mirror of
https://github.com/SerenityOS/serenity
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![Andreas Kling](/assets/img/avatar_default.png)
Instead of each hash bucket being a SinglyLinkedList, switch to using closed hashing (open addressing). Buckets are chained together via double hashing (hashing the hash until we find an unused bucket.) This greatly reduces malloc traffic, since each added element no longer allocates a new linked list node. Appears performance neutral on test-js. Can definitely be tuned and could use proper management of load factor, etc.
378 lines
10 KiB
C++
378 lines
10 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#pragma once
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#include <AK/HashFunctions.h>
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#include <AK/LogStream.h>
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#include <AK/StdLibExtras.h>
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#include <AK/Types.h>
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#include <AK/kmalloc.h>
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namespace AK {
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enum class HashSetResult {
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InsertedNewEntry,
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ReplacedExistingEntry
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};
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template<typename HashTableType, typename T, typename BucketType>
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class HashTableIterator {
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friend HashTableType;
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public:
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bool operator==(const HashTableIterator& other) const { return m_bucket == other.m_bucket; }
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bool operator!=(const HashTableIterator& other) const { return m_bucket != other.m_bucket; }
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T& operator*() { return *m_bucket->slot(); }
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T* operator->() { return m_bucket->slot(); }
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void operator++() { skip_to_next(); }
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private:
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void skip_to_next()
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{
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if (!m_bucket)
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return;
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do {
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++m_bucket;
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if (m_bucket->used)
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return;
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} while (!m_bucket->end);
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if (m_bucket->end)
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m_bucket = nullptr;
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}
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explicit HashTableIterator(BucketType* bucket)
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: m_bucket(bucket)
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{
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}
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BucketType* m_bucket { nullptr };
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};
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template<typename T, typename TraitsForT>
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class HashTable {
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struct Bucket {
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bool used;
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bool deleted;
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bool end;
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alignas(T) u8 storage[sizeof(T)];
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T* slot() { return reinterpret_cast<T*>(storage); }
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const T* slot() const { return reinterpret_cast<const T*>(storage); }
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};
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public:
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HashTable() { }
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HashTable(size_t capacity) { rehash(capacity); }
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~HashTable() { clear(); }
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HashTable(const HashTable& other)
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{
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rehash(other.capacity());
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for (auto& it : other)
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set(it);
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}
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HashTable& operator=(const HashTable& other)
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{
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if (this != &other) {
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clear();
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rehash(other.capacity());
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for (auto& it : other)
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set(it);
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}
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return *this;
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}
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HashTable(HashTable&& other)
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: m_buckets(other.m_buckets)
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, m_size(other.m_size)
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, m_capacity(other.m_capacity)
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, m_deleted_count(other.m_deleted_count)
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{
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other.m_size = 0;
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other.m_capacity = 0;
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other.m_deleted_count = 0;
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other.m_buckets = nullptr;
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}
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HashTable& operator=(HashTable&& other)
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{
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if (this != &other) {
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clear();
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m_buckets = exchange(other.m_buckets, nullptr);
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m_size = exchange(other.m_size, 0);
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m_capacity = exchange(other.m_capacity, 0);
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m_deleted_count = exchange(other.m_deleted_count, 0);
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}
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return *this;
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}
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bool is_empty() const { return !m_size; }
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size_t size() const { return m_size; }
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size_t capacity() const { return m_capacity; }
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template<typename U, size_t N>
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void set_from(U (&from_array)[N])
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{
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for (size_t i = 0; i < N; ++i) {
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set(from_array[i]);
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}
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}
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void ensure_capacity(size_t capacity)
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{
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ASSERT(capacity >= size());
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rehash(capacity * 2);
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}
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bool contains(const T& value) const
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{
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return find(value) != end();
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}
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using Iterator = HashTableIterator<HashTable, T, Bucket>;
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Iterator begin()
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{
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for (size_t i = 0; i < m_capacity; ++i) {
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if (m_buckets[i].used)
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return Iterator(&m_buckets[i]);
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}
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return end();
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}
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Iterator end()
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{
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return Iterator(nullptr);
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}
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using ConstIterator = HashTableIterator<const HashTable, const T, const Bucket>;
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ConstIterator begin() const
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{
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for (size_t i = 0; i < m_capacity; ++i) {
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if (m_buckets[i].used)
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return ConstIterator(&m_buckets[i]);
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}
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return end();
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}
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ConstIterator end() const
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{
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return ConstIterator(nullptr);
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}
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void clear()
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{
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if (!m_buckets)
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return;
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for (size_t i = 0; i < m_capacity; ++i) {
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if (m_buckets[i].used)
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m_buckets[i].slot()->~T();
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}
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kfree(m_buckets);
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m_buckets = nullptr;
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m_capacity = 0;
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m_size = 0;
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m_deleted_count = 0;
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}
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HashSetResult set(T&& value)
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{
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auto& bucket = lookup_for_writing(value);
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if (bucket.used) {
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(*bucket.slot()) = move(value);
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return HashSetResult::ReplacedExistingEntry;
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}
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new (bucket.slot()) T(move(value));
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bucket.used = true;
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if (bucket.deleted) {
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bucket.deleted = false;
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--m_deleted_count;
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}
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++m_size;
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return HashSetResult::InsertedNewEntry;
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}
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HashSetResult set(const T& value)
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{
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return set(T(value));
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}
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template<typename Finder>
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Iterator find(unsigned hash, Finder finder)
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{
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return Iterator(lookup_with_hash(hash, move(finder)));
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}
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Iterator find(const T& value)
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{
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return find(TraitsForT::hash(value), [&](auto& other) { return TraitsForT::equals(value, other); });
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}
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template<typename Finder>
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ConstIterator find(unsigned hash, Finder finder) const
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{
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return ConstIterator(lookup_with_hash(hash, move(finder)));
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}
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ConstIterator find(const T& value) const
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{
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return find(TraitsForT::hash(value), [&](auto& other) { return TraitsForT::equals(value, other); });
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}
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bool remove(const T& value)
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{
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auto it = find(value);
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if (it != end()) {
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remove(it);
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return true;
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}
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return false;
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}
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void remove(Iterator iterator)
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{
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ASSERT(iterator.m_bucket);
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auto& bucket = *iterator.m_bucket;
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ASSERT(bucket.used);
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ASSERT(!bucket.end);
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ASSERT(!bucket.deleted);
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bucket.slot()->~T();
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bucket.used = false;
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bucket.deleted = true;
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--m_size;
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++m_deleted_count;
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}
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private:
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void insert_during_rehash(T&& value)
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{
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auto& bucket = lookup_for_writing(value);
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new (bucket.slot()) T(move(value));
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bucket.used = true;
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}
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void rehash(size_t new_capacity)
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{
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new_capacity = max(new_capacity, static_cast<size_t>(4));
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auto* old_buckets = m_buckets;
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auto old_capacity = m_capacity;
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m_buckets = (Bucket*)kmalloc(sizeof(Bucket) * (new_capacity + 1));
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__builtin_memset(m_buckets, 0, sizeof(Bucket) * (new_capacity + 1));
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m_capacity = new_capacity;
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m_deleted_count = 0;
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m_buckets[m_capacity].end = true;
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if (!old_buckets)
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return;
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for (size_t i = 0; i < old_capacity; ++i) {
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auto& old_bucket = old_buckets[i];
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if (old_bucket.used) {
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insert_during_rehash(move(*old_bucket.slot()));
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old_bucket.slot()->~T();
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}
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}
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kfree(old_buckets);
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}
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template<typename Finder>
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Bucket* lookup_with_hash(unsigned hash, Finder finder, Bucket** usable_bucket_for_writing = nullptr) const
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{
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if (is_empty())
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return nullptr;
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size_t bucket_index = hash % m_capacity;
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for (;;) {
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auto& bucket = m_buckets[bucket_index];
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if (usable_bucket_for_writing && !*usable_bucket_for_writing && !bucket.used) {
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*usable_bucket_for_writing = &bucket;
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}
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if (bucket.used && finder(*bucket.slot()))
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return &bucket;
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if (!bucket.used && !bucket.deleted)
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return nullptr;
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hash = double_hash(hash);
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bucket_index = hash % m_capacity;
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}
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}
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const Bucket* lookup_for_reading(const T& value) const
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{
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return lookup_with_hash(TraitsForT::hash(value), [&value](auto& entry) { return TraitsForT::equals(entry, value); });
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}
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Bucket& lookup_for_writing(const T& value)
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{
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auto hash = TraitsForT::hash(value);
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Bucket* usable_bucket_for_writing = nullptr;
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if (auto* bucket_for_reading = lookup_with_hash(
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hash,
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[&value](auto& entry) { return TraitsForT::equals(entry, value); },
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&usable_bucket_for_writing)) {
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return *const_cast<Bucket*>(bucket_for_reading);
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}
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if ((used_bucket_count() + 1) >= m_capacity)
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rehash((size() + 1) * 2);
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else if (usable_bucket_for_writing)
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return *usable_bucket_for_writing;
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size_t bucket_index = hash % m_capacity;
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for (;;) {
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auto& bucket = m_buckets[bucket_index];
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if (!bucket.used)
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return bucket;
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hash = double_hash(hash);
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bucket_index = hash % m_capacity;
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}
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}
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size_t used_bucket_count() const { return m_size + m_deleted_count; }
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Bucket* m_buckets { nullptr };
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size_t m_size { 0 };
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size_t m_capacity { 0 };
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size_t m_deleted_count { 0 };
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};
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}
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using AK::HashTable;
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