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MDEV-30289: Implement small_vector for mtr_t::m_memo
To avoid heap memory allocation overhead for mtr_t::m_memo, we will allocate a small number of elements statically in mtr_t::m_memo::small. Only if that preallocated data is insufficient, we will invoke my_alloc() or my_realloc() for more storage. The implementation of the data structure is inspired by llvm::SmallVector.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,97 @@ | ||
| /***************************************************************************** | ||
| Copyright (c) 2023, MariaDB Corporation. | ||
| This program is free software; you can redistribute it and/or modify it under | ||
| the terms of the GNU General Public License as published by the Free Software | ||
| Foundation; version 2 of the License. | ||
| This program is distributed in the hope that it will be useful, but WITHOUT | ||
| ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS | ||
| FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. | ||
| You should have received a copy of the GNU General Public License along with | ||
| this program; if not, write to the Free Software Foundation, Inc., | ||
| 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA | ||
| *****************************************************************************/ | ||
|
|
||
| #pragma once | ||
| /* A normally small vector, inspired by llvm::SmallVector */ | ||
| #include "my_global.h" | ||
| #include <iterator> | ||
| #include <memory> | ||
|
|
||
| class small_vector_base | ||
| { | ||
| protected: | ||
| typedef uint32_t Size_T; | ||
| void *BeginX; | ||
| Size_T Size= 0, Capacity; | ||
| small_vector_base()= delete; | ||
| small_vector_base(void *small, size_t small_size) | ||
| : BeginX(small), Capacity(Size_T(small_size)) {} | ||
| ATTRIBUTE_COLD void grow_by_1(void *small, size_t element_size); | ||
| public: | ||
| size_t size() const { return Size; } | ||
| size_t capacity() const { return Capacity; } | ||
| bool empty() const { return !Size; } | ||
| void clear() { Size= 0; } | ||
| protected: | ||
| void set_size(size_t N) { Size= Size_T(N); } | ||
| }; | ||
|
|
||
| template <typename T, unsigned N> | ||
| class small_vector : public small_vector_base | ||
| { | ||
| /** The fixed storage allocation */ | ||
| T small[N]; | ||
|
|
||
| using small_vector_base::set_size; | ||
|
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| void grow_if_needed() | ||
| { | ||
| if (unlikely(size() >= capacity())) | ||
| grow_by_1(small, sizeof *small); | ||
| } | ||
|
|
||
| public: | ||
| small_vector() : small_vector_base(small, N) | ||
| { | ||
| TRASH_ALLOC(small, sizeof small); | ||
| } | ||
| ~small_vector() | ||
| { | ||
| if (small != begin()) | ||
| my_free(begin()); | ||
| MEM_MAKE_ADDRESSABLE(small, sizeof small); | ||
| } | ||
|
|
||
| using iterator= T *; | ||
| using const_iterator= const T *; | ||
| using reverse_iterator= std::reverse_iterator<iterator>; | ||
| using reference= T &; | ||
|
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| iterator begin() { return static_cast<iterator>(BeginX); } | ||
| const_iterator begin() const { return static_cast<const_iterator>(BeginX); } | ||
| iterator end() { return begin() + size(); } | ||
| const_iterator end() const { return begin() + size(); } | ||
|
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| reverse_iterator rbegin() { return reverse_iterator(end()); } | ||
| reverse_iterator rend() { return reverse_iterator(begin()); } | ||
|
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| reference operator[](size_t i) { assert(i < size()); return begin()[i]; } | ||
|
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| void erase(const_iterator S, const_iterator E) | ||
| { | ||
| set_size(std::move(const_cast<iterator>(E), end(), | ||
| const_cast<iterator>(S)) - begin()); | ||
| } | ||
|
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| void emplace_back(T &&arg) | ||
| { | ||
| grow_if_needed(); | ||
| ::new (end()) T(arg); | ||
| set_size(size() + 1); | ||
| } | ||
| }; |
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