23 General utilities library [utilities]

23.12 Memory resources [mem.res]

23.12.2 Class memory_­resource [mem.res.class]

1
#
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;
};

23.12.2.1 memory_­resource public member functions [mem.res.public]

🔗
~memory_resource();
1
#
Effects: Destroys this memory_­resource.
🔗
void* allocate(size_t bytes, size_t alignment = max_align);
2
#
Effects: Equivalent to: return do_­allocate(bytes, alignment);
🔗
void deallocate(void* p, size_t bytes, size_t alignment = max_align);
3
#
Effects: Equivalent to: do_­deallocate(p, bytes, alignment);
🔗
bool is_equal(const memory_resource& other) const noexcept;
4
#
Effects: Equivalent to: return do_­is_­equal(other);

23.12.2.2 memory_­resource private virtual member functions [mem.res.private]

🔗
virtual void* do_allocate(size_t bytes, size_t alignment) = 0;
1
#
Requires: alignment shall be a power of two.
2
#
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.
3
#
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;
4
#
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.
5
#
Effects: A derived class shall implement this function to dispose of allocated storage.
6
#
Throws: Nothing.
🔗
virtual bool do_is_equal(const memory_resource& other) const noexcept = 0;
7
#
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
 ]

23.12.2.3 memory_­resource equality [mem.res.eq]

🔗
bool operator==(const memory_resource& a, const memory_resource& b) noexcept;
1
#
Returns: &a == &b || a.is_­equal(b).
🔗
bool operator!=(const memory_resource& a, const memory_resource& b) noexcept;
2
#
Returns: !(a == b).