor = HeapHandleAccessor;
using reference = typename UnderlyingType::reference;
using const_reference = typename UnderlyingType::const_reference;
using pointer = typename UnderlyingType::pointer;
using const_pointer = typename UnderlyingType::const_pointer;
// Iterators are read-only.
using iterator = typename UnderlyingType::const_iterator;
using const_iterator = typename UnderlyingType::const_iterator;
using reverse_iterator = typename UnderlyingType::const_reverse_iterator;
using const_reverse_iterator =
typename UnderlyingType::const_reverse_iterator;
//////////////////////////////////////////////////////////////////////////////
// Lifetime.
IntrusiveHeap() = default;
IntrusiveHeap(const value_compare& comp, const heap_handle_accessor& access)
: impl_(comp, access) {}
template <class InputIterator>
IntrusiveHeap(InputIterator first,
InputIterator last,
const value_compare& comp = value_compare(),
const heap_handle_accessor& access = heap_handle_accessor())
: impl_(comp, access) {
insert(first, last);
}
// Moves an intrusive heap. The outstanding handles remain valid and end up
// pointing to the new heap.
IntrusiveHeap(IntrusiveHeap&& other) = default;
// Copy constructor for an intrusive heap.
IntrusiveHeap(const IntrusiveHeap&);
// Initializer list constructor.
template <typename U>
IntrusiveHeap(std::initializer_list<U> ilist,
const value_compare& comp = value_compare(),
const heap_handle_accessor& access = heap_handle_accessor())
: impl_(comp, access) {
insert(std::begin(ilist), std::end(ilist));
}
~IntrusiveHeap();
//////////////////////////////////////////////////////////////////////////////
// Assignment.
IntrusiveHeap& operator=(IntrusiveHeap&&) noexcept;
IntrusiveHeap& operator=(const IntrusiveHeap&);
IntrusiveHeap& operator=(std::initializer_list<value_type> ilist);
//////////////////////////////////////////////////////////////////////////////
// Element access.
//
// These provide O(1) const access to the elements in the heap. If you wish to
// modify an element in the heap you should first remove it from the heap, and
// then reinsert it into the heap, or use the "Replace*" helper functions. In
// the rare case where you directly modify an element in the heap you can
// subsequently repair the heap with "Update".
const_reference at(size_type pos) const { return impl_.heap_.at(pos); }
const_reference at(HeapHandle pos) const {
return impl_.heap_.at(pos.index());
}
const_reference operator[](size_type pos) const { return impl_.heap_[pos]; }
const_reference operator[](HeapHandle pos) const {
return impl_.heap_[pos.index()];
}
const_reference front() const { return impl_.heap_.front(); }
const_reference back() const { return impl_.heap_.back(); }
const_reference top() const { return impl_.heap_.front(); }
// May or may not return a null pointer if size() is zero.
const_pointer data() const { return impl_.heap_.data(); }
//////////////////////////////////////////////////////////////////////////////
// Memory management.
void reserve(size_type new_capacity) { impl_.heap_.reserve(new_capacity); }
size_type capacity() const { return impl_.heap_.capacity(); }
void shrink_to_fit() { impl_.heap_.shrink_to_fit(); }
//////////////////////////////////////////////////////////////////////////////
// Size management.
void clear();
size_type size() const { return impl_.heap_.size(); }
size_type max_size() const { return impl_.heap_.max_size(); }
bool empty() const { return impl_.heap_.empty(); }
//////////////////////////////////////////////////////////////////////////////
// Iterators.
//
// Only constant iterators are allowed.
const_iterator begin() const { return impl_.heap_.cbegin(); }
const_iterator cbegin() const { return impl_.heap_.cbegin(); }
const_iterator end() const { return impl_.heap_.cend(); }
const_iterator cend() const { return impl_.heap_.cend(); }
const_reverse_iterator rbegin() const { return impl_.heap_.crbegin(); }
const_reverse_iterator crbegin() const { return impl_.heap_.crbegin(); }
const_reverse_iterator rend() const { return impl_.heap_.crend(); }
const_reverse_iterator crend() const { return impl_.heap_.crend(); }
//////////////////////////////////////////////////////////////////////////////
// Insertion (these are std::multiset like, with no position hints).
//
// All insertion operations invalidate iterators, pointers and references.
// Handles remain valid. Insertion of one element is amortized O(lg size)
// (occasional O(size) cost if a new vector allocation is required).
const_iterator insert(const value_type& value) { return InsertImpl(value); }
const_iterator insert(value_type&& value) {
return InsertImpl(std::move_if_noexcept(value));
}
template <class InputIterator>
void insert(InputIterator first, InputIterator last);
template <typename... Args>
const_iterator emplace(Args&&... args);
//////////////////////////////////////////////////////////////////////////////
// Removing elements.
//
// Erasing invalidates all outstanding iterators, pointers and references.
// Handles remain valid. Removing one element is amortized O(lg size)
// (occasional O(size) cost if a new vector allocation is required).
//
// Note that it is safe for the element being removed to be in an invalid
// state (modified such that it may currently violate the heap property)
// when this called.
// Takes the element from the heap at the given position, erasing that entry
// from the heap. This can only be called if |value_type| is movable.
value_type take(size_type pos);
// Version of take that will accept iterators and handles. This can only be
// called if |value_type| is movable.
template <typename P>
value_type take(P pos) {
return take(ToIndex(pos));
}
// Takes the top element from the heap.
value_type take_top() { return take(0u); }
// Erases the element at the given position |pos|.
void erase(size_type pos);
// Version of erase that will accept iterators and handles.
template <typename P>
void erase(P pos) {
erase(ToIndex(pos));
}
// Removes the element at the top of the heap (accessible via "top", or
// "front" or "take").
void pop() { erase(0u); }
// Erases every element that matches the predicate. This is done in-place for
// maximum efficiency. Also, to avoid re-entrancy issues, elements are deleted
// at the very end.
// Note: This function is currently tuned for a use-case where there are
// usually 8 or less elements removed at a time. Consider adding a template
// parameter if a different tuning is needed.
template <typename Functor>
void EraseIf(Functor predicate) {
// Stable partition ensures that if no elements are erased, the heap remains
// intact.
auto erase_start = std::stable_partition(
impl_.heap_.begin(), impl_.heap_.end(),
[&](const auto& element) { return !predicate(element); });
// Clear the heap handle of every element that will be erased.
for (size_t i = static_cast<size_t>(erase_start - impl_.heap_.begin());
i < impl_.heap_.size(); ++i) {
ClearHeapHandle(i);
}
// Deleting an element can potentially lead to reentrancy, we move all the
// elements to be erased into a temporary container before deleting them.
// This is to avoid changing the underlying container during the erase()
// call.
absl::InlinedVector<value_type, 8> elements_to_delete;
std::move(erase_start, impl_.heap_.end(),
std::back_inserter(elements_to_delete));
impl_.heap_.erase(erase_start, impl_.heap_.end());
// If no elements were removed, then the heap is still intact.
if (elements_to_delete.empty()) {
return;
}
// Repair the heap and ensure handles are pointing to the right index.
ranges::make_heap(impl_.heap_, value_comp());
for (size_t i = 0; i < size(); ++i)
SetHeapHandle(i);
// Explicitly delete elements last.
elements_to_delete.clear();
}
//////////////////////////////////////////////////////////////////////////////
// Updating.
//
// Amortized cost of O(lg size).
// Replaces the element corresponding to |handle| with a new |element|.
const_iterator Replace(size_type pos, const T& element) {
return ReplaceImpl(pos, element);
}
const_iterator Replace(size_type pos, T&& element) {
return ReplaceImpl(pos, std::move_if_noexcept(element));
}
// Versions of Replace that will accept handles and iterators.
template <typename P>
const_iterator Replace(P pos, const T& element) {
return ReplaceImpl(ToIndex(pos), element);
}
template <typename P>
const_iterator Replace(P pos, T&& element) {
return ReplaceImpl(ToIndex(pos), std::move_if_noexcept(element));
}
// Replaces the top element in the heap with the provided element.
const_iterator ReplaceTop(const T& element) {
return ReplaceTopImpl(element);
}
const_iterator ReplaceTop(T&& element) {
return ReplaceTopImpl(std::move_if_noexcept(element));
}
// Causes the object at the given location to be resorted into an appropriate
// position in the heap. To be used if the object in the heap was externally
// modified, and the heap needs to be repaired. This only works if a single
// heap element has been modified, otherwise the behaviour is undefined.
const_iterator Update(size_type pos);
template <typename P>
const_iterator Update(P pos) {
return Update(ToIndex(pos));
}
// Applies a modification function to the object at the given location, then
// repairs the heap. To be used to modify an element in the heap in-place
// while keeping the heap intact.
template <typename P, typename UnaryOperation>
const_iterator Modify(P pos, UnaryOperation unary_op) {
size_type index = ToIndex(pos);
unary_op(impl_.heap_.at(index));
return Update(index);
}
//////////////////////////////////////////////////////////////////////////////
// Access to helper functors.
const value_compare& value_comp() const { return impl_.get_value_compare(); }
const heap_handle_accessor& heap_handle_access() const {
return impl_.get_heap_handle_access();
}
//////////////////////////////////////////////////////////////////////////////
// General operations.
void swap(IntrusiveHeap& other) noexcept;
friend void swap(IntrusiveHeap& lhs, IntrusiveHeap& rhs) { lhs.swap(rhs); }
// Comparison operators. These check for exact equality. Two heaps that are
// semantically equivalent (contain the same elements, but in different
// orders) won't compare as equal using these operators.
friend bool operator==(const IntrusiveHeap& lhs, const IntrusiveHeap& rhs) {
return lhs.impl_.heap_ == rhs.impl_.heap_;
}
friend bool operator!=(const IntrusiveHeap& lhs, const IntrusiveHeap& rhs) {
return lhs.impl_.heap_ != rhs.impl_.heap_;
}
//////////////////////////////////////////////////////////////////////////////
// Utility functions.
// Converts iterators and handles to indices. Helpers for templated versions
// of insert/erase/Replace.
size_type ToIndex(HeapHandle handle) { return handle.index(); }
size_type ToIndex(const_iterator pos);
size_type ToIndex(const_reverse_iterator pos);
private:
// Templated version of ToIndex that lets insert/erase/Replace work with all
// integral types.
template <typename I, typename = std::enable_if_t<std::is_integral_v<I>>>
size_type ToIndex(I pos) {
return static_cast<size_type>(pos);
}
// Returns the last valid index in |heap_|.
size_type GetLastIndex() const { return impl_.heap_.size() - 1; }
// Helper functions for setting heap handles.
void SetHeapHandle(size_type i);
void ClearHeapHandle(size_type i);
HeapHandle GetHeapHandle(size_type i);
// Helpers for doing comparisons between elements inside and outside of the
// heap.
bool Less(size_type i, size_type j);
bool Less(const T& element, size_type i);
bool Less(size_type i, const T& element);
// The following function are all related to the basic heap algorithm
// underpinning this data structure. They are templated so that they work with
// both movable (U = T&&) and non-movable (U = const T&) types.
// Primitive helpers for adding removing / elements to the heap. To minimize
// moves, the heap is implemented by making a hole where an element used to
// be (or where a new element will soon be), and moving the hole around,
// before finally filling the hole or deleting the entry corresponding to the
// hole.
void MakeHole(size_type pos);
template <typename U>
void FillHole(size_type hole, U element);
void MoveHole(size_type new_hole_pos, size_type old_hole_pos);
// Moves a hold up the tree and fills it with the provided |element|. Returns
// the final index of the element.
template <typename U>
size_type MoveHoleUpAndFill(size_type hole_pos, U element);
// Moves a hole down the tree and fills it with the provided |element|. If
// |kFillWithLeaf| is true it will deterministically move the hole all the
// way down the tree, avoiding a second comparison per level, before
// potentially moving it back up the tree.
struct WithLeafElement {
static constexpr bool kIsLeafElement = true;
};
struct WithElement {
static constexpr bool kIsLeafElement = false;
};
template <typename FillElementType, typename U>
size_type MoveHoleDownAndFill(size_type hole_pos, U element);
// Implementation of Insert and Replace built on top of the MoveHole
// primitives.
template <typename U>
const_iterator InsertImpl(U element);
template <typename U>
const_iterator ReplaceImpl(size_type pos, U element);
template <typename U>
const_iterator ReplaceTopImpl(U element);
// To support comparators that may not be possible to default-construct, we
// have to store an instance of value_compare. Using this to store all
// internal state of IntrusiveHeap and using private inheritance to store
// compare lets us take advantage of an empty base class optimization to avoid
// extra space in the common case when Compare has no state.
struct Impl : private value_compare, private heap_handle_accessor {
Impl(const value_compare& value_comp,
const heap_handle_accessor& heap_handle_access)
: value_compare(value_comp), heap_handle_accessor(heap_handle_access) {}
Impl() = default;
Impl(Impl&&) = default;
Impl(const Impl&) = default;
Impl& operator=(Impl&& other) = default;
Impl& operator=(const Impl& other) = default;
const value_compare& get_value_compare() const { return *this; }
value_compare& get_value_compare() { return *this; }
const heap_handle_accessor& get_heap_handle_access() const { return *this; }
heap_handle_accessor& get_heap_handle_access() { return *this; }
// The items in the heap.
UnderlyingType heap_;
} impl_;
};
// Helper class to endow an object with internal HeapHandle storage. By deriving
// from this type you endow your class with self-owned storage for a HeapHandle.
// This is a move-only type so that the handle follows the element across moves
// and resizes of the underlying vector.
class BASE_EXPORT InternalHeapHandleStorage {
public:
InternalHeapHandleStorage();
InternalHeapHandleStorage(const InternalHeapHandleStorage&) = delete;
InternalHeapHandleStorage(InternalHeapHandleStorage&& other) noexcept;
virtual ~InternalHeapHandleStorage();
InternalHeapHandleStorage& operator=(const InternalHeapHandleStorage&) =
delete;
InternalHeapHandleStorage& operator=(
InternalHeapHandleStorage&& other) noexcept;
// Allows external clients to get a pointer to the heap handle. This allows
// them to remove the element from the heap regardless of its location.
HeapHandle* handle() const { return handle_.get(); }
// Implementation of IntrusiveHeap contract. Inlined to keep heap code as fast
// as possible.
void SetHeapHandle(HeapHandle handle) {
DCHECK(handle.IsValid());
if (handle_)
*handle_ = handle;
}
void ClearHeapHandle() {
if (handle_)
handle_->reset();
}
HeapHandle GetHeapHandle() const {
if (handle_)
return *handle_;
return HeapHandle::Invalid();
}
// Utility functions.
void swap(InternalHeapHandleStorage& other) noexcept;
friend void swap(InternalHeapHandleStorage& lhs,
InternalHeapHandleStorage& rhs) {
lhs.swap(rhs);
}
private:
std::unique_ptr<HeapHandle> handle_;
};
// Spiritually akin to a std::pair<T, std::unique_ptr<HeapHandle>>. Can be used
// to wrap arbitrary types and provide them with a HeapHandle, making them
// appropriate for use in an IntrusiveHeap. This is a move-only type.
template <typename T>
class WithHeapHandle : public InternalHeapHandleStorage {
public:
WithHeapHandle() = default;
// Allow implicit conversion of any type that T supports for ease of use with
// InstrusiveHeap constructors/insert/emplace.
template <typename U>
WithHeapHandle(U value) : value_(std::move_if_noexcept(value)) {}
WithHeapHandle(T&& value) noexcept : value_(std::move(value)) {}
// Constructor that forwards all arguments along to |value_|.
template <class... Args>
explicit WithHeapHandle(Args&&... args);
WithHeapHandle(const WithHeapHandle&) = delete;
WithHeapHandle(WithHeapHandle&& other) noexcept = default;
~WithHeapHandle() override = default;
WithHeapHandle& operator=(const WithHeapHandle&) = delete;
WithHeapHandle& operator=(WithHeapHandle&& other) = default;
T& value() { return value_; }
const T& value() const { return value_; }
// Utility functions.
void swap(WithHeapHandle& other) noexcept;
friend void swap(WithHeapHandle& lhs, WithHeapHandle& rhs) { lhs.swap(rhs); }
// Comparison operators, for compatibility with ordered STL containers.
friend bool operator==(const WithHeapHandle& lhs, const WithHeapHandle& rhs) {
return lhs.value_ == rhs.value_;
}
friend bool operator!=(const WithHeapHandle& lhs, const WithHeapHandle& rhs) {
return lhs.value_ != rhs.value_;
}
friend bool operator<=(const WithHeapHandle& lhs, const WithHeapHandle& rhs) {
return lhs.value_ <= rhs.value_;
}
friend bool operator<(const WithHeapHandle& lhs, const WithHeapHandle& rhs) {
return lhs.value_ < rhs.value_;
}
friend bool operator>=(const WithHeapHandle& lhs, const WithHeapHandle& rhs) {
return lhs.value_ >= rhs.value_;
}
friend bool operator>(const WithHeapHandle& lhs, const WithHeapHandle& rhs) {
return lhs.value_ > rhs.value_;
}
private:
T value_;
};
////////////////////////////////////////////////////////////////////////////////
// IMPLEMENTATION DETAILS
namespace intrusive_heap {
BASE_EXPORT inline size_t ParentIndex(size_t i) {
DCHECK_NE(0u, i);
return (i - 1) / 2;
}
BASE_EXPORT inline size_t LeftIndex(size_t i) {
return 2 * i + 1;
}
template <typename HandleType>
bool IsInvalid(const HandleType& handle) {
return !handle || !handle->IsValid();
}
BASE_EXPORT inline void CheckInvalidOrEqualTo(HeapHandle handle, size_t index) {
if (handle.IsValid())
DCHECK_EQ(index, handle.index());
}
} // namespace intrusive_heap
////////////////////////////////////////////////////////////////////////////////
// IntrusiveHeap
template <typename T, typename Compare, typename HeapHandleAccessor>
IntrusiveHeap<T, Compare, HeapHandleAccessor>::IntrusiveHeap(
const IntrusiveHeap& other)
: impl_(other.impl_) {
for (size_t i = 0; i < size(); ++i) {
SetHeapHandle(i);
}
}
template <typename T, typename Compare, typename HeapHandleAccessor>
IntrusiveHeap<T, Compare, HeapHandleAccessor>::~IntrusiveHeap() {
clear();
}
template <typename T, typename Compare, typename HeapHandleAccessor>
IntrusiveHeap<T, Compare, HeapHandleAccessor>&
IntrusiveHeap<T, Compare, HeapHandleAccessor>::operator=(
IntrusiveHeap&& other) noexcept {
clear();
impl_ = std::move(other.impl_);
return *this;
}
template <typename T, typename Compare, typename HeapHandleAccessor>
IntrusiveHeap<T, Compare, HeapHandleAccessor>&
IntrusiveHeap<T, Compare, HeapHandleAccessor>::operator=(
const IntrusiveHeap& other) {
clear();
impl_ = other.impl_;
for (size_t i = 0; i < size(); ++i) {
SetHeapHandle(i);
}
return *this;
}
template <typename T, typename Compare, typename HeapHandleAccessor>
IntrusiveHeap<T, Compare, HeapHandleAccessor>&
IntrusiveHeap<T, Compare, HeapHandleAccessor>::operator=(
std::initializer_list<value_type> ilist) {
clear();
insert(std::begin(ilist), std::end(ilist));
}
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::clear() {
// Make all of the handles invalid before cleaning up the heap.
for (size_type i = 0; i < size(); ++i) {
ClearHeapHandle(i);
}
// Clear the heap.
impl_.heap_.clear();
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <class InputIterator>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::insert(InputIterator first,
InputIterator last) {
for (auto it = first; it != last; ++it) {
insert(value_type(*it));
}
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename... Args>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::const_iterator
IntrusiveHeap<T, Compare, HeapHandleAccessor>::emplace(Args&&... args) {
value_type value(std::forward<Args>(args)...);
return InsertImpl(std::move_if_noexcept(value));
}
template <typename T, typename Compare, typename HeapHandleAccessor>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::value_type
IntrusiveHeap<T, Compare, HeapHandleAccessor>::take(size_type pos) {
// Make a hole by taking the element out of the heap.
MakeHole(pos);
value_type val = std::move(impl_.heap_[pos]);
// If the element being taken is already the last element then the heap
// doesn't need to be repaired.
if (pos != GetLastIndex()) {
MakeHole(GetLastIndex());
// Move the hole down the heap, filling it with the current leaf at the
// very end of the heap.
MoveHoleDownAndFill<WithLeafElement>(
pos, std::move(impl_.heap_[GetLastIndex()]));
}
impl_.heap_.pop_back();
return val;
}
// This is effectively identical to "take", but it avoids an unnecessary move.
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::erase(size_type pos) {
DCHECK_LT(pos, size());
// Make a hole by taking the element out of the heap.
MakeHole(pos);
// If the element being erased is already the last element then the heap
// doesn't need to be repaired.
if (pos != GetLastIndex()) {
MakeHole(GetLastIndex());
// Move the hole down the heap, filling it with the current leaf at the
// very end of the heap.
MoveHoleDownAndFill<WithLeafElement>(
pos, std::move_if_noexcept(impl_.heap_[GetLastIndex()]));
}
impl_.heap_.pop_back();
}
template <typename T, typename Compare, typename HeapHandleAccessor>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::const_iterator
IntrusiveHeap<T, Compare, HeapHandleAccessor>::Update(size_type pos) {
DCHECK_LT(pos, size());
MakeHole(pos);
// Determine if we're >= parent, in which case we may need to go up.
bool child_greater_eq_parent = false;
size_type i = 0;
if (pos > 0) {
i = intrusive_heap::ParentIndex(pos);
child_greater_eq_parent = !Less(pos, i);
}
if (child_greater_eq_parent) {
i = MoveHoleUpAndFill(pos, std::move_if_noexcept(impl_.heap_[pos]));
} else {
i = MoveHoleDownAndFill<WithElement>(
pos, std::move_if_noexcept(impl_.heap_[pos]));
}
return cbegin() + i;
}
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::swap(
IntrusiveHeap& other) noexcept {
std::swap(impl_.get_value_compare(), other.impl_.get_value_compare());
std::swap(impl_.get_heap_handle_access(),
other.impl_.get_heap_handle_access());
std::swap(impl_.heap_, other.impl_.heap_);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::size_type
IntrusiveHeap<T, Compare, HeapHandleAccessor>::ToIndex(const_iterator pos) {
DCHECK(cbegin() <= pos);
DCHECK(pos <= cend());
if (pos == cend())
return HeapHandle::kInvalidIndex;
return pos - cbegin();
}
template <typename T, typename Compare, typename HeapHandleAccessor>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::size_type
IntrusiveHeap<T, Compare, HeapHandleAccessor>::ToIndex(
const_reverse_iterator pos) {
DCHECK(crbegin() <= pos);
DCHECK(pos <= crend());
if (pos == crend())
return HeapHandle::kInvalidIndex;
return (pos.base() - cbegin()) - 1;
}
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::SetHeapHandle(size_type i) {
impl_.get_heap_handle_access().SetHeapHandle(&impl_.heap_[i], HeapHandle(i));
intrusive_heap::CheckInvalidOrEqualTo(GetHeapHandle(i), i);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::ClearHeapHandle(
size_type i) {
impl_.get_heap_handle_access().ClearHeapHandle(&impl_.heap_[i]);
DCHECK(!GetHeapHandle(i).IsValid());
}
template <typename T, typename Compare, typename HeapHandleAccessor>
HeapHandle IntrusiveHeap<T, Compare, HeapHandleAccessor>::GetHeapHandle(
size_type i) {
return impl_.get_heap_handle_access().GetHeapHandle(&impl_.heap_[i]);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
bool IntrusiveHeap<T, Compare, HeapHandleAccessor>::Less(size_type i,
size_type j) {
DCHECK_LT(i, size());
DCHECK_LT(j, size());
return impl_.get_value_compare()(impl_.heap_[i], impl_.heap_[j]);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
bool IntrusiveHeap<T, Compare, HeapHandleAccessor>::Less(const T& element,
size_type i) {
DCHECK_LT(i, size());
return impl_.get_value_compare()(element, impl_.heap_[i]);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
bool IntrusiveHeap<T, Compare, HeapHandleAccessor>::Less(size_type i,
const T& element) {
DCHECK_LT(i, size());
return impl_.get_value_compare()(impl_.heap_[i], element);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::MakeHole(size_type pos) {
DCHECK_LT(pos, size());
ClearHeapHandle(pos);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename U>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::FillHole(size_type hole_pos,
U element) {
// The hole that we're filling may not yet exist. This can occur when
// inserting a new element into the heap.
DCHECK_LE(hole_pos, size());
if (hole_pos == size()) {
impl_.heap_.push_back(std::move_if_noexcept(element));
} else {
impl_.heap_[hole_pos] = std::move_if_noexcept(element);
}
SetHeapHandle(hole_pos);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
void IntrusiveHeap<T, Compare, HeapHandleAccessor>::MoveHole(
size_type new_hole_pos,
size_type old_hole_pos) {
// The old hole position may be one past the end. This occurs when a new
// element is being added.
DCHECK_NE(new_hole_pos, old_hole_pos);
DCHECK_LT(new_hole_pos, size());
DCHECK_LE(old_hole_pos, size());
if (old_hole_pos == size()) {
impl_.heap_.push_back(std::move_if_noexcept(impl_.heap_[new_hole_pos]));
} else {
impl_.heap_[old_hole_pos] =
std::move_if_noexcept(impl_.heap_[new_hole_pos]);
}
SetHeapHandle(old_hole_pos);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename U>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::size_type
IntrusiveHeap<T, Compare, HeapHandleAccessor>::MoveHoleUpAndFill(
size_type hole_pos,
U element) {
// Moving 1 spot beyond the end is fine. This happens when we insert a new
// element.
DCHECK_LE(hole_pos, size());
// Stop when the element is as far up as it can go.
while (hole_pos != 0) {
// If our parent is >= to us, we can stop.
size_type parent = intrusive_heap::ParentIndex(hole_pos);
if (!Less(parent, element))
break;
MoveHole(parent, hole_pos);
hole_pos = parent;
}
FillHole(hole_pos, std::move_if_noexcept(element));
return hole_pos;
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename FillElementType, typename U>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::size_type
IntrusiveHeap<T, Compare, HeapHandleAccessor>::MoveHoleDownAndFill(
size_type hole_pos,
U element) {
DCHECK_LT(hole_pos, size());
// If we're filling with a leaf, then that leaf element is about to be erased.
// We pretend that the space doesn't exist in the heap.
const size_type n = size() - (FillElementType::kIsLeafElement ? 1 : 0);
DCHECK_LT(hole_pos, n);
DCHECK(!GetHeapHandle(hole_pos).IsValid());
while (true) {
// If this spot has no children, then we've gone down as far as we can go.
size_type left = intrusive_heap::LeftIndex(hole_pos);
if (left >= n)
break;
size_type right = left + 1;
// Get the larger of the potentially two child nodes.
size_type largest = left;
if (right < n && Less(left, right))
largest = right;
// If we're not deterministically moving the element all the way down to
// become a leaf, then stop when it is >= the largest of the children.
if (!FillElementType::kIsLeafElement && !Less(element, largest))
break;
MoveHole(largest, hole_pos);
hole_pos = largest;
}
if (FillElementType::kIsLeafElement) {
// If we're filling with a leaf node we may need to bubble the leaf back up
// the tree a bit to repair the heap.
hole_pos = MoveHoleUpAndFill(hole_pos, std::move_if_noexcept(element));
} else {
FillHole(hole_pos, std::move_if_noexcept(element));
}
return hole_pos;
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename U>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::const_iterator
IntrusiveHeap<T, Compare, HeapHandleAccessor>::InsertImpl(U element) {
// MoveHoleUpAndFill can tolerate the initial hole being in a slot that
// doesn't yet exist. It will be created by MoveHole by copy/move, thus
// removing the need for a default constructor.
size_type i = MoveHoleUpAndFill(size(), std::move_if_noexcept(element));
return cbegin() + static_cast<difference_type>(i);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename U>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::const_iterator
IntrusiveHeap<T, Compare, HeapHandleAccessor>::ReplaceImpl(size_type pos,
U element) {
// If we're greater than our parent we need to go up, otherwise we may need
// to go down.
MakeHole(pos);
size_type i = 0;
if (!Less(element, pos)) {
i = MoveHoleUpAndFill(pos, std::move_if_noexcept(element));
} else {
i = MoveHoleDownAndFill<WithElement>(pos, std::move_if_noexcept(element));
}
return cbegin() + static_cast<difference_type>(i);
}
template <typename T, typename Compare, typename HeapHandleAccessor>
template <typename U>
typename IntrusiveHeap<T, Compare, HeapHandleAccessor>::const_iterator
IntrusiveHeap<T, Compare, HeapHandleAccessor>::ReplaceTopImpl(U element) {
MakeHole(0u);
size_type i =
MoveHoleDownAndFill<WithElement>(0u, std::move_if_noexcept(element));
return cbegin() + static_cast<difference_type>(i);
}
////////////////////////////////////////////////////////////////////////////////
// WithHeapHandle
template <typename T>
template <class... Args>
WithHeapHandle<T>::WithHeapHandle(Args&&... args)
: value_(std::forward<Args>(args)...) {}
template <typename T>
void WithHeapHandle<T>::swap(WithHeapHandle& other) noexcept {
InternalHeapHandleStorage::swap(other);
std::swap(value_, other.value_);
}
} // namespace base
#endif // BASE_CONTAINERS_INTRUSIVE_HEAP_H_
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