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construct/include/ircd/allocator/dynamic.h

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// 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);
}