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## Class template adaptive_pool

boost::container::adaptive_pool

## Synopsis

    // In header: <boost/container/adaptive_pool.hpp>

    template<typename T, std::size_t NodesPerBlock  BOOST_CONTAINER_DOCONLY,
             std::size_t MaxFreeBlocks  BOOST_CONTAINER_DOCONLY,
             std::size_t OverheadPercent  BOOST_CONTAINER_DOCONLY>
    class adaptive_pool {
    public:
      // types
      typedef unsigned int                                                      allocation_type;
      typedef adaptive_pool< T, NodesPerBlock, MaxFreeBlocks, OverheadPercent > self_t;
      typedef T                                                                 value_type;
      typedef T *                                                               pointer;
      typedef const T *                                                         const_pointer;
      typedef unspecified                                                       reference;
      typedef unspecified                                                       const_reference;
      typedef std::size_t                                                       size_type;
      typedef std::ptrdiff_t                                                    difference_type;
      typedef unspecified                                                       version;

      // member classes/structs/unions
      template<typename T2>
      struct rebind {
        // types
        typedef adaptive_pool< T2, NodesPerBlock, MaxFreeBlocks, OverheadPercent > other;
      };

      // construct/copy/destruct
      adaptive_pool() noexcept;
      adaptive_pool(const adaptive_pool &) noexcept;
      template<typename T2>
        adaptive_pool(const adaptive_pool< T2, NodesPerBlock, MaxFreeBlocks, OverheadPercent BOOST_CONTAINER_DOCIGN(BOOST_CONTAINER_I Version)> &) noexcept;
      ~adaptive_pool();

      // public member functions
       BOOST_CONTAINER_DOCIGN(BOOST_STATIC_ASSERT((Version<=2)));
      size_type max_size() const noexcept;
      pointer allocate(size_type, const void * = 0);
      void deallocate(const pointer &, size_type) noexcept;
      std::pair< pointer, bool >
      allocation_command(allocation_type, size_type, size_type, size_type &,
                         pointer = pointer());
      size_type size(pointer) const noexcept;
      pointer allocate_one();
      void allocate_individual(std::size_t, multiallocation_chain &);
      void deallocate_one(pointer) noexcept;
      void deallocate_individual(multiallocation_chain &) noexcept;
      void allocate_many(size_type, std::size_t, multiallocation_chain &);
      void allocate_many(const size_type *, size_type, multiallocation_chain &);
      void deallocate_many(multiallocation_chain &) noexcept;

      // public static functions
      static void deallocate_free_blocks() noexcept;

      // friend functions
      friend void swap(adaptive_pool &, adaptive_pool &) noexcept;
      friend bool operator==(const adaptive_pool &, const adaptive_pool &) noexcept;
      friend bool operator!=(const adaptive_pool &, const adaptive_pool &) noexcept;

      // private member functions
      std::pair< pointer, bool >
      priv_allocation_command(allocation_type, std::size_t, std::size_t,
                              std::size_t &, void *);

      // public data members
      static const std::size_t nodes_per_block;
      static const std::size_t max_free_blocks;
      static const std::size_t overhead_percent;
      static const std::size_t real_nodes_per_block;
    };

## Description

An STL node allocator that uses a modified DLMalloc as memory source.

This node allocator shares a segregated storage between all instances of adaptive_pool with equal sizeof(T).

NodesPerBlock is the number of nodes allocated at once when the allocator needs runs out of nodes. MaxFreeBlocks is the maximum number of totally free blocks that the adaptive node pool will hold. The rest of the totally free blocks will be deallocated to the memory manager.

OverheadPercent is the (approximated) maximum size overhead (1-20%) of the allocator: (memory usable for nodes / total memory allocated from the memory allocator)

### `adaptive_pool` public types

1. typedef unsigned int allocation_type;

   If Version is 1, the allocator is a STL conforming allocator. If Version is 2, the allocator offers advanced expand in place and burst allocation capabilities.

### `adaptive_pool` public construct/copy/destruct

1.     adaptive_pool() noexcept;

   Default constructor.

2.     adaptive_pool(const adaptive_pool &) noexcept;

   Copy constructor from other `adaptive_pool`.

3.     template<typename T2>
         adaptive_pool(const adaptive_pool< T2, NodesPerBlock, MaxFreeBlocks, OverheadPercent BOOST_CONTAINER_DOCIGN(BOOST_CONTAINER_I Version)> &) noexcept;

   Copy constructor from related `adaptive_pool`.

4.     ~adaptive_pool();

   Destructor.

### `adaptive_pool` public member functions

1.      BOOST_CONTAINER_DOCIGN(BOOST_STATIC_ASSERT((Version<=2)));

2.     size_type max_size() const noexcept;

   Returns the number of elements that could be allocated. Never throws

3.     pointer allocate(size_type count, const void * = 0);

   Allocate memory for an array of count elements. Throws std::bad_alloc if there is no enough memory

4.     void deallocate(const pointer & ptr, size_type count) noexcept;

   Deallocate allocated memory. Never throws

5.     std::pair< pointer, bool >
       allocation_command(allocation_type command, size_type limit_size,
                          size_type preferred_size, size_type & received_size,
                          pointer reuse = pointer());

6.     size_type size(pointer p) const noexcept;

   Returns maximum the number of objects the previously allocated memory pointed by p can hold.

7.     pointer allocate_one();

   Allocates just one object. Memory allocated with this function must be deallocated only with deallocate_one(). Throws bad_alloc if there is no enough memory

8.     void allocate_individual(std::size_t num_elements,
                                multiallocation_chain & chain);

   Allocates many elements of size == 1. Elements must be individually deallocated with deallocate_one()

9.     void deallocate_one(pointer p) noexcept;

   Deallocates memory previously allocated with allocate_one(). You should never use deallocate_one to deallocate memory allocated with other functions different from allocate_one(). Never throws

10.     void deallocate_individual(multiallocation_chain & chain) noexcept;

11.     void allocate_many(size_type elem_size, std::size_t n_elements,
                           multiallocation_chain & chain);

    Allocates many elements of size elem_size. Elements must be individually deallocated with deallocate()

12.     void allocate_many(const size_type * elem_sizes, size_type n_elements,
                           multiallocation_chain & chain);

    Allocates n_elements elements, each one of size elem_sizes[i] Elements must be individually deallocated with deallocate()

13.     void deallocate_many(multiallocation_chain & chain) noexcept;

### `adaptive_pool` public static functions

1.     static void deallocate_free_blocks() noexcept;

   Deallocates all free blocks of the pool.

### `adaptive_pool` friend functions

1.     friend void swap(adaptive_pool &, adaptive_pool &) noexcept;

   Swaps allocators. Does not throw. If each allocator is placed in a different memory segment, the result is undefined.

2.     friend bool operator==(const adaptive_pool &, const adaptive_pool &) noexcept;

   An allocator always compares to true, as memory allocated with one instance can be deallocated by another instance

3.     friend bool operator!=(const adaptive_pool &, const adaptive_pool &) noexcept;

   An allocator always compares to false, as memory allocated with one instance can be deallocated by another instance

### `adaptive_pool` private member functions

1.     std::pair< pointer, bool >
       priv_allocation_command(allocation_type command, std::size_t limit_size,
                               std::size_t preferred_size,
                               std::size_t & received_size, void * reuse_ptr);