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86 lines
1.7 KiB
C++
86 lines
1.7 KiB
C++
#pragma once
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#include <DB/Common/Arena.h>
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#include <common/likely.h>
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#include <ext/range.hpp>
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#include <ext/size.hpp>
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#include <ext/bit_cast.hpp>
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#include <cstdlib>
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#include <memory>
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namespace DB
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{
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/** Can allocate memory objects of fixed size with deletion support.
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* For small `object_size`s allocated no less than getMinAllocationSize() bytes. */
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class SmallObjectPool
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{
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private:
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struct Block { Block * next; };
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static constexpr auto getMinAllocationSize() { return sizeof(Block); }
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const std::size_t object_size;
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Arena pool;
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Block * free_list{};
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public:
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SmallObjectPool(
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const std::size_t object_size_, const std::size_t initial_size = 4096, const std::size_t growth_factor = 2,
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const std::size_t linear_growth_threshold = 128 * 1024 * 1024)
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: object_size{std::max(object_size_, getMinAllocationSize())},
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pool{initial_size, growth_factor, linear_growth_threshold}
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{
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if (pool.size() < object_size)
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return;
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const auto num_objects = pool.size() / object_size;
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auto head = free_list = ext::bit_cast<Block *>(pool.alloc(num_objects * object_size));
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for (const auto i : ext::range(0, num_objects - 1))
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{
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(void) i;
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head->next = ext::bit_cast<Block *>(ext::bit_cast<char *>(head) + object_size);
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head = head->next;
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}
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head->next = nullptr;
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}
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char * alloc()
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{
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if (free_list)
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{
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const auto res = reinterpret_cast<char *>(free_list);
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free_list = free_list->next;
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return res;
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}
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return pool.alloc(object_size);
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}
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void free(const void * ptr)
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{
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union {
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const void * p_v;
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Block * block;
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};
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p_v = ptr;
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block->next = free_list;
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free_list = block;
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}
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/// Размер выделенного пула в байтах
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size_t size() const
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{
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return pool.size();
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}
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};
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}
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