libcruft-util/cruft/util/alloc/chunked.hpp

/*
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * Copyright 2021, Danny Robson <danny@nerdcruft.net>
 */

#pragma once

#include <memory_resource>

#include <memory>
#include <vector>


///////////////////////////////////////////////////////////////////////////////
namespace cruft::alloc {
    /// An unbounded contiguous allocator that operates on chunks, similar to
    /// a deque.
    ///
    /// It's useful as a means to keep unknown sized allocations in roughly
    /// the same memory region.
    ///
    /// This class models std::pmr::memory_resource.
    class chunked : public std::pmr::memory_resource {
    public:
        static constexpr std::size_t DEFAULT_CHUNK_SIZE = 4096;

        chunked (chunked const&) = default;
        chunked& operator= (chunked const&) = default;

        chunked (chunked&&) noexcept = default;
        chunked& operator= (chunked&&) noexcept = default;

        explicit chunked (std::size_t initial_size);
        chunked (std::size_t initial_size, std::size_t chunk_size);
        ~chunked () noexcept;

    private:
        void* do_allocate (
            std::size_t bytes,
            std::size_t alignment = alignof (std::max_align_t)
        ) override;

        void do_deallocate (
            void *p,
            std::size_t bytes,
            std::size_t alignment = alignof (std::max_align_t)
        ) override;

        bool do_is_equal (memory_resource const&) const noexcept override;

        std::size_t m_chunk;

        struct allocation_t {
            std::size_t size;
            allocation_t*     next;
        };

        union node {
            std::byte *data;
            allocation_t *node;
        };

        struct arena {
            std::byte *head;
            node remain;
        };

        std::vector<arena> m_data;
    };
}