The memory_resource class is an abstract interface to an unbounded set of classes encapsulating memory resources.
class memory_resource {
static constexpr size_t max_align = alignof(max_align_t); // exposition only
public:
virtual ~memory_resource();
void* allocate(size_t bytes, size_t alignment = max_align);
void deallocate(void* p, size_t bytes, size_t alignment = max_align);
bool is_equal(const memory_resource& other) const noexcept;
private:
virtual void* do_allocate(size_t bytes, size_t alignment) = 0;
virtual void do_deallocate(void* p, size_t bytes, size_t alignment) = 0;
virtual bool do_is_equal(const memory_resource& other) const noexcept = 0;
};
Effects: Destroys this memory_resource.
void* allocate(size_t bytes, size_t alignment = max_align);
Effects: Equivalent to: return do_allocate(bytes, alignment);
void deallocate(void* p, size_t bytes, size_t alignment = max_align);
Effects: Equivalent to: do_deallocate(p, bytes, alignment);
bool is_equal(const memory_resource& other) const noexcept;
Effects: Equivalent to: return do_is_equal(other);
virtual void* do_allocate(size_t bytes, size_t alignment) = 0;
Requires: alignment shall be a power of two.
Returns: A derived class shall implement this function to return a pointer to allocated storage ([basic.stc.dynamic.deallocation]) with a size of at least bytes. The returned storage is aligned to the specified alignment, if such alignment is supported ([basic.align]); otherwise it is aligned to max_align.
Throws: A derived class implementation shall throw an appropriate exception if it is unable to allocate memory with the requested size and alignment.
virtual void do_deallocate(void* p, size_t bytes, size_t alignment) = 0;
Requires: p shall have been returned from a prior call to allocate(bytes, alignment) on a memory resource equal to *this, and the storage at p shall not yet have been deallocated.
Effects: A derived class shall implement this function to dispose of allocated storage.
Throws: Nothing.
virtual bool do_is_equal(const memory_resource& other) const noexcept = 0;
Returns: A derived class shall implement this function to return true if memory allocated from this can be deallocated from other and vice-versa, otherwise false. [ Note: The most-derived type of other might not match the type of this. For a derived class D, a typical implementation of this function will immediately return false if dynamic_cast<const D*>(&other) == nullptr. — end note ]
bool operator==(const memory_resource& a, const memory_resource& b) noexcept;
Returns: &a == &b || a.is_equal(b).
bool operator!=(const memory_resource& a, const memory_resource& b) noexcept;
Returns: !(a == b).