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// Copyright (C) 2015-2025 Jonathan Müller and foonathan/memory contributors
// SPDX-License-Identifier: Zlib
#ifndef FOONATHAN_MEMORY_FALLBACK_ALLOCATOR_HPP_INCLUDED
#define FOONATHAN_MEMORY_FALLBACK_ALLOCATOR_HPP_INCLUDED
/// \file
//// Class template \ref foonathan::memory::fallback_allocator.
#include "detail/ebo_storage.hpp"
#include "detail/utility.hpp"
#include "allocator_traits.hpp"
#include "config.hpp"
namespace foonathan
{
namespace memory
{
/// A \concept{raw_allocator,RawAllocator} with a fallback.
/// Allocation first tries `Default`, if it fails,
/// it uses `Fallback`.
/// \requires `Default` must be a composable \concept{concept_rawallocator,RawAllocator},
/// `Fallback` must be a \concept{concept_rawallocator,RawAllocator}.
/// \ingroup adapter
template <class Default, class Fallback>
class fallback_allocator
: FOONATHAN_EBO(detail::ebo_storage<0, typename allocator_traits<Default>::allocator_type>),
FOONATHAN_EBO(detail::ebo_storage<1, typename allocator_traits<Fallback>::allocator_type>)
{
using default_traits = allocator_traits<Default>;
using default_composable_traits = composable_allocator_traits<Default>;
using fallback_traits = allocator_traits<Fallback>;
using fallback_composable_traits = composable_allocator_traits<Fallback>;
using fallback_composable =
is_composable_allocator<typename fallback_traits::allocator_type>;
public:
using default_allocator_type = typename allocator_traits<Default>::allocator_type;
using fallback_allocator_type = typename allocator_traits<Fallback>::allocator_type;
using is_stateful =
std::integral_constant<bool, default_traits::is_stateful::value
|| fallback_traits::is_stateful::value>;
/// \effects Default constructs both allocators.
/// \notes This function only participates in overload resolution, if both allocators are not stateful.
FOONATHAN_ENABLE_IF(!is_stateful::value)
fallback_allocator()
: detail::ebo_storage<0, default_allocator_type>({}),
detail::ebo_storage<1, fallback_allocator_type>({})
{
}
/// \effects Constructs the allocator by passing in the two allocators it has.
explicit fallback_allocator(default_allocator_type&& default_alloc,
fallback_allocator_type&& fallback_alloc = {})
: detail::ebo_storage<0, default_allocator_type>(detail::move(default_alloc)),
detail::ebo_storage<1, fallback_allocator_type>(detail::move(fallback_alloc))
{
}
/// @{
/// \effects First calls the compositioning (de)allocation function on the `default_allocator_type`.
/// If that fails, uses the non-compositioning function of the `fallback_allocator_type`.
void* allocate_node(std::size_t size, std::size_t alignment)
{
auto ptr = default_composable_traits::try_allocate_node(get_default_allocator(),
size, alignment);
if (!ptr)
ptr = fallback_traits::allocate_node(get_fallback_allocator(), size, alignment);
return ptr;
}
void* allocate_array(std::size_t count, std::size_t size, std::size_t alignment)
{
auto ptr = default_composable_traits::try_allocate_array(get_default_allocator(),
count, size, alignment);
if (!ptr)
ptr = fallback_traits::allocate_array(get_fallback_allocator(), count, size,
alignment);
return ptr;
}
void deallocate_node(void* ptr, std::size_t size, std::size_t alignment) noexcept
{
auto res = default_composable_traits::try_deallocate_node(get_default_allocator(),
ptr, size, alignment);
if (!res)
fallback_traits::deallocate_node(get_fallback_allocator(), ptr, size,
alignment);
}
void deallocate_array(void* ptr, std::size_t count, std::size_t size,
std::size_t alignment) noexcept
{
auto res =
default_composable_traits::try_deallocate_array(get_default_allocator(), ptr,
count, size, alignment);
if (!res)
fallback_traits::deallocate_array(get_fallback_allocator(), ptr, count, size,
alignment);
}
/// @}
/// @{
/// \effects First calls the compositioning (de)allocation function on the `default_allocator_type`.
/// If that fails, uses the compositioning function of the `fallback_allocator_type`.
/// \requires The `fallback_allocator_type` msut be composable.
FOONATHAN_ENABLE_IF(fallback_composable::value)
void* try_allocate_node(std::size_t size, std::size_t alignment) noexcept
{
auto ptr = default_composable_traits::try_allocate_node(get_default_allocator(),
size, alignment);
if (!ptr)
ptr = fallback_composable_traits::try_allocate_node(get_fallback_allocator(),
size, alignment);
return ptr;
}
FOONATHAN_ENABLE_IF(fallback_composable::value)
void* allocate_array(std::size_t count, std::size_t size,
std::size_t alignment) noexcept
{
auto ptr = default_composable_traits::try_allocate_array(get_default_allocator(),
count, size, alignment);
if (!ptr)
ptr = fallback_composable_traits::try_allocate_array(get_fallback_allocator(),
count, size, alignment);
return ptr;
}
FOONATHAN_ENABLE_IF(fallback_composable::value)
bool try_deallocate_node(void* ptr, std::size_t size, std::size_t alignment) noexcept
{
auto res = default_composable_traits::try_deallocate_node(get_default_allocator(),
ptr, size, alignment);
if (!res)
res = fallback_composable_traits::try_deallocate_node(get_fallback_allocator(),
ptr, size, alignment);
return res;
}
FOONATHAN_ENABLE_IF(fallback_composable::value)
bool try_deallocate_array(void* ptr, std::size_t count, std::size_t size,
std::size_t alignment) noexcept
{
auto res =
default_composable_traits::try_deallocate_array(get_default_allocator(), ptr,
count, size, alignment);
if (!res)
res = fallback_composable_traits::try_deallocate_array(get_fallback_allocator(),
ptr, count, size,
alignment);
return res;
}
/// @}
/// @{
/// \returns The maximum of the two values from both allocators.
std::size_t max_node_size() const
{
auto def = default_traits::max_node_size(get_default_allocator());
auto fallback = fallback_traits::max_node_size(get_fallback_allocator());
return fallback > def ? fallback : def;
}
std::size_t max_array_size() const
{
auto def = default_traits::max_array_size(get_default_allocator());
auto fallback = fallback_traits::max_array_size(get_fallback_allocator());
return fallback > def ? fallback : def;
}
std::size_t max_alignment() const
{
auto def = default_traits::max_alignment(get_default_allocator());
auto fallback = fallback_traits::max_alignment(get_fallback_allocator());
return fallback > def ? fallback : def;
}
/// @}
/// @{
/// \returns A (`const`) reference to the default allocator.
default_allocator_type& get_default_allocator() noexcept
{
return detail::ebo_storage<0, default_allocator_type>::get();
}
const default_allocator_type& get_default_allocator() const noexcept
{
return detail::ebo_storage<0, default_allocator_type>::get();
}
/// @}
/// @{
/// \returns A (`const`) reference to the fallback allocator.
fallback_allocator_type& get_fallback_allocator() noexcept
{
return detail::ebo_storage<1, fallback_allocator_type>::get();
}
const fallback_allocator_type& get_fallback_allocator() const noexcept
{
return detail::ebo_storage<1, fallback_allocator_type>::get();
}
/// @}
};
} // namespace memory
} // namespace foonathan
#endif // FOONATHAN_MEMORY_FALLBACK_ALLOCATOR_HPP_INCLUDED
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