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101 lines
2.4 KiB
C++
101 lines
2.4 KiB
C++
#pragma once
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#include <DB/Common/Arena.h>
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#include <ext/bit_cast.hpp>
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#include <ext/size.hpp>
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#include <cstdlib>
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#include <memory>
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#include <array>
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namespace DB
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{
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class ArenaWithFreeLists : private Allocator<false>
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{
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private:
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struct Block { Block * next; };
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static const std::array<std::size_t, 14> & getSizes()
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{
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static constexpr std::array<std::size_t, 14> sizes{
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8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768, 65536
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};
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static_assert(sizes.front() >= sizeof(Block), "Can't make allocations smaller than sizeof(Block)");
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return sizes;
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}
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static auto sizeToPreviousPowerOfTwo(const int size) { return _bit_scan_reverse(size - 1); }
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static auto getMinBucketNum()
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{
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static const auto val = sizeToPreviousPowerOfTwo(getSizes().front());
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return val;
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}
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static auto getMaxFixedBlockSize() { return getSizes().back(); }
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Arena pool;
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const std::unique_ptr<Block * []> free_lists = std::make_unique<Block * []>(ext::size(getSizes()));
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static std::size_t findFreeListIndex(const std::size_t size)
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{
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/// shift powers of two into previous bucket by subtracting 1
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const auto bucket_num = sizeToPreviousPowerOfTwo(size);
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return std::max(bucket_num, getMinBucketNum()) - getMinBucketNum();
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}
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public:
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ArenaWithFreeLists(
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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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: pool{initial_size, growth_factor, linear_growth_threshold}
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{
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}
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char * alloc(const std::size_t size)
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{
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if (size > getMaxFixedBlockSize())
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return static_cast<char *>(Allocator::alloc(size));
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/// find list of required size
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const auto list_idx = findFreeListIndex(size);
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if (auto & block = free_lists[list_idx])
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{
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const auto res = ext::bit_cast<char *>(block);
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block = block->next;
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return res;
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}
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/// no block of corresponding size, allocate a new one
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return pool.alloc(getSizes()[list_idx]);
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}
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void free(const void * ptr, const std::size_t size)
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{
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if (size > getMaxFixedBlockSize())
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return Allocator::free(const_cast<void *>(ptr), size);
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/// find list of required size
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const auto list_idx = findFreeListIndex(size);
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auto & block = free_lists[list_idx];
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const auto old = block;
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block = ext::bit_cast<Block *>(ptr);
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block->next = old;
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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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