BLT/include/blt/std/atomic_allocator.h

#pragma once
/*
 *  Copyright (C) 2024  Brett Terpstra
 *
 *  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, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  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, see <https://www.gnu.org/licenses/>.
 */

#ifndef BLT_ATOMIC_ALLOCATOR_H
#define BLT_ATOMIC_ALLOCATOR_H

#include <optional>
#include <limits>
#include <vector>
#include <blt/std/ranges.h>
#include <blt/std/utility.h>
#include <blt/std/types.h>
#include <blt/std/assert.h>
#include <blt/std/mmap.h>
#include <blt/compatibility.h>
#include <stdexcept>
#include "logging.h"
#include <cstdlib>
#include <atomic>

namespace blt
{
    
    template<typename Alloc = blt::aligned_huge_allocator>
    class atomic_bump_allocator
    {
        private:
            struct block
            {
                struct block_metadata_t
                {
                    const blt::size_t size = 0;
                    std::atomic<blt::size_t> allocated_objects = 0;
                    std::atomic<block*> next = nullptr;
                    std::atomic<block*> prev = nullptr;
                    std::atomic<blt::u8*> offset = nullptr;
                } metadata;
                blt::u8 buffer[8]{};
                
                explicit block(blt::size_t size)
                {
                    metadata.size = size;
                    metadata.offset = buffer;
                }
                
                [[nodiscard]] blt::ptrdiff_t storage_size() const noexcept
                {
                    return static_cast<blt::ptrdiff_t>(metadata.size - sizeof(typename block::block_metadata_t));
                }
                
                [[nodiscard]] blt::ptrdiff_t used_bytes_in_block() const noexcept
                {
                    return static_cast<blt::ptrdiff_t>(metadata.offset - buffer);
                }
                
                [[nodiscard]] blt::ptrdiff_t remaining_bytes_in_block() const noexcept
                {
                    return storage_size() - used_bytes_in_block();
                }
            };
        
        public:
            void* allocate(blt::size_t bytes)
            {
                auto head_ptr = head.load(std::memory_order_relaxed);
                auto new_head = head_ptr;
                do
                {
                    if (head_ptr->remaining_bytes_in_block() < bytes)
                    {
                    
                    }
                } while (!head.compare_exchange_weak(head_ptr, new_head, std::memory_order_release, std::memory_order_acquire));
            }
            
            void deallocate(void* ptr)
            {
                auto blk = to_block(ptr);
                --blk.metadata.allocated_objects;
                if (blk.metadata.allocated_objects == 0)
                {
                    if (blk->metadata.prev != nullptr)
                        blk->metadata.prev->metadata.next = blk->metadata.next;
                    if (blk->metadata.next != nullptr)
                        blk->metadata.next->metadata.prev = blk->metadata.prev;
                    alloc.deallocate(blk, blk.metadata.size);
                }
            }
        
        private:
            static inline block* to_block(void* p)
            {
                return reinterpret_cast<block*>(reinterpret_cast<std::uintptr_t>(p) & static_cast<std::uintptr_t>(~(BLT_2MB_SIZE - 1)));
            }
            
            inline block* allocate_block(blt::size_t bytes)
            {
                auto size = align_size_to(bytes, BLT_2MB_SIZE);
                auto ptr = static_cast<block*>(alloc.allocate(size));
                new(ptr) block{size};
                return ptr;
            }
            
            std::atomic<block*> head = nullptr;
            Alloc alloc;
    };
    
}

#endif //BLT_ATOMIC_ALLOCATOR_H