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construct/include/ircd/allocator/twolevel.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_TWOLEVEL_H
namespace ircd::allocator
{
template<class T = char,
size_t L0_SIZE = 512>
struct twolevel;
}
/// The twolevel allocator uses both a fixed allocator (first level) and then
/// the standard allocator (second level) when the fixed allocator is exhausted.
/// This has the intent that the fixed allocator will mostly be used, but the
/// fallback to the standard allocator is seamlessly available for robustness.
template<class T,
size_t L0_SIZE>
struct ircd::allocator::twolevel
{
struct allocator;
fixed<T, L0_SIZE> l0;
std::allocator<T> l1;
public:
allocator operator()();
operator allocator();
twolevel() = default;
};
template<class T,
size_t L0_SIZE>
struct ircd::allocator::twolevel<T, L0_SIZE>::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;
twolevel *s;
public:
template<class U,
size_t OTHER_L0_SIZE = L0_SIZE>
struct rebind
{
using other = typename twolevel<U, OTHER_L0_SIZE>::allocator;
};
size_type max_size() const
{
return std::numeric_limits<size_type>::max();
}
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)
{
assert(s);
return
s->l0.allocate(std::nothrow, n, hint)?:
s->l1.allocate(n, hint);
}
void deallocate(const pointer &p, const size_type &n)
{
assert(s);
if(likely(s->l0.in_range(p)))
s->l0.deallocate(p, n);
else
s->l1.deallocate(p, n);
}
template<class U,
size_t OTHER_L0_SIZE = L0_SIZE>
allocator(const typename twolevel<U, OTHER_L0_SIZE>::allocator &s) noexcept
:s{reinterpret_cast<twolevel<T, L0_SIZE> *>(s.s)}
{
static_assert(OTHER_L0_SIZE == L0_SIZE);
}
allocator(twolevel &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,
size_t L0_SIZE>
inline typename ircd::allocator::twolevel<T, L0_SIZE>::allocator
ircd::allocator::twolevel<T, L0_SIZE>::operator()()
{
return ircd::allocator::twolevel<T, L0_SIZE>::allocator(*this);
}
template<class T,
size_t L0_SIZE>
inline ircd::allocator::twolevel<T, L0_SIZE>::operator
allocator()
{
return ircd::allocator::twolevel<T, L0_SIZE>::allocator(*this);
}