| /* |
| * Copyright (C) 2014 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| #ifndef ART_RUNTIME_BASE_HASH_SET_H_ |
| #define ART_RUNTIME_BASE_HASH_SET_H_ |
| |
| #include <functional> |
| #include <memory> |
| #include <stdint.h> |
| #include <utility> |
| |
| #include "logging.h" |
| |
| namespace art { |
| |
| // Returns true if an item is empty. |
| template <class T> |
| class DefaultEmptyFn { |
| public: |
| void MakeEmpty(T& item) const { |
| item = T(); |
| } |
| bool IsEmpty(const T& item) const { |
| return item == T(); |
| } |
| }; |
| |
| template <class T> |
| class DefaultEmptyFn<T*> { |
| public: |
| void MakeEmpty(T*& item) const { |
| item = nullptr; |
| } |
| bool IsEmpty(const T*& item) const { |
| return item == nullptr; |
| } |
| }; |
| |
| // Low memory version of a hash set, uses less memory than std::unordered_set since elements aren't |
| // boxed. Uses linear probing. |
| // EmptyFn needs to implement two functions MakeEmpty(T& item) and IsEmpty(const T& item) |
| template <class T, class EmptyFn = DefaultEmptyFn<T>, class HashFn = std::hash<T>, |
| class Pred = std::equal_to<T>, class Alloc = std::allocator<T>> |
| class HashSet { |
| public: |
| static constexpr double kDefaultMinLoadFactor = 0.5; |
| static constexpr double kDefaultMaxLoadFactor = 0.9; |
| static constexpr size_t kMinBuckets = 1000; |
| |
| class Iterator { |
| public: |
| Iterator(const Iterator&) = default; |
| Iterator(HashSet* hash_set, size_t index) : hash_set_(hash_set), index_(index) { |
| } |
| Iterator& operator=(const Iterator&) = default; |
| bool operator==(const Iterator& other) const { |
| return hash_set_ == other.hash_set_ && index_ == other.index_; |
| } |
| bool operator!=(const Iterator& other) const { |
| return !(*this == other); |
| } |
| Iterator operator++() { // Value after modification. |
| index_ = NextNonEmptySlot(index_); |
| return *this; |
| } |
| Iterator operator++(int) { |
| Iterator temp = *this; |
| index_ = NextNonEmptySlot(index_); |
| return temp; |
| } |
| T& operator*() { |
| DCHECK(!hash_set_->IsFreeSlot(GetIndex())); |
| return hash_set_->ElementForIndex(index_); |
| } |
| const T& operator*() const { |
| DCHECK(!hash_set_->IsFreeSlot(GetIndex())); |
| return hash_set_->ElementForIndex(index_); |
| } |
| T* operator->() { |
| return &**this; |
| } |
| const T* operator->() const { |
| return &**this; |
| } |
| // TODO: Operator -- --(int) |
| |
| private: |
| HashSet* hash_set_; |
| size_t index_; |
| |
| size_t GetIndex() const { |
| return index_; |
| } |
| size_t NextNonEmptySlot(size_t index) const { |
| const size_t num_buckets = hash_set_->NumBuckets(); |
| DCHECK_LT(index, num_buckets); |
| do { |
| ++index; |
| } while (index < num_buckets && hash_set_->IsFreeSlot(index)); |
| return index; |
| } |
| |
| friend class HashSet; |
| }; |
| |
| void Clear() { |
| DeallocateStorage(); |
| AllocateStorage(1); |
| num_elements_ = 0; |
| elements_until_expand_ = 0; |
| } |
| HashSet() : num_elements_(0), num_buckets_(0), data_(nullptr), |
| min_load_factor_(kDefaultMinLoadFactor), max_load_factor_(kDefaultMaxLoadFactor) { |
| Clear(); |
| } |
| HashSet(const HashSet& other) : num_elements_(0), num_buckets_(0), data_(nullptr) { |
| *this = other; |
| } |
| HashSet(HashSet&& other) : num_elements_(0), num_buckets_(0), data_(nullptr) { |
| *this = std::move(other); |
| } |
| ~HashSet() { |
| DeallocateStorage(); |
| } |
| HashSet& operator=(HashSet&& other) { |
| std::swap(data_, other.data_); |
| std::swap(num_buckets_, other.num_buckets_); |
| std::swap(num_elements_, other.num_elements_); |
| std::swap(elements_until_expand_, other.elements_until_expand_); |
| std::swap(min_load_factor_, other.min_load_factor_); |
| std::swap(max_load_factor_, other.max_load_factor_); |
| return *this; |
| } |
| HashSet& operator=(const HashSet& other) { |
| DeallocateStorage(); |
| AllocateStorage(other.NumBuckets()); |
| for (size_t i = 0; i < num_buckets_; ++i) { |
| ElementForIndex(i) = other.data_[i]; |
| } |
| num_elements_ = other.num_elements_; |
| elements_until_expand_ = other.elements_until_expand_; |
| min_load_factor_ = other.min_load_factor_; |
| max_load_factor_ = other.max_load_factor_; |
| return *this; |
| } |
| // Lower case for c++11 for each. |
| Iterator begin() { |
| Iterator ret(this, 0); |
| if (num_buckets_ != 0 && IsFreeSlot(ret.GetIndex())) { |
| ++ret; // Skip all the empty slots. |
| } |
| return ret; |
| } |
| // Lower case for c++11 for each. |
| Iterator end() { |
| return Iterator(this, NumBuckets()); |
| } |
| bool Empty() { |
| return begin() == end(); |
| } |
| // Erase algorithm: |
| // Make an empty slot where the iterator is pointing. |
| // Scan fowards until we hit another empty slot. |
| // If an element inbetween doesn't rehash to the range from the current empty slot to the |
| // iterator. It must be before the empty slot, in that case we can move it to the empty slot |
| // and set the empty slot to be the location we just moved from. |
| // Relies on maintaining the invariant that there's no empty slots from the 'ideal' index of an |
| // element to its actual location/index. |
| Iterator Erase(Iterator it) { |
| // empty_index is the index that will become empty. |
| size_t empty_index = it.GetIndex(); |
| DCHECK(!IsFreeSlot(empty_index)); |
| size_t next_index = empty_index; |
| bool filled = false; // True if we filled the empty index. |
| while (true) { |
| next_index = NextIndex(next_index); |
| T& next_element = ElementForIndex(next_index); |
| // If the next element is empty, we are done. Make sure to clear the current empty index. |
| if (emptyfn_.IsEmpty(next_element)) { |
| emptyfn_.MakeEmpty(ElementForIndex(empty_index)); |
| break; |
| } |
| // Otherwise try to see if the next element can fill the current empty index. |
| const size_t next_hash = hashfn_(next_element); |
| // Calculate the ideal index, if it is within empty_index + 1 to next_index then there is |
| // nothing we can do. |
| size_t next_ideal_index = IndexForHash(next_hash); |
| // Loop around if needed for our check. |
| size_t unwrapped_next_index = next_index; |
| if (unwrapped_next_index < empty_index) { |
| unwrapped_next_index += NumBuckets(); |
| } |
| // Loop around if needed for our check. |
| size_t unwrapped_next_ideal_index = next_ideal_index; |
| if (unwrapped_next_ideal_index < empty_index) { |
| unwrapped_next_ideal_index += NumBuckets(); |
| } |
| if (unwrapped_next_ideal_index <= empty_index || |
| unwrapped_next_ideal_index > unwrapped_next_index) { |
| // If the target index isn't within our current range it must have been probed from before |
| // the empty index. |
| ElementForIndex(empty_index) = std::move(next_element); |
| filled = true; // TODO: Optimize |
| empty_index = next_index; |
| } |
| } |
| --num_elements_; |
| // If we didn't fill the slot then we need go to the next non free slot. |
| if (!filled) { |
| ++it; |
| } |
| return it; |
| } |
| // Find an element, returns end() if not found. |
| // Allows custom K types, example of when this is useful. |
| // Set of Class* sorted by name, want to find a class with a name but can't allocate a dummy |
| // object in the heap for performance solution. |
| template <typename K> |
| Iterator Find(const K& element) { |
| return FindWithHash(element, hashfn_(element)); |
| } |
| template <typename K> |
| Iterator FindWithHash(const K& element, size_t hash) { |
| DCHECK_EQ(hashfn_(element), hash); |
| size_t index = IndexForHash(hash); |
| while (true) { |
| T& slot = ElementForIndex(index); |
| if (emptyfn_.IsEmpty(slot)) { |
| return end(); |
| } |
| if (pred_(slot, element)) { |
| return Iterator(this, index); |
| } |
| index = NextIndex(index); |
| } |
| } |
| // Insert an element, allows duplicates. |
| void Insert(const T& element) { |
| InsertWithHash(element, hashfn_(element)); |
| } |
| void InsertWithHash(const T& element, size_t hash) { |
| DCHECK_EQ(hash, hashfn_(element)); |
| if (num_elements_ >= elements_until_expand_) { |
| Expand(); |
| DCHECK_LT(num_elements_, elements_until_expand_); |
| } |
| const size_t index = FirstAvailableSlot(IndexForHash(hash)); |
| data_[index] = element; |
| ++num_elements_; |
| } |
| size_t Size() const { |
| return num_elements_; |
| } |
| void ShrinkToMaximumLoad() { |
| Resize(Size() / max_load_factor_); |
| } |
| // To distance that inserted elements were probed. Used for measuring how good hash functions |
| // are. |
| size_t TotalProbeDistance() const { |
| size_t total = 0; |
| for (size_t i = 0; i < NumBuckets(); ++i) { |
| const T& element = ElementForIndex(i); |
| if (!emptyfn_.IsEmpty(element)) { |
| size_t ideal_location = IndexForHash(hashfn_(element)); |
| if (ideal_location > i) { |
| total += i + NumBuckets() - ideal_location; |
| } else { |
| total += i - ideal_location; |
| } |
| } |
| } |
| return total; |
| } |
| // Calculate the current load factor and return it. |
| double CalculateLoadFactor() const { |
| return static_cast<double>(Size()) / static_cast<double>(NumBuckets()); |
| } |
| // Make sure that everything reinserts in the right spot. Returns the number of errors. |
| size_t Verify() { |
| size_t errors = 0; |
| for (size_t i = 0; i < num_buckets_; ++i) { |
| T& element = data_[i]; |
| if (!emptyfn_.IsEmpty(element)) { |
| T temp; |
| emptyfn_.MakeEmpty(temp); |
| std::swap(temp, element); |
| size_t first_slot = FirstAvailableSlot(IndexForHash(hashfn_(temp))); |
| if (i != first_slot) { |
| LOG(ERROR) << "Element " << i << " should be in slot " << first_slot; |
| ++errors; |
| } |
| std::swap(temp, element); |
| } |
| } |
| return errors; |
| } |
| |
| private: |
| T& ElementForIndex(size_t index) { |
| DCHECK_LT(index, NumBuckets()); |
| DCHECK(data_ != nullptr); |
| return data_[index]; |
| } |
| const T& ElementForIndex(size_t index) const { |
| DCHECK_LT(index, NumBuckets()); |
| DCHECK(data_ != nullptr); |
| return data_[index]; |
| } |
| size_t IndexForHash(size_t hash) const { |
| return hash % num_buckets_; |
| } |
| size_t NextIndex(size_t index) const { |
| if (UNLIKELY(++index >= num_buckets_)) { |
| DCHECK_EQ(index, NumBuckets()); |
| return 0; |
| } |
| return index; |
| } |
| bool IsFreeSlot(size_t index) const { |
| return emptyfn_.IsEmpty(ElementForIndex(index)); |
| } |
| size_t NumBuckets() const { |
| return num_buckets_; |
| } |
| // Allocate a number of buckets. |
| void AllocateStorage(size_t num_buckets) { |
| num_buckets_ = num_buckets; |
| data_ = allocfn_.allocate(num_buckets_); |
| for (size_t i = 0; i < num_buckets_; ++i) { |
| allocfn_.construct(allocfn_.address(data_[i])); |
| emptyfn_.MakeEmpty(data_[i]); |
| } |
| } |
| void DeallocateStorage() { |
| if (num_buckets_ != 0) { |
| for (size_t i = 0; i < NumBuckets(); ++i) { |
| allocfn_.destroy(allocfn_.address(data_[i])); |
| } |
| allocfn_.deallocate(data_, NumBuckets()); |
| data_ = nullptr; |
| num_buckets_ = 0; |
| } |
| } |
| // Expand the set based on the load factors. |
| void Expand() { |
| size_t min_index = static_cast<size_t>(Size() / min_load_factor_); |
| if (min_index < kMinBuckets) { |
| min_index = kMinBuckets; |
| } |
| // Resize based on the minimum load factor. |
| Resize(min_index); |
| // When we hit elements_until_expand_, we are at the max load factor and must expand again. |
| elements_until_expand_ = NumBuckets() * max_load_factor_; |
| } |
| // Expand / shrink the table to the new specified size. |
| void Resize(size_t new_size) { |
| DCHECK_GE(new_size, Size()); |
| T* old_data = data_; |
| size_t old_num_buckets = num_buckets_; |
| // Reinsert all of the old elements. |
| AllocateStorage(new_size); |
| for (size_t i = 0; i < old_num_buckets; ++i) { |
| T& element = old_data[i]; |
| if (!emptyfn_.IsEmpty(element)) { |
| data_[FirstAvailableSlot(IndexForHash(hashfn_(element)))] = std::move(element); |
| } |
| allocfn_.destroy(allocfn_.address(element)); |
| } |
| allocfn_.deallocate(old_data, old_num_buckets); |
| } |
| ALWAYS_INLINE size_t FirstAvailableSlot(size_t index) const { |
| while (!emptyfn_.IsEmpty(data_[index])) { |
| index = NextIndex(index); |
| } |
| return index; |
| } |
| |
| Alloc allocfn_; // Allocator function. |
| HashFn hashfn_; // Hashing function. |
| EmptyFn emptyfn_; // IsEmpty/SetEmpty function. |
| Pred pred_; // Equals function. |
| size_t num_elements_; // Number of inserted elements. |
| size_t num_buckets_; // Number of hash table buckets. |
| size_t elements_until_expand_; // Maxmimum number of elements until we expand the table. |
| T* data_; // Backing storage. |
| double min_load_factor_; |
| double max_load_factor_; |
| |
| friend class Iterator; |
| }; |
| |
| } // namespace art |
| |
| #endif // ART_RUNTIME_BASE_HASH_SET_H_ |