construct/include/ircd/allocator/dynamic.h

// Matrix Construct
//
// Copyright (C) Matrix Construct Developers, Authors & Contributors
// Copyright (C) 2016-2023 Jason Volk <jason@zemos.net>
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice is present in all copies. The
// full license for this software is available in the LICENSE file.

#pragma once
#define HAVE_IRCD_ALLOCATOR_DYNAMIC_H

namespace ircd::allocator
{
	template<class T = char>
	struct dynamic;
}

/// The dynamic allocator provides a pool of a fixed size known at runtime.
///
/// This allocator conducts a single new and delete for a pool allowing an STL
/// container to operate without interacting with the rest of the system and
/// without fragmentation. This is not as useful as the allocator::fixed in
/// practice as the standard allocator is as good as this in many cases. This
/// is still available as an analog to the fixed allocator in this suite.
///
template<class T>
struct ircd::allocator::dynamic
:state
{
	struct allocator;

	size_t head_size, data_size;
	std::unique_ptr<uint8_t[]> arena;
	T *buf;

  public:
	allocator operator()();
	operator allocator();

	dynamic(const size_t &size)
	:state{size}
	,head_size{size / 8}
	,data_size{sizeof(T) * size + 16}
	,arena
	{
		new __attribute__((aligned(16))) uint8_t[head_size + data_size]
	}
	,buf
	{
		reinterpret_cast<T *>(arena.get() + head_size + (head_size % 16))
	}
	{
		state::avail = reinterpret_cast<word_t *>(arena.get());
	}
};

/// The actual template passed to containers for using the dynamic allocator.
///
/// See the notes for ircd::allocator::fixed::allocator for details.
///
template<class T>
struct ircd::allocator::dynamic<T>::allocator
{
	using value_type         = T;
	using pointer            = T *;
	using const_pointer      = const T *;
	using reference          = T &;
	using const_reference    = const T &;
	using size_type          = std::size_t;
	using difference_type    = std::ptrdiff_t;

	dynamic *s;

  public:
	template<class U> struct rebind
	{
		using other = typename dynamic<U>::allocator;
	};

	size_type max_size() const                   { return s->size;                                 }
	auto address(reference x) const              { return &x;                                      }
	auto address(const_reference x) const        { return &x;                                      }

	pointer
	__attribute__((malloc, returns_nonnull, warn_unused_result))
	allocate(const size_type &n, const const_pointer &hint = nullptr)
	{
		const uint hintpos(hint? hint - s->buf : -1);
		return s->buf + s->state::allocate(n, hintpos);
	}

	void deallocate(const pointer &p, const size_type &n)
	{
		const uint pos(p - s->buf);
		s->state::deallocate(pos, n);
	}

	template<class U>
	allocator(const typename dynamic<U>::allocator &s) noexcept
	:s{reinterpret_cast<dynamic *>(s.s)}
	{}

	allocator(dynamic &s) noexcept
	:s{&s}
	{}

	allocator(allocator &&) = default;
	allocator(const allocator &) = default;

	friend bool operator==(const allocator &a, const allocator &b)
	{
		return &a == &b;
	}

	friend bool operator!=(const allocator &a, const allocator &b)
	{
		return &a == &b;
	}
};

template<class T>
inline typename ircd::allocator::dynamic<T>::allocator
ircd::allocator::dynamic<T>::operator()()
{
	return ircd::allocator::dynamic<T>::allocator(*this);
}

template<class T>
inline ircd::allocator::dynamic<T>::operator
allocator()
{
	return ircd::allocator::dynamic<T>::allocator(*this);
}