cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits > Class Template Reference

Lock-free skip-list set (template specialization for gc::nogc) More...

#include <cds/intrusive/skip_list_nogc.h>

Inheritance diagram for cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >:

Public Types
typedef cds::gc::nogc	gc
	No garbage collector is used.
typedef T	value_type
	type of value stored in the skip-list
typedef Traits	traits
	Traits template parameter.
typedef traits::hook	hook
	hook type
typedef hook::node_type	node_type
	node type
typedef implementation_defined	key_comparator
	key comparison functor based on Traits::compare and Traits::less
typedef get_node_traits< value_type, node_type, hook >::type	node_traits
	node traits
typedef traits::item_counter	item_counter
	Item counting policy.
typedef traits::memory_model	memory_model
	Memory ordering. See cds::opt::memory_model option.
typedef traits::random_level_generator	random_level_generator
	random level generator
typedef traits::allocator	allocator_type
	allocator for maintaining array of next pointers of the node
typedef traits::back_off	back_off
	Back-off strategy.
typedef traits::stat	stat
	internal statistics type
typedef traits::disposer	disposer
	disposer

Public Member Functions
	SkipListSet ()
	Default constructor. More...
	~SkipListSet ()
	Clears and destructs the skip-list.
bool	insert (value_type &val)
	Inserts new node. More...
template<typename Func >
std::pair< bool, bool >	update (value_type &val, Func func, bool bInsert=true)
	Updates the node. More...
template<typename Q , typename Func >
bool	find (Q &key, Func f) const
	Finds key. More...
template<typename Q , typename Less , typename Func >
bool	find_with (Q &key, Less pred, Func f) const
	Finds the key key using pred predicate for comparing. More...
template<typename Q >
value_type *	contains (Q const &key) const
	Checks whether the set contains key. More...
template<typename Q , typename Less >
value_type *	contains (Q const &key, Less pred) const
	Checks whether the set contains key using pred predicate for searching. More...
value_type *	get_min () const
	Gets minimum key from the set. More...
value_type *	get_max () const
	Gets maximum key from the set. More...
void	clear ()
	Clears the set (non-atomic) More...
size_t	size () const
	Returns item count in the set. More...
bool	empty () const
	Checks if the set is empty.
stat const &	statistics () const
	Returns const reference to internal statistics.

Static Public Member Functions
static constexpr unsigned int	max_height () noexcept
	Returns maximum height of skip-list. The max height is a constant for each object and does not exceed 32.

Static Public Attributes
static unsigned int const	c_nMaxHeight
	Max node height. The actual node height should be in range [0 .. c_nMaxHeight) More...

Protected Types
typedef node_type::atomic_ptr	atomic_node_ptr
	Atomic node pointer.

Protected Attributes
head_node	m_Head
	head tower (max height)
random_level_generator	m_RandomLevelGen
	random level generator instance
atomics::atomic< unsigned int >	m_nHeight
	estimated high level
item_counter	m_ItemCounter
	item counter
stat	m_Stat
	internal statistics

Forward iterators
typedef skip_list::details::iterator< gc, node_traits, back_off, false >	iterator
	Forward iterator. More...
typedef skip_list::details::iterator< gc, node_traits, back_off, true >	const_iterator
	Const iterator type.
iterator	begin ()
	Returns a forward iterator addressing the first element in a set.
const_iterator	begin () const
	Returns a forward const iterator addressing the first element in a set.
const_iterator	cbegin () const
	Returns a forward const iterator addressing the first element in a set.
iterator	end ()
	Returns a forward iterator that addresses the location succeeding the last element in a set.
const_iterator	end () const
	Returns a forward const iterator that addresses the location succeeding the last element in a set.
const_iterator	cend () const
	Returns a forward const iterator that addresses the location succeeding the last element in a set.

Detailed Description

template<typename T, typename Traits = skip_list::traits>
class cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >

Lock-free skip-list set (template specialization for gc::nogc)

This specialization is so-called append-only when no item reclamation may be performed. The class does not support deleting of list item.

See SkipListSet for description of skip-list.

Template arguments :

• T - type to be stored in the set. The type must be based on skip_list::node (for skip_list::base_hook) or it must have a member of type skip_list::node (for skip_list::member_hook).
• Traits - type traits, default is skip_list::traits. It is possible to declare option-based list with cds::intrusive::skip_list::make_traits metafunction istead of Traits template argument.

Iterators

The class supports a forward iterator (iterator and const_iterator). The iteration is ordered.

The iterator class supports the following minimalistic interface:

struct iterator {
    // Default ctor
    iterator();

    // Copy ctor
    iterator( iterator const& s);

    value_type * operator ->() const;
    value_type& operator *() const;

    // Pre-increment
    iterator& operator ++();

    // Copy assignment
    iterator& operator = (const iterator& src);

    bool operator ==(iterator const& i ) const;
    bool operator !=(iterator const& i ) const;
};

Note, the iterator object returned by end, cend member functions points to nullptr and should not be dereferenced.

How to use

You should incorporate skip_list::node into your struct T and provide appropriate skip_list::traits::hook in your Traits template parameters. Usually, for Traits you define a struct based on skip_list::traits.

Example for base hook:

#include <cds/intrusive/skip_list_nogc.h>

// Data stored in skip list
struct my_data: public cds::intrusive::skip_list::node< cds::gc::nogc >
{
    // key field
    std::string     strKey;

    // other data
    // ...
};

// my_data compare functor
struct my_data_cmp {
    int operator()( const my_data& d1, const my_data& d2 )
    {
        return d1.strKey.compare( d2.strKey );
    }

    int operator()( const my_data& d, const std::string& s )
    {
        return d.strKey.compare(s);
    }

    int operator()( const std::string& s, const my_data& d )
    {
        return s.compare( d.strKey );
    }
};


// Declare traits
struct my_traits: public cds::intrusive::skip_list::traits
{
    typedef cds::intrusive::skip_list::base_hook< cds::opt::gc< cds::gc::nogc > > hook;
    typedef my_data_cmp compare;
};

// Declare skip-list set type
typedef cds::intrusive::SkipListSet< cds::gc::nogc, my_data, my_traits > traits_based_set;

Equivalent option-based code:

// GC-related specialization
#include <cds/intrusive/skip_list_nogc.h>

struct my_data {
    // see above
};
struct compare {
    // see above
};

// Declare option-based skip-list set
typedef cds::intrusive::SkipListSet< cds::gc::nogc
    ,my_data
    , typename cds::intrusive::skip_list::make_traits<
        cds::intrusive::opt::hook< cds::intrusive::skip_list::base_hook< cds::opt::gc< cds::gc::nogc > > >
        ,cds::intrusive::opt::compare< my_data_cmp >
    >::type
> option_based_set;

Member Typedef Documentation

iterator

template<typename T , typename Traits = skip_list::traits>

typedef skip_list::details::iterator< gc, node_traits, back_off, false > cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::iterator

Forward iterator.

The forward iterator for a split-list has some features:

• it has no post-increment operator
• it depends on iterator of underlying OrderedList

Constructor & Destructor Documentation

SkipListSet()

template<typename T , typename Traits = skip_list::traits>

cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::SkipListSet ( )

inline

Default constructor.

The constructor checks whether the count of guards is enough for skip-list and may raise an exception if not.

Member Function Documentation

clear()

template<typename T , typename Traits = skip_list::traits>

void cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::clear ( )

inline

Clears the set (non-atomic)

The function is not atomic. Finding and/or inserting is prohibited while clearing. Otherwise an unpredictable result may be encountered. Thus, clear() may be used only for debugging purposes.

contains() [1/2]

template<typename T , typename Traits = skip_list::traits>

template<typename Q >

value_type* cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::contains ( Q const &  key ) const

inline

Checks whether the set contains key.

The function searches the item with key equal to key and returns pointer to item found or nullptr.

contains() [2/2]

template<typename T , typename Traits = skip_list::traits>

template<typename Q , typename Less >

value_type* cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::contains ( Q const &  key, Less  pred  ) const

inline

Checks whether the set contains key using pred predicate for searching.

The function is similar to contains( key ) but pred is used for key comparing. Less functor has the interface like std::less. Less must imply the same element order as the comparator used for building the set.

find()

template<typename T , typename Traits = skip_list::traits>

template<typename Q , typename Func >

bool cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::find ( Q &  key, Func  f  ) const

inline

Finds key.

The function searches the item with key equal to key and calls the functor f for item found. The interface of Func functor is:

struct functor {
    void operator()( value_type& item, Q& key );
};

where item is the item found, key is the find function argument.

The functor can change non-key fields of item. Note that the functor is only guarantee that item cannot be disposed during functor is executing. The functor does not serialize simultaneous access to the set item. If such access is possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.

The key argument is non-const since it can be used as f functor destination i.e., the functor can modify both arguments.

Note the hash functor specified for class Traits template parameter should accept a parameter of type Q that can be not the same as value_type.

The function returns true if key is found, false otherwise.

find_with()

template<typename T , typename Traits = skip_list::traits>

template<typename Q , typename Less , typename Func >

bool cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::find_with ( Q &  key, Less  pred, Func  f  ) const

inline

Finds the key key using pred predicate for comparing.

The function is an analog of find(Q&, Func) but pred predicate is used for key compare. Less has the interface like std::less. pred must imply the same element order as the comparator used for building the set.

get_max()

template<typename T , typename Traits = skip_list::traits>

value_type* cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::get_max ( ) const

inline

Gets maximum key from the set.

The function returns nullptr if the set is empty

get_min()

template<typename T , typename Traits = skip_list::traits>

value_type* cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::get_min ( ) const

inline

Gets minimum key from the set.

If the set is empty the function returns nullptr

insert()

template<typename T , typename Traits = skip_list::traits>

bool cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::insert ( value_type &  val )

inline

Inserts new node.

The function inserts val in the set if it does not contain an item with key equal to val.

Returns true if val is placed into the set, false otherwise.

size()

template<typename T , typename Traits = skip_list::traits>

size_t cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::size ( ) const

inline

Returns item count in the set.

The value returned depends on item counter type provided by Traits template parameter. For atomicity::empty_item_counter the function always returns 0. The function is not suitable for checking the set emptiness, use empty().

update()

template<typename T , typename Traits = skip_list::traits>

template<typename Func >

std::pair<bool, bool> cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::update ( value_type &  val, Func  func, bool  bInsert = true  )

inline

Updates the node.

The operation performs inserting or changing data with lock-free manner.

If the item val is not found in the set, then val is inserted into the set iff bInsert is true. Otherwise, the functor func is called with item found. The functor signature is:

void func( bool bNew, value_type& item, value_type& val );

with arguments:

• bNew - true if the item has been inserted, false otherwise
• item - item of the set
• val - argument val passed into the update() function If new item has been inserted (i.e. bNew is true) then item and val arguments refer to the same thing.

The functor can change non-key fields of the item; however, func must guarantee that during changing no any other modifications could be made on this item by concurrent threads.

Returns std::pair<bool, bool> where first is true if operation is successful, second is true if new item has been added or false if the item with key already is in the set.

Warning

See insert item troubleshooting

Field Documentation

c_nMaxHeight

template<typename T , typename Traits = skip_list::traits>

unsigned int const cds::intrusive::SkipListSet< cds::gc::nogc, T, Traits >::c_nMaxHeight

static

Initial value:

= std::conditional<
            (random_level_generator::c_nUpperBound <= skip_list::c_nHeightLimit),
            std::integral_constant< unsigned int, random_level_generator::c_nUpperBound >,
            std::integral_constant< unsigned int, skip_list::c_nHeightLimit >
        >::type::value

Max node height. The actual node height should be in range [0 .. c_nMaxHeight)

The max height is specified by random level generator constant m_nUpperBound but it should be no more than 32 (skip_list::c_nHeightLimit).

---

The documentation for this class was generated from the following file:

• cds/intrusive/skip_list_nogc.h