mgl_memory_fixed_size_allocator.h

[詳解]

// SPDX-License-Identifier: Zlib
/* ------------------------------------------------------------------------- */
/* ------------------------------------------------------------------------- */
 
#ifndef INCGUARD_MGL_MEMORY_FIXED_SIZE_ALLOCATOR_H_1653211251
#define INCGUARD_MGL_MEMORY_FIXED_SIZE_ALLOCATOR_H_1653211251
 
#include <memory>
#include <mutex>
 
namespace MGL::Memory
{
class FixedSizeAllocator
{
public:
    struct Block
    {
        void *address;    
        Block *next;      
    };
 
    //  Note: デフォルトアロケータと絡んでいるため、これ単体で変更しない事！
    enum class Tag : int8_t
    {
        Fixed0 = 0,    
        Fixed1 = 1,    
        Fixed2 = 2,    
        Fixed3 = 3,    
 
        None = -1,     
        Extra = -2,    
    };
 
    struct Header
    {
        Tag tag;              
        int8_t unused;        
        uint16_t usedSize;    
 
        union
        {
            Block *block;          
            size_t requestSize;    
        };
    };
    static_assert(sizeof(Header) <= 16);    // ヘッダサイズは16バイト以下でなければならない
 
    bool Initialize(Tag tag, size_t blockSize, size_t blockCount) noexcept;
 
    /* ------------------------------------------------------------------------- */
    /* ------------------------------------------------------------------------- */
    constexpr void SetAltAllocator(FixedSizeAllocator *altAllocator) noexcept
    {
        _altAllocator = altAllocator;
    }
 
    /* ------------------------------------------------------------------------- */
    /* ------------------------------------------------------------------------- */
    [[nodiscard]] constexpr size_t GetBlockSize() const noexcept
    {
        return _blockSize;
    }
 
    /* ------------------------------------------------------------------------- */
    /* ------------------------------------------------------------------------- */
    [[nodiscard]] constexpr size_t GetCapacity() const noexcept
    {
        return _blockCount;
    }
 
    /* ------------------------------------------------------------------------- */
    /* ------------------------------------------------------------------------- */
    size_t GetFreeCount() noexcept
    {
        const std::lock_guard lock(_mutex);
        return _freeCount;
    }
 
    /* ------------------------------------------------------------------------- */
    /* ------------------------------------------------------------------------- */
    size_t GetUsedCount() noexcept
    {
        return GetCapacity() - GetFreeCount();
    }
 
    void *Allocate(size_t size) noexcept;
    void Deallocate(void *buffer) noexcept;
 
private:
    Tag _tag{Tag::None};
    size_t _blockSize{0};
    size_t _blockCount{0};
    std::unique_ptr<std::byte[]> _pool{nullptr};
    size_t _poolSize{0};
    std::unique_ptr<Block[]> _blockArray{nullptr};
    Block *_topBlock{nullptr};
    size_t _freeCount{0};
    FixedSizeAllocator *_altAllocator{nullptr};
 
    std::mutex _mutex;
};
}    // namespace MGL::Memory
 
#endif    // INCGUARD_MGL_MEMORY_FIXED_SIZE_ALLOCATOR_H_1653211251
 
// vim: et ts=4 sw=4 sts=4