[mem.res.class] (original) (raw)

20 Memory management library [mem]

20.5 Memory resources [mem.res]

20.5.2 Class memory_resource [mem.res.class]

20.5.2.1 General [mem.res.class.general]

The memory_resource class is an abstract interface to an unbounded set of classes encapsulating memory resources.

namespace std::pmr { class memory_resource { static constexpr size_t max_align = alignof(max_align_t); public: memory_resource() = default; memory_resource(const memory_resource&) = default;virtual ~memory_resource(); memory_resource& operator=(const memory_resource&) = default;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;};}

20.5.2.2 Public member functions [mem.res.public]

Effects: Destroys this memory_resource.

void* allocate(size_t bytes, size_t alignment = max_align);

Effects: Allocates storage by calling do_allocate(bytes, alignment) and implicitly creates objects within the allocated region of storage.

Returns: A pointer to a suitable created object ([intro.object]) in the allocated region of storage.

Throws: What and when the call to do_allocate throws.

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);

20.5.2.3 Private virtual member functions [mem.res.private]

virtual void* do_allocate(size_t bytes, size_t alignment) = 0;

Preconditions: alignment is a power of two.

Returns: A derived class shall implement this function to return a pointer to allocated storage ([basic.stc.dynamic.allocation]) with a size of at least bytes, aligned to the specified alignment.

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;

Preconditions: p was returned from a prior call to allocate(bytes, alignment)on a memory resource equal to *this, and the storage at p has not yet been deallocated.

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

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 1:

It is possible that the most-derived type of other does not match the type of *this.

For a derived class D, an implementation of this function can immediately return falseif dynamic_cast<const D*>(&other) == nullptr.

— _end note_]

20.5.2.4 Equality [mem.res.eq]

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

Returns: &a == &b || a.is_equal(b).