我如何将 scoped_allocator_adaptor 与自定义分配器(包装在 class 中)一起使用,以便它可以针对某些类型而不是 STL 容器展开?
How can I use scoped_allocator_adaptor with a custom allocator (wrapped in a class) so that it can be unwrapped for some types but not STL containers?
我不知道如何更好地表达我的问题。
我对 std::scoped_allocator_adaptor
的理解是,它会将分配器实例传递给容器并将其用于通过 emplace_back
在容器中构建的 elements/containers 的构造,如果它们需要这样的分配器参数)。
我有以下内容,它有点冗长,但这是我能做到的最低限度说明我正在尝试做的事情:
#include <cstdint>
#include <cstdlib>
#include <memory>
#include <vector>
#include <scoped_allocator>
#include <concepts>
namespace custom_memory
{
class CustomAllocator
{
public:
CustomAllocator(const std::size_t sizeBytes,
void* const start)
:
m_sizeBytes(sizeBytes),
m_usedBytes(0),
m_start(start),
m_current(start)
{
}
void* Allocate(const std::size_t& numBytes,
const std::uintptr_t& alignment)
{
std::size_t space = m_sizeBytes - m_usedBytes;
if(std::align(alignment, numBytes, m_current, space))
{
// the amount used for alignment
m_usedBytes += (m_sizeBytes-m_usedBytes) - space;
// the amount actually needed
m_usedBytes += numBytes;
void* address = m_current;
m_current = reinterpret_cast<void*>(
reinterpret_cast<std::uintptr_t>(m_current) + numBytes);
return address;
}
throw std::bad_alloc();
}
void Free(void* const ptr)
{
// do nothing in this Allocator, but other derived types may
}
void Clear()
{
m_current = m_start;
m_usedBytes = 0;
}
std::size_t GetSize() const { return m_sizeBytes; }
protected:
const std::size_t m_sizeBytes;
std::size_t m_usedBytes;
void* const m_start;
void* m_current;
};
// many types derive from base CustomAllocator type
// allows for my custom allocators to be used in STL containers
template<typename T, typename Alloc>
class STLAdaptor
{
public:
typedef T value_type;
STLAdaptor(Alloc* allocator)
:
m_allocator(allocator)
{
}
[[nodiscard]] constexpr T* allocate(std::size_t n)
{
return reinterpret_cast<T*>
(m_allocator->Allocate(n * sizeof(T), alignof(T)));
}
constexpr void deallocate(T* p, std::size_t n)
{
m_allocator->Free(p);
}
std::size_t MaxAllocationSize() const
{
return m_allocator->GetSize();
}
protected:
Alloc* m_allocator;
};
template<typename T, typename Allocator>
using vector = std::vector<T,
std::scoped_allocator_adaptor<STLAdaptor<T, Allocator>>>;
}
// overloads of global new and delete so I can use them with
// my custom allocators
void* operator new(std::size_t size, custom_memory::CustomAllocator& allocator,
std::uintptr_t alignment)
{
return allocator.Allocate(size, alignment);
}
void operator delete(void* ptr, custom_memory::CustomAllocator& allocator)
{
allocator.Free(ptr);
}
// a type that needs an allocator for it's own internal use
template<typename A>
requires std::derived_from<A, custom_memory::CustomAllocator>
struct Foo
{
A* m_allocator;
int* m_foos;
Foo(A* a)
:
m_allocator(a),
m_foos(new (*a, alignof(int)) int(7))
{
}
Foo(const Foo<A>& other)
:
m_allocator(other.m_allocator),
m_foos(new (*m_allocator, alignof(int)) int(*(other.m_foos)))
{
}
~Foo()
{
operator delete (m_foos, *m_allocator);
}
Foo<A>& operator=(const Foo<A>& rhs)
{
m_allocator = rhs.m_allocator;
*m_foos = *(rhs.m_foos);
return *this;
}
};
int main()
{
const std::size_t memSize = 10000000;
void* mem = std::malloc(memSize);
typedef Foo<custom_memory::CustomAllocator> FooType;
custom_memory::CustomAllocator customAlloc(memSize, mem);
// this works
{
std::vector<FooType, custom_memory::STLAdaptor<FooType,
custom_memory::CustomAllocator>>
vec(&customAlloc);
vec.emplace_back(&customAlloc);
}
// this works
{
custom_memory::vector<FooType,custom_memory::CustomAllocator>
vec(&customAlloc);
vec.emplace_back(&customAlloc); // <-- I don't want to pass this
}
// this doesn't work
{
custom_memory::vector<FooType,custom_memory::CustomAllocator>
vec(&customAlloc);
vec.emplace_back(); // <--- I thought scoped_allocator_adaptor
// would pass the allocator to constructed
// elements?
}
// this also doesn't work
{
typedef std::basic_string<char, std::char_traits<char>,
custom_memory::STLAdaptor<char, custom_memory::CustomAllocator>>
StringType;
custom_memory::vector<StringType,custom_memory::CustomAllocator>
vec(&customAlloc);
vec.emplace_back("string");
}
std::free(mem);
return 0;
}
我有一个 CustomAllocator
派生自一个基类(未显示),并且有许多不同的分配器派生自该基类。
我有一个 STLAdaptor
允许 CustomAllocator
在 STL 容器中使用。这是一个模板化的 class,因为上面提到了很多不同的分配器(我实际上有 STLAdaptor
的专门化以及不同的分配器,未显示)。
我已经尝试 typedef
一个 std::vector
,它使用我的 STLAdaptor
包裹 CustomAllocator
在 std::scoped_allocator_adaptor
.
然后我重载全局 new
和 delete
以接受 CustomAllocator
进行分配。
最后,我有一个需要 CustomAllocator
的 class,它在内部使用它为内部类型分配内存(这是我的用例)。
你可以在我的测试中看到我可以:
制作一个成功使用我的 STLAdaptor
包装的 CustomAllocator
的 std::vector
。我可以用 Foo<CustomerAllocator>
类型填充它。
我可以使用我的 std::scoped_allocator_adaptor
std::vector
的 typedef。但是我需要明确地将 CustomAllocator
实例传递给内部类型
我不能省略,但我愿意
我也想使用其他STL容器
我很确定问题是 std::scoped_allocator_adaptor
有一个 STLAdaptor
分配器,而不是 CustomAllocator
。但是后来我也无法让它与 std::string
一起工作,但我认为这与 std::vector
和 std::string
之间具有不同类型的 STLAdaptor
有关(这是 rebind
发挥作用的地方吗?
我正在使用 GCC 10.2.0 和 C++20
如有任何帮助,我们将不胜感激。
I am pretty sure the problem is that std::scoped_allocator_adaptor
has an STLAdaptor
allocator, not a CustomAllocator
.
就目前而言,这是正确的。 scoped_allocator_adaptor
将传递它所拥有的,而不是它不知道的其他类型。
此外,scoped_allocator_adaptor
将使用 uses_allocator
来确定类型是否使用分配器。该特征默认查看类型是否定义了分配器可以转换为的成员类型allocator_type
。
But then I can't get it to work with an std::string
either, but I think that has to do with the STLAdaptor
having different types between the std::vector
and the std::string
(is this where rebind
comes into play?
正确。 STLAdaptor
不符合 the allocator requirements.
我不知道如何更好地表达我的问题。
我对 std::scoped_allocator_adaptor
的理解是,它会将分配器实例传递给容器并将其用于通过 emplace_back
在容器中构建的 elements/containers 的构造,如果它们需要这样的分配器参数)。
我有以下内容,它有点冗长,但这是我能做到的最低限度说明我正在尝试做的事情:
#include <cstdint>
#include <cstdlib>
#include <memory>
#include <vector>
#include <scoped_allocator>
#include <concepts>
namespace custom_memory
{
class CustomAllocator
{
public:
CustomAllocator(const std::size_t sizeBytes,
void* const start)
:
m_sizeBytes(sizeBytes),
m_usedBytes(0),
m_start(start),
m_current(start)
{
}
void* Allocate(const std::size_t& numBytes,
const std::uintptr_t& alignment)
{
std::size_t space = m_sizeBytes - m_usedBytes;
if(std::align(alignment, numBytes, m_current, space))
{
// the amount used for alignment
m_usedBytes += (m_sizeBytes-m_usedBytes) - space;
// the amount actually needed
m_usedBytes += numBytes;
void* address = m_current;
m_current = reinterpret_cast<void*>(
reinterpret_cast<std::uintptr_t>(m_current) + numBytes);
return address;
}
throw std::bad_alloc();
}
void Free(void* const ptr)
{
// do nothing in this Allocator, but other derived types may
}
void Clear()
{
m_current = m_start;
m_usedBytes = 0;
}
std::size_t GetSize() const { return m_sizeBytes; }
protected:
const std::size_t m_sizeBytes;
std::size_t m_usedBytes;
void* const m_start;
void* m_current;
};
// many types derive from base CustomAllocator type
// allows for my custom allocators to be used in STL containers
template<typename T, typename Alloc>
class STLAdaptor
{
public:
typedef T value_type;
STLAdaptor(Alloc* allocator)
:
m_allocator(allocator)
{
}
[[nodiscard]] constexpr T* allocate(std::size_t n)
{
return reinterpret_cast<T*>
(m_allocator->Allocate(n * sizeof(T), alignof(T)));
}
constexpr void deallocate(T* p, std::size_t n)
{
m_allocator->Free(p);
}
std::size_t MaxAllocationSize() const
{
return m_allocator->GetSize();
}
protected:
Alloc* m_allocator;
};
template<typename T, typename Allocator>
using vector = std::vector<T,
std::scoped_allocator_adaptor<STLAdaptor<T, Allocator>>>;
}
// overloads of global new and delete so I can use them with
// my custom allocators
void* operator new(std::size_t size, custom_memory::CustomAllocator& allocator,
std::uintptr_t alignment)
{
return allocator.Allocate(size, alignment);
}
void operator delete(void* ptr, custom_memory::CustomAllocator& allocator)
{
allocator.Free(ptr);
}
// a type that needs an allocator for it's own internal use
template<typename A>
requires std::derived_from<A, custom_memory::CustomAllocator>
struct Foo
{
A* m_allocator;
int* m_foos;
Foo(A* a)
:
m_allocator(a),
m_foos(new (*a, alignof(int)) int(7))
{
}
Foo(const Foo<A>& other)
:
m_allocator(other.m_allocator),
m_foos(new (*m_allocator, alignof(int)) int(*(other.m_foos)))
{
}
~Foo()
{
operator delete (m_foos, *m_allocator);
}
Foo<A>& operator=(const Foo<A>& rhs)
{
m_allocator = rhs.m_allocator;
*m_foos = *(rhs.m_foos);
return *this;
}
};
int main()
{
const std::size_t memSize = 10000000;
void* mem = std::malloc(memSize);
typedef Foo<custom_memory::CustomAllocator> FooType;
custom_memory::CustomAllocator customAlloc(memSize, mem);
// this works
{
std::vector<FooType, custom_memory::STLAdaptor<FooType,
custom_memory::CustomAllocator>>
vec(&customAlloc);
vec.emplace_back(&customAlloc);
}
// this works
{
custom_memory::vector<FooType,custom_memory::CustomAllocator>
vec(&customAlloc);
vec.emplace_back(&customAlloc); // <-- I don't want to pass this
}
// this doesn't work
{
custom_memory::vector<FooType,custom_memory::CustomAllocator>
vec(&customAlloc);
vec.emplace_back(); // <--- I thought scoped_allocator_adaptor
// would pass the allocator to constructed
// elements?
}
// this also doesn't work
{
typedef std::basic_string<char, std::char_traits<char>,
custom_memory::STLAdaptor<char, custom_memory::CustomAllocator>>
StringType;
custom_memory::vector<StringType,custom_memory::CustomAllocator>
vec(&customAlloc);
vec.emplace_back("string");
}
std::free(mem);
return 0;
}
我有一个 CustomAllocator
派生自一个基类(未显示),并且有许多不同的分配器派生自该基类。
我有一个 STLAdaptor
允许 CustomAllocator
在 STL 容器中使用。这是一个模板化的 class,因为上面提到了很多不同的分配器(我实际上有 STLAdaptor
的专门化以及不同的分配器,未显示)。
我已经尝试 typedef
一个 std::vector
,它使用我的 STLAdaptor
包裹 CustomAllocator
在 std::scoped_allocator_adaptor
.
然后我重载全局 new
和 delete
以接受 CustomAllocator
进行分配。
最后,我有一个需要 CustomAllocator
的 class,它在内部使用它为内部类型分配内存(这是我的用例)。
你可以在我的测试中看到我可以:
制作一个成功使用我的
STLAdaptor
包装的CustomAllocator
的std::vector
。我可以用Foo<CustomerAllocator>
类型填充它。我可以使用我的
std::scoped_allocator_adaptor
std::vector
的 typedef。但是我需要明确地将CustomAllocator
实例传递给内部类型我不能省略,但我愿意
我也想使用其他STL容器
我很确定问题是 std::scoped_allocator_adaptor
有一个 STLAdaptor
分配器,而不是 CustomAllocator
。但是后来我也无法让它与 std::string
一起工作,但我认为这与 std::vector
和 std::string
之间具有不同类型的 STLAdaptor
有关(这是 rebind
发挥作用的地方吗?
我正在使用 GCC 10.2.0 和 C++20
如有任何帮助,我们将不胜感激。
I am pretty sure the problem is that
std::scoped_allocator_adaptor
has anSTLAdaptor
allocator, not aCustomAllocator
.
就目前而言,这是正确的。 scoped_allocator_adaptor
将传递它所拥有的,而不是它不知道的其他类型。
此外,scoped_allocator_adaptor
将使用 uses_allocator
来确定类型是否使用分配器。该特征默认查看类型是否定义了分配器可以转换为的成员类型allocator_type
。
But then I can't get it to work with an
std::string
either, but I think that has to do with theSTLAdaptor
having different types between thestd::vector
and thestd::string
(is this whererebind
comes into play?
正确。 STLAdaptor
不符合 the allocator requirements.