mirror of
https://github.com/SerenityOS/serenity
synced 2024-07-22 10:36:24 +00:00
eb02425ef9
Usually the values of the previous and next pointers of deleted buckets are never used, as they're not part of the main ordered bucket chain, but if an in-place rehashing is done, which results in the bucket being turned into a free bucket, the stale pointers will remain, at which point any item that is inserted into said free-bucket will have either a stale previous pointer if the HashTable was empty on insertion, or a stale next pointer, resulting in undefined behaviour. This commit also includes a new HashMap test that reproduces this issue
727 lines
23 KiB
C++
727 lines
23 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/Concepts.h>
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#include <AK/Error.h>
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#include <AK/Forward.h>
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#include <AK/HashFunctions.h>
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#include <AK/StdLibExtras.h>
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#include <AK/Traits.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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KeptExistingEntry
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};
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enum class HashSetExistingEntryBehavior {
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Keep,
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Replace
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};
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// Upper nibble determines state class:
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// - 0: unused bucket
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// - 1: used bucket
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// - F: end bucket
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// Lower nibble determines state within a class.
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enum class BucketState : u8 {
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Free = 0x00,
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Used = 0x10,
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Deleted = 0x01,
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Rehashed = 0x12,
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End = 0xFF,
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};
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// Note that because there's the end state, used and free are not 100% opposites!
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constexpr bool is_used_bucket(BucketState state)
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{
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return (static_cast<u8>(state) & 0xf0) == 0x10;
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}
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constexpr bool is_free_bucket(BucketState state)
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{
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return (static_cast<u8>(state) & 0xf0) == 0x00;
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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==(HashTableIterator const& other) const { return m_bucket == other.m_bucket; }
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bool operator!=(HashTableIterator const& 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->state == BucketState::Used)
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return;
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} while (m_bucket->state != BucketState::End);
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if (m_bucket->state == BucketState::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 OrderedHashTableType, typename T, typename BucketType>
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class OrderedHashTableIterator {
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friend OrderedHashTableType;
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public:
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bool operator==(OrderedHashTableIterator const& other) const { return m_bucket == other.m_bucket; }
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bool operator!=(OrderedHashTableIterator const& 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++() { m_bucket = m_bucket->next; }
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void operator--() { m_bucket = m_bucket->previous; }
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private:
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explicit OrderedHashTableIterator(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, bool IsOrdered>
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class HashTable {
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static constexpr size_t load_factor_in_percent = 60;
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struct Bucket {
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BucketState state;
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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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struct OrderedBucket {
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OrderedBucket* previous;
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OrderedBucket* next;
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BucketState state;
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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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using BucketType = Conditional<IsOrdered, OrderedBucket, Bucket>;
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struct CollectionData {
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};
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struct OrderedCollectionData {
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BucketType* head { nullptr };
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BucketType* tail { nullptr };
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};
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using CollectionDataType = Conditional<IsOrdered, OrderedCollectionData, CollectionData>;
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public:
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HashTable() = default;
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explicit HashTable(size_t capacity) { rehash(capacity); }
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~HashTable()
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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 (is_used_bucket(m_buckets[i].state))
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m_buckets[i].slot()->~T();
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}
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kfree_sized(m_buckets, size_in_bytes(m_capacity));
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}
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HashTable(HashTable const& 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=(HashTable const& other)
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{
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HashTable temporary(other);
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swap(*this, temporary);
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return *this;
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}
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HashTable(HashTable&& other) noexcept
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: m_buckets(other.m_buckets)
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, m_collection_data(other.m_collection_data)
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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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if constexpr (IsOrdered)
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other.m_collection_data = { nullptr, nullptr };
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}
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HashTable& operator=(HashTable&& other) noexcept
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{
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HashTable temporary { move(other) };
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swap(*this, temporary);
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return *this;
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}
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friend void swap(HashTable& a, HashTable& b) noexcept
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{
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swap(a.m_buckets, b.m_buckets);
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swap(a.m_size, b.m_size);
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swap(a.m_capacity, b.m_capacity);
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swap(a.m_deleted_count, b.m_deleted_count);
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if constexpr (IsOrdered)
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swap(a.m_collection_data, b.m_collection_data);
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}
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[[nodiscard]] bool is_empty() const { return m_size == 0; }
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[[nodiscard]] size_t size() const { return m_size; }
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[[nodiscard]] size_t capacity() const { return m_capacity; }
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template<typename U, size_t N>
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ErrorOr<void> try_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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TRY(try_set(from_array[i]));
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return {};
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}
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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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MUST(try_set_from(from_array));
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}
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void ensure_capacity(size_t capacity)
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{
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VERIFY(capacity >= size());
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rehash(capacity * 2);
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}
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ErrorOr<void> try_ensure_capacity(size_t capacity)
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{
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VERIFY(capacity >= size());
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return try_rehash(capacity * 2);
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}
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[[nodiscard]] bool contains(T const& value) const
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{
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return find(value) != end();
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}
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template<Concepts::HashCompatible<T> K>
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requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] bool contains(K const& value) const
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{
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return find(value) != end();
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}
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using Iterator = Conditional<IsOrdered,
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OrderedHashTableIterator<HashTable, T, BucketType>,
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HashTableIterator<HashTable, T, BucketType>>;
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[[nodiscard]] Iterator begin()
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{
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if constexpr (IsOrdered)
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return Iterator(m_collection_data.head);
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for (size_t i = 0; i < m_capacity; ++i) {
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if (is_used_bucket(m_buckets[i].state))
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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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[[nodiscard]] Iterator end()
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{
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return Iterator(nullptr);
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}
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using ConstIterator = Conditional<IsOrdered,
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OrderedHashTableIterator<const HashTable, const T, const BucketType>,
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HashTableIterator<const HashTable, const T, const BucketType>>;
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[[nodiscard]] ConstIterator begin() const
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{
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if constexpr (IsOrdered)
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return ConstIterator(m_collection_data.head);
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for (size_t i = 0; i < m_capacity; ++i) {
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if (is_used_bucket(m_buckets[i].state))
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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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[[nodiscard]] 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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*this = HashTable();
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}
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void clear_with_capacity()
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{
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if constexpr (!Detail::IsTriviallyDestructible<T>) {
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for (auto* bucket : *this)
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bucket->~T();
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}
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__builtin_memset(m_buckets, 0, size_in_bytes(capacity()));
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m_size = 0;
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m_deleted_count = 0;
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if constexpr (IsOrdered)
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m_collection_data = { nullptr, nullptr };
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else
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m_buckets[m_capacity].state = BucketState::End;
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}
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template<typename U = T>
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ErrorOr<HashSetResult> try_set(U&& value, HashSetExistingEntryBehavior existing_entry_behavior = HashSetExistingEntryBehavior::Replace)
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{
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auto* bucket = TRY(try_lookup_for_writing(value));
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if (is_used_bucket(bucket->state)) {
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if (existing_entry_behavior == HashSetExistingEntryBehavior::Keep)
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return HashSetResult::KeptExistingEntry;
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(*bucket->slot()) = forward<U>(value);
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return HashSetResult::ReplacedExistingEntry;
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}
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new (bucket->slot()) T(forward<U>(value));
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if (bucket->state == BucketState::Deleted)
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--m_deleted_count;
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bucket->state = BucketState::Used;
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if constexpr (IsOrdered) {
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if (!m_collection_data.head) [[unlikely]] {
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m_collection_data.head = bucket;
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} else {
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bucket->previous = m_collection_data.tail;
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m_collection_data.tail->next = bucket;
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}
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m_collection_data.tail = bucket;
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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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template<typename U = T>
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HashSetResult set(U&& value, HashSetExistingEntryBehavior existing_entry_behaviour = HashSetExistingEntryBehavior::Replace)
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{
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return MUST(try_set(forward<U>(value), existing_entry_behaviour));
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}
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template<typename TUnaryPredicate>
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[[nodiscard]] Iterator find(unsigned hash, TUnaryPredicate predicate)
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{
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return Iterator(lookup_with_hash(hash, move(predicate)));
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}
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[[nodiscard]] Iterator find(T const& 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 TUnaryPredicate>
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[[nodiscard]] ConstIterator find(unsigned hash, TUnaryPredicate predicate) const
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{
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return ConstIterator(lookup_with_hash(hash, move(predicate)));
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}
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[[nodiscard]] ConstIterator find(T const& 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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// FIXME: Support for predicates, while guaranteeing that the predicate call
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// does not call a non trivial constructor each time invoked
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template<Concepts::HashCompatible<T> K>
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requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] Iterator find(K const& value)
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{
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return find(Traits<K>::hash(value), [&](auto& other) { return Traits<T>::equals(other, value); });
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}
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template<Concepts::HashCompatible<T> K, typename TUnaryPredicate>
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requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] Iterator find(K const& value, TUnaryPredicate predicate)
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{
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return find(Traits<K>::hash(value), move(predicate));
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}
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template<Concepts::HashCompatible<T> K>
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requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] ConstIterator find(K const& value) const
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{
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return find(Traits<K>::hash(value), [&](auto& other) { return Traits<T>::equals(other, value); });
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}
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template<Concepts::HashCompatible<T> K, typename TUnaryPredicate>
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requires(IsSame<TraitsForT, Traits<T>>) [[nodiscard]] ConstIterator find(K const& value, TUnaryPredicate predicate) const
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{
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return find(Traits<K>::hash(value), move(predicate));
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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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template<Concepts::HashCompatible<T> K>
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requires(IsSame<TraitsForT, Traits<T>>) bool remove(K const& 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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VERIFY(iterator.m_bucket);
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auto& bucket = *iterator.m_bucket;
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VERIFY(is_used_bucket(bucket.state));
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delete_bucket(bucket);
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--m_size;
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++m_deleted_count;
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rehash_in_place_if_needed();
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}
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template<typename TUnaryPredicate>
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bool remove_all_matching(TUnaryPredicate const& predicate)
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{
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size_t removed_count = 0;
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for (size_t i = 0; i < m_capacity; ++i) {
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auto& bucket = m_buckets[i];
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if (is_used_bucket(bucket.state) && predicate(*bucket.slot())) {
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delete_bucket(bucket);
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++removed_count;
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}
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}
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if (removed_count) {
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m_deleted_count += removed_count;
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m_size -= removed_count;
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}
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rehash_in_place_if_needed();
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return removed_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.state = BucketState::Used;
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if constexpr (IsOrdered) {
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if (!m_collection_data.head) [[unlikely]] {
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m_collection_data.head = &bucket;
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} else {
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bucket.previous = m_collection_data.tail;
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m_collection_data.tail->next = &bucket;
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}
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m_collection_data.tail = &bucket;
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}
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}
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[[nodiscard]] static constexpr size_t size_in_bytes(size_t capacity)
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{
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if constexpr (IsOrdered) {
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return sizeof(BucketType) * capacity;
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} else {
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return sizeof(BucketType) * (capacity + 1);
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}
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}
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ErrorOr<void> try_rehash(size_t new_capacity)
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{
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if (new_capacity == m_capacity && new_capacity >= 4) {
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rehash_in_place();
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return {};
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}
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new_capacity = max(new_capacity, static_cast<size_t>(4));
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new_capacity = kmalloc_good_size(new_capacity * sizeof(BucketType)) / sizeof(BucketType);
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auto* old_buckets = m_buckets;
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auto old_capacity = m_capacity;
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Iterator old_iter = begin();
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auto* new_buckets = kcalloc(1, size_in_bytes(new_capacity));
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if (!new_buckets)
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return Error::from_errno(ENOMEM);
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m_buckets = (BucketType*)new_buckets;
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m_capacity = new_capacity;
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m_deleted_count = 0;
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if constexpr (IsOrdered)
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m_collection_data = { nullptr, nullptr };
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else
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m_buckets[m_capacity].state = BucketState::End;
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if (!old_buckets)
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return {};
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for (auto it = move(old_iter); it != end(); ++it) {
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insert_during_rehash(move(*it));
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it->~T();
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}
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kfree_sized(old_buckets, size_in_bytes(old_capacity));
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return {};
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}
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void rehash(size_t new_capacity)
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{
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MUST(try_rehash(new_capacity));
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}
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void rehash_in_place()
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{
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// FIXME: This implementation takes two loops over the entire bucket array, but avoids re-allocation.
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// Please benchmark your new implementation before you replace this.
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// The reason is that because of collisions, we use the special "rehashed" bucket state to mark already-rehashed used buckets.
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// Because we of course want to write into old used buckets, but already rehashed data shall not be touched.
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// FIXME: Find a way to reduce the cognitive complexity of this function.
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for (size_t i = 0; i < m_capacity; ++i) {
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auto& bucket = m_buckets[i];
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// FIXME: Bail out when we have handled every filled bucket.
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if (bucket.state == BucketState::Rehashed || bucket.state == BucketState::End || bucket.state == BucketState::Free)
|
|
continue;
|
|
if (bucket.state == BucketState::Deleted) {
|
|
bucket.state = BucketState::Free;
|
|
continue;
|
|
}
|
|
|
|
auto const new_hash = TraitsForT::hash(*bucket.slot());
|
|
if (new_hash % m_capacity == i) {
|
|
bucket.state = BucketState::Rehashed;
|
|
continue;
|
|
}
|
|
|
|
auto target_hash = new_hash;
|
|
auto const to_move_hash = i;
|
|
BucketType* target_bucket = &m_buckets[target_hash % m_capacity];
|
|
BucketType* bucket_to_move = &m_buckets[i];
|
|
|
|
// Try to move the bucket to move into its correct spot.
|
|
// During the procedure, we might re-hash or actually change the bucket to move.
|
|
while (!is_free_bucket(bucket_to_move->state)) {
|
|
|
|
// If we're targeting ourselves, there's nothing to do.
|
|
if (to_move_hash == target_hash % m_capacity) {
|
|
bucket_to_move->state = BucketState::Rehashed;
|
|
break;
|
|
}
|
|
|
|
if (is_free_bucket(target_bucket->state)) {
|
|
// We can just overwrite the target bucket and bail out.
|
|
new (target_bucket->slot()) T(move(*bucket_to_move->slot()));
|
|
target_bucket->state = BucketState::Rehashed;
|
|
bucket_to_move->state = BucketState::Free;
|
|
|
|
if constexpr (IsOrdered) {
|
|
swap(bucket_to_move->previous, target_bucket->previous);
|
|
swap(bucket_to_move->next, target_bucket->next);
|
|
|
|
if (target_bucket->previous)
|
|
target_bucket->previous->next = target_bucket;
|
|
else
|
|
m_collection_data.head = target_bucket;
|
|
if (target_bucket->next)
|
|
target_bucket->next->previous = target_bucket;
|
|
else
|
|
m_collection_data.tail = target_bucket;
|
|
}
|
|
} else if (target_bucket->state == BucketState::Rehashed) {
|
|
// If the target bucket is already re-hashed, we do normal probing.
|
|
target_hash = double_hash(target_hash);
|
|
target_bucket = &m_buckets[target_hash % m_capacity];
|
|
} else {
|
|
VERIFY(target_bucket->state != BucketState::End);
|
|
// The target bucket is a used bucket that hasn't been re-hashed.
|
|
// Swap the data into the target; now the target's data resides in the bucket to move again.
|
|
// (That's of course what we want, how neat!)
|
|
swap(*bucket_to_move->slot(), *target_bucket->slot());
|
|
bucket_to_move->state = target_bucket->state;
|
|
target_bucket->state = BucketState::Rehashed;
|
|
|
|
if constexpr (IsOrdered) {
|
|
// Update state for the target bucket, we'll do the bucket to move later.
|
|
swap(bucket_to_move->previous, target_bucket->previous);
|
|
swap(bucket_to_move->next, target_bucket->next);
|
|
|
|
if (target_bucket->previous)
|
|
target_bucket->previous->next = target_bucket;
|
|
else
|
|
m_collection_data.head = target_bucket;
|
|
if (target_bucket->next)
|
|
target_bucket->next->previous = target_bucket;
|
|
else
|
|
m_collection_data.tail = target_bucket;
|
|
}
|
|
|
|
target_hash = TraitsForT::hash(*bucket_to_move->slot());
|
|
target_bucket = &m_buckets[target_hash % m_capacity];
|
|
|
|
// The data is already in the correct location: Adjust the pointers
|
|
if (target_hash % m_capacity == to_move_hash) {
|
|
bucket_to_move->state = BucketState::Rehashed;
|
|
if constexpr (IsOrdered) {
|
|
// Update state for the bucket to move as it's not actually moved anymore.
|
|
if (bucket_to_move->previous)
|
|
bucket_to_move->previous->next = bucket_to_move;
|
|
else
|
|
m_collection_data.head = bucket_to_move;
|
|
if (bucket_to_move->next)
|
|
bucket_to_move->next->previous = bucket_to_move;
|
|
else
|
|
m_collection_data.tail = bucket_to_move;
|
|
}
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
// After this, the bucket_to_move either contains data that rehashes to itself, or it contains nothing as we were able to move the last thing.
|
|
if (bucket_to_move->state == BucketState::Deleted)
|
|
bucket_to_move->state = BucketState::Free;
|
|
}
|
|
|
|
for (size_t i = 0; i < m_capacity; ++i) {
|
|
if (m_buckets[i].state == BucketState::Rehashed)
|
|
m_buckets[i].state = BucketState::Used;
|
|
}
|
|
|
|
m_deleted_count = 0;
|
|
}
|
|
|
|
void rehash_in_place_if_needed()
|
|
{
|
|
// This signals a "thrashed" hash table with many deleted slots.
|
|
if (m_deleted_count >= m_size && should_grow())
|
|
rehash_in_place();
|
|
}
|
|
|
|
template<typename TUnaryPredicate>
|
|
[[nodiscard]] BucketType* lookup_with_hash(unsigned hash, TUnaryPredicate predicate) const
|
|
{
|
|
if (is_empty())
|
|
return nullptr;
|
|
|
|
for (;;) {
|
|
auto& bucket = m_buckets[hash % m_capacity];
|
|
|
|
if (is_used_bucket(bucket.state) && predicate(*bucket.slot()))
|
|
return &bucket;
|
|
|
|
if (bucket.state != BucketState::Used && bucket.state != BucketState::Deleted)
|
|
return nullptr;
|
|
|
|
hash = double_hash(hash);
|
|
}
|
|
}
|
|
|
|
ErrorOr<BucketType*> try_lookup_for_writing(T const& value)
|
|
{
|
|
// FIXME: Maybe overrun the "allowed" load factor to avoid OOM
|
|
// If we are allowed to do that, separate that logic from
|
|
// the normal lookup_for_writing
|
|
if (should_grow())
|
|
TRY(try_rehash(capacity() * 2));
|
|
auto hash = TraitsForT::hash(value);
|
|
BucketType* first_empty_bucket = nullptr;
|
|
for (;;) {
|
|
auto& bucket = m_buckets[hash % m_capacity];
|
|
|
|
if (is_used_bucket(bucket.state) && TraitsForT::equals(*bucket.slot(), value))
|
|
return &bucket;
|
|
|
|
if (!is_used_bucket(bucket.state)) {
|
|
if (!first_empty_bucket)
|
|
first_empty_bucket = &bucket;
|
|
|
|
if (bucket.state != BucketState::Deleted)
|
|
return const_cast<BucketType*>(first_empty_bucket);
|
|
}
|
|
|
|
hash = double_hash(hash);
|
|
}
|
|
}
|
|
[[nodiscard]] BucketType& lookup_for_writing(T const& value)
|
|
{
|
|
return *MUST(try_lookup_for_writing(value));
|
|
}
|
|
|
|
[[nodiscard]] size_t used_bucket_count() const { return m_size + m_deleted_count; }
|
|
[[nodiscard]] bool should_grow() const { return ((used_bucket_count() + 1) * 100) >= (m_capacity * load_factor_in_percent); }
|
|
|
|
void delete_bucket(auto& bucket)
|
|
{
|
|
bucket.slot()->~T();
|
|
bucket.state = BucketState::Deleted;
|
|
|
|
if constexpr (IsOrdered) {
|
|
if (bucket.previous)
|
|
bucket.previous->next = bucket.next;
|
|
else
|
|
m_collection_data.head = bucket.next;
|
|
bucket.previous = nullptr;
|
|
if (bucket.next)
|
|
bucket.next->previous = bucket.previous;
|
|
else
|
|
m_collection_data.tail = bucket.previous;
|
|
bucket.next = nullptr;
|
|
}
|
|
}
|
|
|
|
BucketType* m_buckets { nullptr };
|
|
|
|
[[no_unique_address]] CollectionDataType m_collection_data;
|
|
size_t m_size { 0 };
|
|
size_t m_capacity { 0 };
|
|
size_t m_deleted_count { 0 };
|
|
};
|
|
}
|
|
|
|
using AK::HashTable;
|
|
using AK::OrderedHashTable;
|