DynamicArena.h

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/* Copyright (C) 2021 Wildfire Games.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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 */

#ifndef INCLUDED_ALLOCATORS_DYNAMIC_ARENA
#define INCLUDED_ALLOCATORS_DYNAMIC_ARENA

#include "lib/bits.h"

#include <cstdlib>
#include <new> // bad_alloc
#include <utility>
#include <vector>

namespace Allocators {

/**
 * 'Blind' memory allocator. Characteristics:
 * - grows dynamically, and linearily, by BLOCK_SIZE
 * - no reallocations, pointers remain valid
 * - can allocate objects up to BLOCK_SIZE in size
 * - can handle any aligment (up to BLOCK_SIZE)
 * - Doesn't de-allocate unless cleared or destroyed.
 */
template<size_t BLOCK_SIZE>
class DynamicArena
{
protected:
    class Block
    {
    public:
        Block()
        {
            m_Data = static_cast<uint8_t*>(
                std::malloc(BLOCK_SIZE * sizeof(uint8_t)));
            if (!m_Data)
            {
                debug_warn("DynamicArena failed to allocate chunk");
                throw std::bad_alloc();
            }
        }

        ~Block()
        {
            std::free(static_cast<void*>(m_Data));
        }

        Block(const Block& other) = delete;
        Block& operator=(const Block& other) = delete;

        Block(Block&& other)
            : m_Size(other.m_Size), m_Data(other.m_Data)
        {
            other.m_Size = 0;
            other.m_Data = nullptr;
        }

        Block& operator=(Block&& other)
        {
            if (&other == this)
                return *this;

            Block tmp(std::move(other));
            swap(*this, tmp);

            return *this;
        }

        friend void swap(Block& lhs, Block& rhs)
        {
            using std::swap;

            swap(lhs.m_Size, rhs.m_Size);
            swap(lhs.m_Data, rhs.m_Data);
        }

        bool Available(size_t n, size_t alignment) const
        {
            return n + ROUND_UP(m_Size, alignment) <= BLOCK_SIZE;
        }

        uint8_t* Allocate(size_t n, size_t alignment)
        {
            m_Size = ROUND_UP(m_Size, alignment);
            uint8_t* ptr = &m_Data[m_Size];
            m_Size += n;
            return ptr;
        }

    private:
        size_t m_Size = 0;
        uint8_t* m_Data = nullptr;
    };

    NONCOPYABLE(DynamicArena);
public:
    DynamicArena()
    {
        m_Blocks.reserve(16);
        AllocateNewBlock();
    };

    void AllocateNewBlock()
    {
        m_Blocks.emplace_back();
    }

    void* allocate(size_t n, const void*, size_t alignment)
    {
        // Safely handle zero-sized allocations (happens with GCC STL - see ticket #909).
        if (n == 0)
            n = 1;

        if (n > BLOCK_SIZE)
        {
            debug_warn("DynamicArena cannot allocate more than chunk size");
            throw std::bad_alloc();
        }

        if (!m_Blocks.back().Available(n, alignment))
            AllocateNewBlock();

        return reinterpret_cast<void*>(m_Blocks.back().Allocate(n, alignment));
    }

    void deallocate(void* UNUSED(p), size_t UNUSED(n))
    {
        // ignored
    }

    void clear()
    {
        m_Blocks.clear();
        AllocateNewBlock();
    }

protected:
    std::vector<Block> m_Blocks;
};

} // namespace Allocators

#endif // INCLUDED_ALLOCATORS_DYNAMIC_ARENA