CGAL 5.1 - STL Extensions for CGAL
CGAL::Concurrent_compact_container< T, Allocator > Class Template Reference

#include <CGAL/Concurrent_compact_container.h>

## Definition

An object of the class Concurrent_compact_container is a container of objects of type T, which allows to call insert and erase operations concurrently.

Other operations are not concurrency-safe. For example, one should not parse the container while others are modifying it. It matches all the standard requirements for reversible containers, except that the complexity of its iterator increment and decrement operations is not always guaranteed to be amortized constant time.

This container is not a standard sequence nor associative container, which means the elements are stored in no particular order, and it is not possible to specify a particular place in the iterator sequence where to insert new objects. However, all dereferenceable iterators are still valid after calls to insert() and erase(), except those that have been erased (it behaves similarly to std::list).

The main feature of this container is that it is very memory efficient: its memory size is N*sizeof(T)+o(N), where N is the maximum size that the container has had in its past history, its capacity() (the memory of erased elements is not deallocated until destruction of the container or a call to clear()). This container has been developed in order to store large graph-like data structures like the triangulation and the halfedge data structures.

It supports bidirectional iterators and allows a constant time amortized insert() operation. You cannot specify where to insert new objects (i.e. you don't know where they will end up in the iterator sequence, although insert() returns an iterator pointing to the newly inserted object). You can erase any element with a constant time complexity.

Summary of the differences with std::list: it is more compact in memory since it doesn't store two additional pointers for the iterator needs. It doesn't deallocate elements until the destruction or clear() of the container. The iterator does not have constant amortized time complexity for the increment and decrement operations in all cases, only when not too many elements have not been freed (i.e. when the size() is close to the capacity()). Iterating from begin() to end() takes O(capacity()) time, not size(). In the case where the container has a small size() compared to its capacity(), we advise to "defragment the memory" by copying the container if the iterator performance is needed.

The iterators themselves can be used as T, they provide the necessary functions to be used by Compact_container_traits<T>. Moreover, they also provide a default constructor value which is not singular: it is copyable, comparable, and guaranteed to be unique under comparison (like NULL for pointers). This makes them suitable for use in geometric graphs like handles to vertices in triangulations.

In addition, in a way inspired from the Boost.Intrusive containers, it is possible to construct iterators from references to values in containers using the iterator_to and s_iterator_to functions.

The objects stored in the Concurrent_compact_container can optionally store an "erase counter". If it exists, i.e. if the object is a model of the ObjectWithEraseCounter concept, each time an object is erased from the container, the erase counter of the object will be incremented. For example, this erase counter can be exploited using the CC_safe_handle helper class, so that one can know if a handle is still pointing to the same element. Note that this is meaningful only because the CGAL::Concurrent_compact_container doesn't deallocate elements until the destruction or clear() of the container.

Parameters

The parameter T is required to have a copy constructor and an assignment operator. It also needs to provide access to an internal pointer via Compact_container_traits<T>.

The equality test and the relational order require the operators == and < for T respectively.

The parameter Allocator has to match the standard allocator requirements, with value type T. This parameter has the default value CGAL_ALLOCATOR(T).

## Types

typedef unspecified_type value_type

typedef unspecified_type allocator_type

typedef unspecified_type reference

typedef unspecified_type const_reference

typedef unspecified_type pointer

typedef unspecified_type const_pointer

typedef unspecified_type size_type

typedef unspecified_type difference_type

typedef unspecified_type iterator

typedef unspecified_type const_iterator

typedef unspecified_type reverse_iterator

typedef unspecified_type const_reverse_iterator

## Creation

Concurrent_compact_container (const Allocator &a=Allocator())
introduces an empty container ccc, eventually specifying a particular allocator a as well.

template<class InputIterator >
Concurrent_compact_container (InputIterator first, InputIterator last, const Allocator &a=Allocator())
a container with copies from the range [first,last), eventually specifying a particular allocator.

Concurrent_compact_container (const Concurrent_compact_container &ccc2)
copy constructor. More...

Concurrent_compact_containeroperator= (const Concurrent_compact_container &ccc2)
assignment. More...

void swap (Self &ccc2)
swaps the contents of ccc and ccc2 in constant time complexity. More...

## Access Member Functions

bool is_used (const_iterator pos) const
returns true if the element pos is used (i.e. valid).

iterator begin ()
returns a mutable iterator referring to the first element in ccc.

const_iterator begin () const
returns a constant iterator referring to the first element in ccc.

iterator end ()
returns a mutable iterator which is the past-end-value of ccc.

const_iterator end ()
returns a constant iterator which is the past-end-value of ccc.

reverse_iterator rbegin ()
returns a mutable reverse iterator referring to the reverse beginning in ccc.

const_reverse_iterator rbegin () const
returns a constant reverse iterator referring to the reverse beginning in ccc.

reverse_iterator rend ()
returns a mutable reverse iterator which is the reverse past-end-value of ccc.

const_reverse_iterator rend () const
returns a constant reverse iterator which is the reverse past-end-value of ccc.

iterator iterator_to (reference value) const
returns an iterator which points to value.

const_iterator iterator_to (const_reference value) const
returns a constant iterator which points to value.

bool empty () const
returns true iff ccc is empty.

size_type size () const
returns the number of items in ccc. More...

size_type max_size () const
returns the maximum possible size of the container ccc. More...

size_type capacity () const
returns the total number of elements that ccc can hold without requiring reallocation.

Allocator get_allocator () const
returns the allocator

static iterator s_iterator_to (reference value)
returns an iterator which points to value.

static const_iterator s_iterator_to (const_reference value)
returns a constant iterator which points to value.

## Insertion

template<class T1 >
iterator emplace (const T1 &t1)
constructs an object of type T with the constructor that takes t1 as argument, inserts it in ccc, and returns the iterator pointing to it. More...

iterator insert (const T &t)
inserts a copy of t in ccc and returns the iterator pointing to it.

template<class InputIterator >
void insert (InputIterator first, InputIterator last)
inserts the range [first, last) in ccc.

template<class InputIterator >
void assign (InputIterator first, InputIterator last)
erases all the elements of ccc, then inserts the range [first, last) in ccc.

## Removal

void erase (iterator x)
removes the item pointed by pos from ccc.

void erase (iterator first, iterator last)
removes the items from the range [first, last) from ccc.

void clear ()
all items in ccc are deleted, and the memory is deallocated. More...

## Ownership testing

The following functions are mostly helpful for efficient debugging, since their complexity is $$O(\sqrt{\mathrm{c.capacity()}})$$.

bool owns (const_iterator pos)
returns whether pos is in the range [ccc.begin(), ccc.end()] (ccc.end() included).

bool owns_dereferencable (const_iterator pos)
returns whether pos is in the range [ccc.begin(), ccc.end())(ccc.end() excluded).

## Merging

void merge (Concurrent_compact_container< T, Allocator > &ccc2)
adds the items of ccc2 to the end of ccc and ccc2 becomes empty. More...

## Comparison Operations

bool operator== (const Concurrent_compact_container< T, Allocator > &ccc2) const
test for equality: Two containers are equal, iff they have the same size and if their corresponding elements are equal.

bool operator!= (const Concurrent_compact_container< T, Allocator > &ccc2) const
test for inequality: returns !(ccc == ccc2).

bool operator< (const Concurrent_compact_container< T, Allocator > &ccc2) const
compares in lexicographical order.

bool operator> (const Concurrent_compact_container< T, Allocator > &ccc2) const
returns ccc2 < ccc.

bool operator<= (const Concurrent_compact_container< T, Allocator > &ccc2) const
returns !(ccc > ccc2).

bool operator>= (const Concurrent_compact_container< T, Allocator > &ccc2) const
returns !(ccc < ccc2).

## ◆ Concurrent_compact_container()

template<class T , class Allocator >
 CGAL::Concurrent_compact_container< T, Allocator >::Concurrent_compact_container ( const Concurrent_compact_container< T, Allocator > & ccc2 )

copy constructor.

Each item in ccc2 is copied. The allocator is copied. The iterator order is preserved.

## ◆ clear()

template<class T , class Allocator >
 void CGAL::Concurrent_compact_container< T, Allocator >::clear ( )

all items in ccc are deleted, and the memory is deallocated.

After this call, ccc is in the same state as if just default constructed.

## ◆ emplace()

template<class T , class Allocator >
template<class T1 >
 iterator CGAL::Concurrent_compact_container< T, Allocator >::emplace ( const T1 & t1 )

constructs an object of type T with the constructor that takes t1 as argument, inserts it in ccc, and returns the iterator pointing to it.

Overloads of this member function are defined that take additional arguments, up to 9.

## ◆ max_size()

template<class T , class Allocator >
 size_type CGAL::Concurrent_compact_container< T, Allocator >::max_size ( ) const

returns the maximum possible size of the container ccc.

This is the allocator's max_size value

## ◆ merge()

template<class T , class Allocator >
 void CGAL::Concurrent_compact_container< T, Allocator >::merge ( Concurrent_compact_container< T, Allocator > & ccc2 )

adds the items of ccc2 to the end of ccc and ccc2 becomes empty.

The time complexity is O(ccc.capacity()-ccc.size()).

Precondition
ccc2 must not be the same as ccc, and the allocators of ccc and ccc2 must be compatible: ccc.get_allocator() == ccc2.get_allocator().

## ◆ operator=()

template<class T , class Allocator >
 Concurrent_compact_container& CGAL::Concurrent_compact_container< T, Allocator >::operator= ( const Concurrent_compact_container< T, Allocator > & ccc2 )

assignment.

Each item in ccc2 is copied. The allocator is copied. Each item in ccc is deleted. The iterator order is preserved.

## ◆ size()

template<class T , class Allocator >
 size_type CGAL::Concurrent_compact_container< T, Allocator >::size ( ) const

returns the number of items in ccc.

Note: do not call this function while others are inserting/erasing elements

## ◆ swap()

template<class T , class Allocator >
 void CGAL::Concurrent_compact_container< T, Allocator >::swap ( Self & ccc2 )

swaps the contents of ccc and ccc2` in constant time complexity.

No exception is thrown.