# scalable_allocator

[memory_allocation.scalable_allocator]

A `scalable_allocator` is a class template that models the allocator requirements from the [allocator.requirements] ISO C++ section.

The `scalable_allocator` allocates and frees memory in a way that scales with the number of processors. Memory allocated by a `scalable_allocator` should be freed by a `scalable_allocator`, not by a `std::allocator`.

    // Defined in header <oneapi/tbb/scalable_allocator.h>

    namespace oneapi {
    namespace tbb {
        template<typename T> class scalable_allocator {
        public:
            using value_type = T;
            using size_type = std::size_t;
            using propagate_on_container_move_assignment = std::true_type;
            using is_always_equal = std::true_type;

            scalable_allocator() = default;
            template<typename U>
            scalable_allocator(const scalable_allocator<U>&) noexcept;

            T* allocate(size_type);
            void deallocate(T*, size_type);
        };
    } // namespace tbb
    } // namespace oneapi

Caution

The `scalable_allocator` requires the memory allocator library. If the library is missing, calls to the scalable allocator fail. In contrast to `scalable_allocator`, if the memory allocator library is not available, `tbb_allocator` falls back on `std::malloc` and `std::free`.

## Member Functions

value_type *allocate(size_type n)

  Allocates `n * sizeof(T)` bytes of memory. Returns a pointer to the allocated memory.

void deallocate(value_type *p, size_type n)

  Deallocates memory pointed to by `p`. The behavior is undefined if the pointer `p` is not the result of the `allocate(n)` method. The behavior is undefined if the memory has been already deallocated.

## Non-member Functions

These functions provide comparison operations between two `scalable_allocator` instances.

    namespace oneapi {
    namespace tbb {
        template<typename T, typename U>
        bool operator==(const scalable_allocator<T>&,
                        const scalable_allocator<U>&) noexcept;

        template<typename T, typename U>
        bool operator!=(const scalable_allocator<T>&,
                        const scalable_allocator<U>&) noexcept;
    } // namespace tbb
    } // namespace oneapi

The namespace where these functions are defined is unspecified, as long as they may be used in respective binary operation expressions on `scalable_allocator` objects. For example, an implementation may define the classes and functions in the same unspecified internal namespace, and define `oneapi::tbb::scalable_allocator` as a type alias for which the non-member functions are reachable only via argument-dependent lookup.

template<typename T, typename U>
bool operator==(const scalable_allocator<T>&, const scalable_allocator<U>&) noexcept

  Returns true.

template<typename T, typename U>
bool operator!=(const scalable_allocator<T>&, const scalable_allocator<U>&) noexcept

  Returns false.