Space Optimized Circular Buffer

circular_buffer_space_optimized<T, Alloc>

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Contents

Description
Synopsis
Rationale
Header Files
Modeled concepts
Template Parameters, Members and StandaloneFunctions
Semantics
See also
Acknowledgments

Description

The circular_buffer_space_optimized container is an adaptor of the circular_buffer. The functionality of the circular_buffer_space_optimized is similar to the base circular_buffer except it does not allocate memory at once when created rather it allocates memory as needed. (The predictive memory allocation is similar to typical std::vector implementation.) Moreover the memory is automatically freed as the size of the container decreases.

Space Optimized Circular Buffer
Figure: The memory allocation process of the space optimized circular buffer. The min_capacity represents the minimal guaranteed amount of allocated memory. The allocated memory will never drop under this value. By default the min_capacity is set to 0.

Synopsis

Note that some of the links point to the original circular_buffer if the functionality is the same. 

namespace boost {

template <class T, class Alloc>
class circular_buffer_space_optimized
{
public:
   typedef typename Alloc::value_type value_type;
   typedef typename Alloc::pointer pointer;
   typedef typename Alloc::const_pointer const_pointer;
   typedef typename Alloc::reference reference;
   typedef typename Alloc::const_reference const_reference;
   typedef typename Alloc::size_type size_type;
   typedef typename Alloc::difference_type difference_type;
   typedef Alloc allocator_type;
   typedef implementation-defined const_iterator;
   typedef implementation-defined iterator;
   typedef reverse_iterator<const_iterator> const_reverse_iterator;
   typedef reverse_iterator<iterator> reverse_iterator;
   typedef std::pair<pointer, size_type> array_range;
   typedef std::pair<const_pointer, size_type> const_array_range;
   typedef implementation-defined capacity_control;

   explicit circular_buffer_space_optimized(const allocator_type& alloc = allocator_type());
   explicit circular_buffer_space_optimized(capacity_control capacity_ctrl, const allocator_type& alloc = allocator_type());
   circular_buffer_space_optimized(capacity_control capacity_ctrl, const_reference item, const allocator_type& alloc = allocator_type());
   circular_buffer_space_optimized(capacity_control capacity_ctrl, size_type n, const_reference item, const allocator_type& alloc = allocator_type());
   circular_buffer_space_optimized(const circular_buffer_space_optimized<T, Alloc>& cb);
   template <class InputIterator>
      circular_buffer_space_optimized(InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type());
   template <class InputIterator>
      circular_buffer_space_optimized(capacity_control capacity_ctrl, InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type());
   ~circular_buffer_space_optimized();

   allocator_type get_allocator() const;
   allocator_type& get_allocator();
   iterator begin();
   iterator end();
   const_iterator begin() const;
   const_iterator end() const;
   reverse_iterator rbegin();
   reverse_iterator rend();
   const_reverse_iterator rbegin() const;
   const_reverse_iterator rend() const;
   reference operator[](size_type index);
   const_reference operator[](size_type index) const;
   reference at(size_type index);
   const_reference at(size_type index) const;
   reference front();
   reference back();
   const_reference front() const;
   const_reference back() const;
   array_range array_one();
   array_range array_two();
   const_array_range array_one() const;
   const_array_range array_two() const;
   pointer linearize();
   size_type size() const;
   size_type max_size() const;
   bool empty() const;
   bool full() const;
   size_type min_capacity() const;
   void set_min_capacity(size_type new_min_capacity);
   size_type capacity() const;
   void set_capacity(size_type new_capacity);
   void resize(size_type new_size, const_reference item = value_type());
   void rset_capacity(size_type new_capacity);
   void rresize(size_type new_size, const_reference item = value_type());
   circular_buffer_space_optimized<T, Alloc>& operator=(const circular_buffer_space_optimized<T, Alloc>& cb);
   void assign(size_type n, const_reference item);
   void assign(capacity_control capacity_ctrl, size_type n, const_reference item);
   template <class InputIterator>
      void assign(InputIterator first, InputIterator last);
   template <class InputIterator>
      void assign(capacity_control capacity_ctrl, InputIterator first, InputIterator last);
   void swap(circular_buffer_space_optimized<T, Alloc>& cb);
   void push_back(const_reference item = value_type());
   void push_front(const_reference item = value_type());
   void pop_back();
   void pop_front();
   iterator insert(iterator pos, const_reference item = value_type());
   void insert(iterator pos, size_type n, const_reference item);
   template <class InputIterator>
      void insert(iterator pos, InputIterator first, InputIterator last);
   iterator rinsert(iterator pos, const_reference item = value_type());
   void rinsert(iterator pos, size_type n, const_reference item);
   template <class InputIterator>
      void rinsert(iterator pos, InputIterator first, InputIterator last);
   iterator erase(iterator pos);
   iterator erase(iterator first, iterator last);
   iterator rerase(iterator pos);
   iterator rerase(iterator first, iterator last);
   void clear();
};

template <class T, class Alloc>
   bool operator==(const circular_buffer_space_optimized<T, Alloc>& lhs, const circular_buffer_space_optimized<T, Alloc>& rhs);
template <class T, class Alloc>
   bool operator<(const circular_buffer_space_optimized<T, Alloc>& lhs, const circular_buffer_space_optimized<T, Alloc>& rhs);
template <class T, class Alloc>
   bool operator!=(const circular_buffer_space_optimized<T, Alloc>& lhs, const circular_buffer_space_optimized<T, Alloc>& rhs);
template <class T, class Alloc>
   bool operator>(const circular_buffer_space_optimized<T, Alloc>& lhs, const circular_buffer_space_optimized<T, Alloc>& rhs);
template <class T, class Alloc>
   bool operator<=(const circular_buffer_space_optimized<T, Alloc>& lhs, const circular_buffer_space_optimized<T, Alloc>& rhs);
template <class T, class Alloc>
   bool operator>=(const circular_buffer_space_optimized<T, Alloc>& lhs, const circular_buffer_space_optimized<T, Alloc>& rhs);
template <class T, class Alloc>
   void swap(circular_buffer_space_optimized<T, Alloc>& lhs, circular_buffer_space_optimized<T, Alloc>& rhs);

} // namespace boost

Rationale

The auto-resizing mode of the space optimized circular buffer can be useful in situations when the container can possibly store large number of elements but most of its lifetime the container stores just few of them. The usage of the circular_buffer_space_optimized will result in decreased memory consumption and can improve the CPU cache effectiveness.


Header Files

The circular_buffer_space_optimized is defined in the file boost/circular_buffer.hpp . There is also a forward declaration for the circular_buffer_space_optimized in the header file boost/circular_buffer_fwd.hpp .


Modeled concepts

Random AccessContainer, Front Insertion Sequence and Back Insertion Sequence.


Template Parameters, Members and Friend Functions

Template parameters, members and friend functions of the circular_buffer_space_optimized are almost the same as for the base circular_buffer . Refer the circular_buffer documentation and also its source code documentation for a detailed description.

Type Description
capacity_control Capacity controller of the space optimized circular buffer. 
    struct capacity_control {
       capacity_control(size_type capacity, size_type min_capacity = 0) m_capacity(capacity), m_min_capacity(min_capacity) {};
       size_type m_capacity;
       size_type m_min_capacity;
    };
Precondition:
capacity >= min_capacity
The m_capacity denotes the capacity of the circular_buffer_space_optimized and the m_min_capacity determines the minimal allocated size of its internal buffer. The converting constructor of the capacity_control allows implicit conversion from size_type like types which ensures compatibility of creating an instance of the circular_buffer_space_optimized with other STL containers.

The specific methods of the circular_buffer_space_optimized are listed below.


Constructors

explicit circular_buffer_space_optimized(const allocator_type& alloc = allocator_type());

Create an empty space optimized circular buffer with a maximum capacity. TODO - doc
explicit circular_buffer_space_optimized(capacity_control capacity_ctrl, const allocator_type& alloc = allocator_type());

Create an empty space optimized circular buffer with a given capacity.
Parameters:
capacity - The capacity of the buffer.
min_capacity - The minimal guaranteed amount of allocated memory. (The metrics of the min_capacity is number of items.)
alloc - The allocator.
Precondition:
capacity >= min_capacity
Postcondition:
(*this).capacity() == capacity && (*this).size == 0
Allocates memory specified by the min_capacity parameter.
Throws:
An allocation error if memory is exhausted (std::bad_alloc if the standard allocator is used).
Note:
It is considered as a bug if the precondition is not met (i.e. if capacity < min_capacity) and an assertion will be invoked in the debug mode.
circular_buffer_space_optimized(capacity_control capacity_ctrl, const_reference item, const allocator_type& alloc = allocator_type());

Create a full space optimized circular buffer filled with copies of item.
Parameters:
capacity - The capacity of the buffer.
min_capacity - The minimal guaranteed amount of allocated memory. (The metrics of the min_capacity is number of items.)
item - The item to be filled with.
alloc - The allocator.
Precondition:
capacity >= min_capacity
Postcondition:
(*this).size() == capacity && (*this)[0] == (*this)[1] == ... == (*this).back() == item
Throws:
An allocation error if memory is exhausted (std::bad_alloc if the standard allocator is used).
Whatever T::T(const T&) throws.
Note:
It is considered as a bug if the precondition is not met (i.e. if capacity < min_capacity) and an assertion will be invoked in the debug mode.
circular_buffer_space_optimized(capacity_control capacity_ctrl, size_type n, const_reference item, const allocator_type& alloc = allocator_type());

TODO doc.
circular_buffer_space_optimized(const circular_buffer_space_optimized<T,Alloc>& cb);

TODO doc.
template <class InputIterator>
circular_buffer_space_optimized(InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type());

TODO doc.
template <class InputIterator>
circular_buffer_space_optimized(capacity_control capacity_ctrl, InputIterator first, InputIterator last, const allocator_type& alloc = allocator_type());

Create a space optimized circular buffer with a copy of a range.
Parameters:
capacity - The capacity of the buffer.
min_capacity - The minimal guaranteed amount of allocated memory. (The metrics of the min_capacity is number of items.)
first - The beginning of the range.
last - The end of the range.
alloc - The allocator.
Precondition:
capacity >= min_capacity and valid range [first, last).
Postcondition:
(*this).capacity() == capacity
Allocates at least as much memory as specified by the - TODO change min_capacity parameter.
If the number of items to copy from the range [first, last) is greater than the specified capacity then only elements from the range [last - capacity, last) will be copied.
Throws:
An allocation error if memory is exhausted (std::bad_alloc if the standard allocator is used).
Whatever T::T(const T&) throws.
Note:
It is considered as a bug if the precondition is not met (i.e. if capacity < min_capacity) and an assertion will be invoked in the debug mode.
~circular_buffer_space_optimized();

TODO doc.

Public Member Functions

bool full() const;

See the circular_buffer source documentation.
size_type min_capacity() const;

Return the minimal guaranteed amount of allocated memory. The allocated memory will never drop under this value.
void set_min_capacity(size_type new_min_capacity);

Change the minimal guaranteed amount of allocated memory.
Precondition:
(*this).capacity() >= new_min_capacity
Postcondition:
(*this).min_capacity() == new_min_capacity Allocates memory specified by the new_min_capacity parameter.
Note:
It is considered as a bug if the precondition is not met (i.e. if new_min_capacity > (*this).capacity()) and an assertion will be invoked in the debug mode.
size_type capacity() const;

See the circular_buffer source documentation.
void set_capacity(size_type new_capacity);

See the circular_buffer source documentation.
Precondition:
min_capacity() <= new_capacity
Note:
It is considered as a bug if the precondition is not met (i.e. if new_capacity > min_capacity()) and an assertion will be invoked in the debug mode.
void resize(size_type new_size, const_reference item = value_type());

See the circular_buffer source documentation.
void rset_capacity(size_type new_capacity);

See the circular_buffer source documentation.
Precondition:
min_capacity() <= new_capacity
Note:
It is considered as a bug if the precondition is not met (i.e. if new_capacity > min_capacity()) and an assertion will be invoked in the debug mode.
void rresize(size_type new_size, const_reference item = value_type());

See the circular_buffer source documentation.
circular_buffer_space_optimized<T,Alloc>& operator=(const circular_buffer_space_optimized<T,Alloc>& cb);

TODO doc.
void assign(size_type n, const_reference item);

See the circular_buffer source documentation.
void assign(capacity_control capacity_ctrl, size_type n, const_reference item);

See the circular_buffer source documentation.
template <class InputIterator>
void assign(InputIterator first, InputIterator last);

See the circular_buffer source documentation.
template <class InputIterator>
void assign(capacity_control capacity_ctrl, InputIterator first, InputIterator last);

See the circular_buffer source documentation.
void swap(circular_buffer_space_optimized<T,Alloc>& cb);

See the circular_buffer source documentation.
void push_back(const_reference item = value_type());

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
void push_front(const_reference item = value_type());

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
void pop_back();

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
void pop_front();

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
iterator insert(iterator pos, const_reference item = value_type());

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
void insert(iterator pos, size_type n, const_reference item);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
template <class InputIterator>
void insert(iterator pos, InputIterator first, InputIterator last);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
iterator rinsert(iterator pos, const_reference item = value_type());

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
void rinsert(iterator pos, size_type n, const_reference item);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
template <class InputIterator>
void rinsert(iterator pos, InputIterator first, InputIterator last);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
iterator erase(iterator pos);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
iterator erase(iterator first, iterator last);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
iterator rerase(iterator pos);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
iterator rerase(iterator first, iterator last);

See the circular_buffer source documentation.
Warning:
The rules for iterator invalidation differ from the original circular_buffer. See the documentation.
void clear();

See the circular_buffer source documentation.

Semantics

TODO remove this section

The behaviour of memory auto-resizing is as follows:

The semantics of the circular_buffer_space_optimized then follows the semantics of the base circular_buffer except the invalidation rules.

The rule for iterator invalidation for circular_buffer_space_optimized is as follows:


See also

boost::circular_buffer, std::vector


Acknowledgments

The idea of the space optimized circular buffer has been introduced by Pavel Vozenilek.