Class template allocator

boost::container::allocator

Synopsis

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

template<typename T, unsigned Version = 2, 
         unsigned int AllocationDisableMask = 0> 
class allocator {
public:
  // types
  typedef T                                                      value_type;     
  typedef T *                                                    pointer;        
  typedef const T *                                              const_pointer;  
  typedef T &                                                    reference;      
  typedef const T &                                              const_reference;
  typedef std::size_t                                            size_type;      
  typedef std::ptrdiff_t                                         difference_type;
  typedef boost::container::dtl::version_type< self_t, Version > version;        

  // member classes/structs/unions
  template<typename T2> 
  struct rebind {
    // types
    typedef allocator< T2, Version, AllocationDisableMask > other;
  };

  // construct/copy/destruct
  allocator() noexcept;
  allocator(const allocator &) noexcept;
  template<typename T2> allocator(const allocator< T2 > &) noexcept;

  // public member functions
  pointer allocate(size_type, const void * = 0);
  void deallocate(pointer, size_type) noexcept;
  size_type max_size() const noexcept;
  pointer allocation_command(allocation_type, size_type, size_type &, 
                             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;

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

  // private member functions
  pointer priv_allocation_command(allocation_type, std::size_t, size_type &, 
                                  pointer &);
};

Description

This class is an extended STL-compatible that offers advanced allocation mechanism (in-place expansion, shrinking, burst-allocation...)

This allocator is a wrapper around a modified DLmalloc. 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.

AllocationDisableMask works only if Version is 2 and it can be an inclusive OR of allocation types the user wants to disable.

`allocator` public construct/copy/destruct

```
allocator() noexcept;
```
Default constructor Never throws
```
allocator(const allocator &) noexcept;
```
Constructor from other allocator. Never throws

template<typename T2> allocator(const allocator< T2 > &) noexcept;

Constructor from related allocator. Never throws

`allocator` public member functions

```
pointer allocate(size_type count, const void * hint = 0);
```
Allocates memory for an array of count elements. Throws std::bad_alloc if there is no enough memory If Version is 2, this allocated memory can only be deallocated with deallocate() or (for Version == 2) deallocate_many()

void deallocate(pointer ptr, size_type) noexcept;

Deallocates previously allocated memory. Never throws

```
size_type max_size() const noexcept;
```
Returns the maximum number of elements that could be allocated. Never throws

pointer allocation_command(allocation_type command, size_type limit_size, 
                           size_type & prefer_in_recvd_out_size, 
                           pointer & reuse);

An advanced function that offers in-place expansion shrink to fit and new allocation capabilities. Memory allocated with this function can only be deallocated with deallocate() or deallocate_many(). This function is available only with Version == 2

```
size_type size(pointer p) const noexcept;
```
Returns maximum the number of objects the previously allocated memory pointed by p can hold. Memory must not have been allocated with allocate_one or allocate_individual. This function is available only with Version == 2
```
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 This function is available only with Version == 2
```
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() This function is available only with Version == 2
```
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() or allocate_individual.
```
void deallocate_individual(multiallocation_chain & chain) noexcept;
```
Deallocates memory allocated with allocate_one() or allocate_individual(). This function is available only with Version == 2
```
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() This function is available only with Version == 2
```
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() This function is available only with Version == 2
```
void deallocate_many(multiallocation_chain & chain) noexcept;
```
Deallocates several elements allocated by allocate_many(), allocate(), or allocation_command(). This function is available only with Version == 2

`allocator` friend functions

```
friend void swap(self_t &, self_t &) noexcept;
```
Swaps two allocators, does nothing because this allocator is stateless
```
friend bool operator==(const allocator &, const allocator &) noexcept;
```
An allocator always compares to true, as memory allocated with one instance can be deallocated by another instance
```
friend bool operator!=(const allocator &, const allocator &) noexcept;
```
An allocator always compares to false, as memory allocated with one instance can be deallocated by another instance

`allocator` private member functions

pointer priv_allocation_command(allocation_type command, 
                                std::size_t limit_size, 
                                size_type & prefer_in_recvd_out_size, 
                                pointer & reuse_ptr);