Lock-free skip-list map (template specialization for RCU) More...

#include <cds/container/skip_list_map_rcu.h>

Inheritance diagram for cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >:

Public Types
typedef cds::urcu::gc< RCU >	gc
	Garbage collector used.

typedef Key	key_type
	Key type.

typedef T	mapped_type
	Mapped type.

typedef std::pair< K const, T >	value_type
	Value type stored in the map.

typedef Traits	traits
	Map traits.

typedef base_class::back_off	back_off
	Back-off strategy used.

typedef traits::allocator	allocator_type
	Allocator type used for allocate/deallocate the skip-list nodes.

typedef base_class::item_counter	item_counter
	Item counting policy used.

typedef maker::key_comparator	key_comparator
	key comparison functor

typedef base_class::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::stat	stat
	internal statistics type

typedef base_class::rcu_lock	rcu_lock

using	exempt_ptr = cds::urcu::exempt_ptr< gc, node_type, value_type, typename maker::intrusive_type_traits::disposer >
	pointer to extracted node

typedef cds::urcu::raw_ptr_adaptor< value_type, typename base_class::raw_ptr, raw_ptr_converter >	raw_ptr
	Result of `get()`, `get_with()` functions - pointer to the node found.

Public Member Functions
	SkipListMap ()
	Default ctor.

	~SkipListMap ()
	Destructor destroys the set object.

template<typename K >
bool	insert (K const &key)
	Inserts new node with key and default value. More...

template<typename K , typename V >
bool	insert (K const &key, V const &val)
	Inserts new node. More...

template<typename K , typename Func >
bool	insert_with (const K &key, Func func)
	Inserts new node and initialize it by a functor. More...

template<typename K , typename... Args>
bool	emplace (K &&key, Args &&...args)
	For key `key` inserts data of type `value_type` created in-place from `args`. More...

template<typename K , typename Func >
std::pair< bool, bool >	update (K const &key, Func func, bool bInsert=true)
	Updates data by `key`. More...

template<typename K >
bool	erase (K const &key)
	Delete `key` from the map. More...

template<typename K , typename Less >
bool	erase_with (K const &key, Less pred)
	Deletes the item from the map using `pred` predicate for searching. More...

template<typename K , typename Func >
bool	erase (K const &key, Func f)
	Delete `key` from the map. More...

template<typename K , typename Less , typename Func >
bool	erase_with (K const &key, Less pred, Func f)
	Deletes the item from the map using `pred` predicate for searching. More...

template<typename K >
exempt_ptr	extract (K const &key)
	Extracts the item from the map with specified `key`. More...

template<typename K , typename Less >
exempt_ptr	extract_with (K const &key, Less pred)
	Extracts the item from the map with comparing functor `pred`. More...

exempt_ptr	extract_min ()
	Extracts an item with minimal key from the map. More...

exempt_ptr	extract_max ()
	Extracts an item with maximal key from the map. More...

template<typename K , typename Func >
bool	find (K const &key, Func f)
	Find the key `key`. More...

template<typename K , typename Less , typename Func >
bool	find_with (K const &key, Less pred, Func f)
	Finds the key `val` using `pred` predicate for searching. More...

template<typename K >
bool	contains (K const &key)
	Checks whether the map contains `key`. More...

template<typename K , typename Less >
bool	contains (K const &key, Less pred)
	Checks whether the map contains `key` using `pred` predicate for searching. More...

template<typename K >
raw_ptr	get (K const &key)
	Finds the key `key` and return the item found. More...

template<typename K , typename Less >
raw_ptr	get_with (K const &key, Less pred)
	Finds the key `key` and return the item found. More...

void	clear ()
	Clears the map (not atomic)

bool	empty () const
	Checks if the map is empty. More...

size_t	size () const
	Returns item count in the map.

stat const &	statistics () const
	Returns const reference to internal statistics.

Static Public Attributes
static constexpr const bool	c_bExtractLockExternal = base_class::c_bExtractLockExternal
	Group of `extract_xxx` functions do not require external locking.

Forward ordered iterators (thread-safe under RCU lock)
typedef skip_list::details::iterator< typename base_class::iterator >	iterator
	Forward iterator. More...

typedef skip_list::details::iterator< typename base_class::const_iterator >	const_iterator
	Const iterator type.

iterator	begin ()
	Returns a forward iterator addressing the first element in a map.

const_iterator	begin () const
	Returns a forward const iterator addressing the first element in a map.

const_iterator	cbegin () const
	Returns a forward const iterator addressing the first element in a map.

iterator	end ()
	Returns a forward iterator that addresses the location succeeding the last element in a map.

const_iterator	end () const
	Returns a forward const iterator that addresses the location succeeding the last element in a map.

const_iterator	cend () const
	Returns a forward const iterator that addresses the location succeeding the last element in a map.

Additional Inherited Members
Protected Types inherited from cds::intrusive::SkipListSet< cds::urcu::gc< RCU >, std::pair< Key const, T >, Traits >
typedef node_type::atomic_marked_ptr	atomic_node_ptr
	Atomic marked node pointer.

typedef node_type::marked_ptr	marked_node_ptr
	Node marked pointer.

typedef cds::urcu::gc< RCU >	gc
	Garbage collector.

typedef std::pair< Key const, 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 opt::compare and opt::less option setter.

typedef traits::disposer	disposer
	item disposer

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 gc::template guarded_ptr< value_type >	guarded_ptr
	Guarded pointer.

typedef skip_list::details::iterator< gc, node_traits, back_off, false >	iterator
	Iterator type. More...

typedef skip_list::details::iterator< gc, node_traits, back_off, true >	const_iterator
	Const iterator type.

Protected Member Functions inherited from cds::intrusive::SkipListSet< cds::urcu::gc< RCU >, std::pair< Key const, T >, Traits >
	SkipListSet ()
	Default constructor. More...

	~SkipListSet ()
	Clears and destructs the skip-list.

bool	insert (value_type &val)
	Inserts new node. More...

bool	insert (value_type &val, Func f)
	Inserts new node. More...

std::pair< bool, bool >	update (value_type &val, Func func, bool bInsert=true)
	Updates the node. More...

bool	unlink (value_type &val)
	Unlinks the item `val` from the set. More...

guarded_ptr	extract (Q const &key)
	Extracts the item from the set with specified `key`. More...

guarded_ptr	extract_with (Q const &key, Less pred)
	Extracts the item from the set with comparing functor `pred`. More...

guarded_ptr	extract_min ()
	Extracts an item with minimal key from the list. More...

guarded_ptr	extract_max ()
	Extracts an item with maximal key from the list. More...

bool	erase (Q const &key)
	Deletes the item from the set. More...

bool	erase (Q const &key, Func f)
	Deletes the item from the set. More...

bool	erase_with (Q const &key, Less pred)
	Deletes the item from the set with comparing functor `pred`. More...

bool	erase_with (Q const &key, Less pred, Func f)
	Deletes the item from the set with comparing functor `pred`. More...

bool	find (Q &key, Func f)
	Finds `key`. More...

bool	find_with (Q &key, Less pred, Func f)
	Finds the key `key` with `pred` predicate for comparing. More...

bool	contains (Q const &key)
	Checks whether the set contains `key`. More...

bool	contains (Q const &key, Less pred)
	Checks whether the set contains `key` using `pred` predicate for searching. More...

guarded_ptr	get (Q const &key)
	Finds `key` and return the item found. More...

guarded_ptr	get_with (Q const &key, Less pred)
	Finds `key` and return the item found. More...

size_t	size () const
	Returns item count in the set. More...

bool	empty () const
	Checks if the set is empty.

void	clear ()
	Clears the set (not atomic) More...

stat const &	statistics () const
	Returns const reference to internal statistics.

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.

Static Protected Member Functions inherited from cds::intrusive::SkipListSet< cds::urcu::gc< RCU >, std::pair< Key const, T >, Traits >
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 Protected Attributes inherited from cds::intrusive::SkipListSet< cds::urcu::gc< RCU >, std::pair< Key const, T >, Traits >
static unsigned int const	c_nMaxHeight
	Max node height. The actual node height should be in range `[0 .. c_nMaxHeight)` More...

static size_t const	c_nHazardPtrCount
	Count of hazard pointer required for the skip-list.

Detailed Description

template<typename RCU, typename Key, typename T, typename Traits = skip_list::traits>
class cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >

Lock-free skip-list map (template specialization for RCU)

The implementation of well-known probabilistic data structure called skip-list invented by W.Pugh in his papers:

[1989] W.Pugh Skip Lists: A Probabilistic Alternative to Balanced Trees
[1990] W.Pugh A Skip List Cookbook

A skip-list is a probabilistic data structure that provides expected logarithmic time search without the need of rebalance. The skip-list is a collection of sorted linked list. Nodes are ordered by key. Each node is linked into a subset of the lists. Each list has a level, ranging from 0 to 32. The bottom-level list contains all the nodes, and each higher-level list is a sublist of the lower-level lists. Each node is created with a random top level (with a random height), and belongs to all lists up to that level. The probability that a node has the height 1 is 1/2. The probability that a node has the height N is 1/2 ** N (more precisely, the distribution depends on an random generator provided, but our generators have this property).

The lock-free variant of skip-list is implemented according to book

[2008] M.Herlihy, N.Shavit "The Art of Multiprocessor Programming", chapter 14.4 "A Lock-Free Concurrent Skiplist"

Template arguments:

RCU - one of RCU type.
K - type of a key to be stored in the list.
T - type of a value to be stored in the list.
Traits - map traits, default is skip_list::traits. It is possible to declare option-based list with cds::container::skip_list::make_traits metafunction instead of Traits template argument.

Like STL map class, SkipListMap stores its key-value pair as std:pair< K const, T>.

Note: Before including <cds/container/skip_list_map_rcu.h> you should include appropriate RCU header file, see RCU type for list of existing RCU class and corresponding header files.

Iterators

The class supports a forward iterator (iterator and const_iterator). The iteration is ordered. You may iterate over skip-list set items only under RCU lock. Only in this case the iterator is thread-safe since while RCU is locked any set's item cannot be reclaimed.

The requirement of RCU lock during iterating means that deletion of the elements (i.e. erase) is not possible.

Warning: The iterator object cannot be passed between threads

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.

Member Typedef Documentation

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

typedef skip_list::details::iterator< typename base_class::iterator > cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::iterator

Forward iterator.

The forward iterator has some features:

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

You may safely use iterators in multi-threaded environment only under RCU lock. Otherwise, a crash is possible if another thread deletes the element the iterator points to.

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

typedef base_class::rcu_lock cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::rcu_lock

RCU scoped lock

Member Function Documentation

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

template<typename K >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::contains ( K const & key )

inline

Checks whether the map contains key.

The function searches the item with key equal to key and returns true if it is found, and false otherwise.

The function applies RCU lock internally.

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

template<typename K , typename Less >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::contains	(	K const &	key,
		Less	pred
	)

inline

Checks whether the map 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.

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

template<typename K , typename... Args>

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::emplace	(	K &&	key,
		Args &&...	args
	)

inline

For key key inserts data of type value_type created in-place from args.

Returns true if inserting successful, false otherwise.

RCU synchronize() method can be called. RCU should not be locked.

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

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::empty ( ) const

inline

Checks if the map is empty.

Emptiness is checked by item counting: if item count is zero then the map is empty.

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

template<typename K >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::erase ( K const & key )

inline

Delete key from the map.

RCU synchronize method can be called. RCU should not be locked.

Return true if key is found and deleted, false otherwise

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

template<typename K , typename Func >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::erase	(	K const &	key,
		Func	f
	)

inline

Delete key from the map.

The function searches an item with key key, calls f functor and deletes the item. If key is not found, the functor is not called.

The functor Func interface:

struct extractor {
    void operator()(value_type& item) { ... }
};

RCU synchronize method can be called. RCU should not be locked.

Return true if key is found and deleted, false otherwise

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

template<typename K , typename Less >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::erase_with	(	K const &	key,
		Less	pred
	)

inline

Deletes the item from the map using pred predicate for searching.

The function is an analog of erase(K const&) 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 map.

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

template<typename K , typename Less , typename Func >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::erase_with	(	K const &	key,
		Less	pred,
		Func	f
	)

inline

Deletes the item from the map using pred predicate for searching.

The function is an analog of erase(K const&, Func) 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 map.

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

template<typename K >

exempt_ptr cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::extract ( K const & key )

inline

Extracts the item from the map with specified key.

The function searches an item with key equal to key in the map, unlinks it from the set, and returns exempt_ptr pointer to the item found. If the item is not found the function returns an empty exempt_ptr

Note the compare functor from Traits class' template argument should accept a parameter of type K that can be not the same as key_type.

RCU synchronize() method can be called. RCU should NOT be locked.

The function does not free the item found. The item will be implicitly freed when the returned object is destroyed or when its release() member function is called.

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

exempt_ptr cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::extract_max ( )

inline

Extracts an item with maximal key from the map.

The function searches an item with maximal key, unlinks it from the set, and returns exempt_ptr pointer to the item. If the skip-list is empty the function returns an empty exempt_ptr.

RCU synchronize method can be called. RCU should NOT be locked.

The function does not free the item found. The item will be implicitly freed when the returned object is destroyed or when its release() member function is called.

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

exempt_ptr cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::extract_min ( )

inline

Extracts an item with minimal key from the map.

The function searches an item with minimal key, unlinks it, and returns exempt_ptr pointer to the item. If the skip-list is empty the function returns an empty exempt_ptr.

RCU synchronize method can be called. RCU should NOT be locked.

The function does not free the item found. The item will be implicitly freed when the returned object is destroyed or when its release() member function is called.

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

template<typename K , typename Less >

exempt_ptr cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::extract_with	(	K const &	key,
		Less	pred
	)

inline

Extracts the item from the map with comparing functor pred.

The function is an analog of extract(K const&) but pred predicate is used for key comparing. Less has the semantics like std::less. pred must imply the same element order as the comparator used for building the map.

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

template<typename K , typename Func >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::find	(	K const &	key,
		Func	f
	)

inline

Find the key 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 );
};

where item is the item found.

The functor may change item.second.

The function applies RCU lock internally.

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

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

template<typename K , typename Less , typename Func >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::find_with	(	K const &	key,
		Less	pred,
		Func	f
	)

inline

Finds the key val using pred predicate for searching.

The function is an analog of find(K const&, Func) 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 map.

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

template<typename K >

raw_ptr cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::get ( K const & key )

inline

Finds the key key and return the item found.

The function searches the item with key equal to key and returns a raw_ptr object pointing to an item found. If key is not found it returns empty raw_ptr.

Note the compare functor in Traits class' template argument should accept a parameter of type K that can be not the same as key_type.

RCU should be locked before call of this function. Returned item is valid only while RCU is locked:

typedef cds::container::SkipListMap< cds::urcu::gc< cds::urcu::general_buffered<> >, int, foo, my_traits > skip_list;
skip_list theList;
// ...
typename skip_list::raw_ptr pVal;
{
    // Lock RCU
    skip_list::rcu_lock lock;
    pVal = theList.get( 5 );
    if ( pVal ) {
        // Deal with pVal
        //...
    }
}
// You can manually release pVal after RCU-locked section
pVal.release();

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

template<typename K , typename Less >

raw_ptr cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::get_with	(	K const &	key,
		Less	pred
	)

inline

Finds the key key and return the item found.

The function is an analog of get(K const&) but pred is used for comparing the keys.

Less functor has the semantics like std::less but should take arguments of type key_type and K in any order. pred must imply the same element order as the comparator used for building the map.

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

template<typename K >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::insert ( K const & key )

inline

Inserts new node with key and default value.

The function creates a node with key and default value, and then inserts the node created into the map.

Preconditions:

The key_type should be constructible from a value of type K. In trivial case, K is equal to key_type.
The mapped_type should be default-constructible.

RCU synchronize method can be called. RCU should not be locked.

Returns true if inserting successful, false otherwise.

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

template<typename K , typename V >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::insert	(	K const &	key,
		V const &	val
	)

inline

Inserts new node.

The function creates a node with copy of val value and then inserts the node created into the map.

Preconditions:

The key_type should be constructible from key of type K.
The value_type should be constructible from val of type V.

RCU synchronize method can be called. RCU should not be locked.

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

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

template<typename K , typename Func >

bool cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::insert_with	(	const K &	key,
		Func	func
	)

inline

Inserts new node and initialize it by a functor.

This function inserts new node with key key and if inserting is successful then it calls func functor with signature

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

The argument item of user-defined functor func is the reference to the map's item inserted:

item.first is a const reference to item's key that cannot be changed.
item.second is a reference to item's value that may be changed.

The function allows to split creating of new item into three part:

create item from key;
insert new item into the map;
if inserting is successful, initialize the value of item by calling func functor

This can be useful if complete initialization of object of value_type is heavyweight and it is preferable that the initialization should be completed only if inserting is successful.

RCU synchronize method can be called. RCU should not be locked.

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

template<typename K , typename Func >

std::pair<bool, bool> cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >::update	(	K const &	key,
		Func	func,
		bool	bInsert = `true`
	)

inline

Updates data by key.

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

If the key not found in the map, then the new item created from key is inserted into the map iff bInsert is true. Otherwise, if key found, the functor func is called with item found. The functor Func interface is:

struct my_functor {
    void operator()( bool bNew, value_type& item );
};

where:

bNew - true if the item has been inserted, false otherwise
item - item of the map

The functor may change any fields of item.second.

RCU synchronize() method can be called. RCU should not be locked.

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 exists.

Warning: See insert item troubleshooting

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

cds/container/skip_list_map_rcu.h

Public Types

Public Member Functions

Static Public Attributes

Forward ordered iterators (thread-safe under RCU lock)

Additional Inherited Members

Detailed Description

template<typename RCU, typename Key, typename T, typename Traits = skip_list::traits> class cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >

Member Typedef Documentation

Member Function Documentation

template<typename RCU, typename Key, typename T, typename Traits = skip_list::traits>
class cds::container::SkipListMap< cds::urcu::gc< RCU >, Key, T, Traits >