23 General utilities library [utilities]

23.12 Memory resources [mem.res]

23.12.2 Class memory_­resource [mem.res.class]

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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();
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Effects: Destroys this memory_­resource.

void* allocate(size_t bytes, size_t alignment = max_align);
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Effects: Equivalent to: return do_­allocate(bytes, alignment);

void deallocate(void* p, size_t bytes, size_t alignment = max_align);
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Effects: Equivalent to: do_­deallocate(p, bytes, alignment);

bool is_equal(const memory_resource& other) const noexcept;
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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;

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Requires: alignment shall be a power of two.

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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.

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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;

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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.

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Effects: A derived class shall implement this function to dispose of allocated storage.

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Throws: Nothing.

virtual bool do_is_equal(const memory_resource& other) const noexcept = 0;

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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;

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Returns: &a == &b || a.is_­equal(b).

bool operator!=(const memory_resource& a, const memory_resource& b) noexcept;

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Returns: !(a == b).