Michael's hash set, RCU specialization. More...

#include <cds/intrusive/michael_set_rcu.h>

Public Types
typedef cds::urcu::gc< RCU >	gc
	RCU schema.

typedef OrderedList	ordered_list
	type of ordered list used as a bucket implementation

typedef Traits	traits
	Set traits.

typedef ordered_list::value_type	value_type
	type of value stored in the list

typedef ordered_list::key_comparator	key_comparator
	key comparing functor

typedef ordered_list::disposer	disposer
	Node disposer functor.

typedef ordered_list::stat	stat
	Internal statistics.

typedef cds::opt::v::hash_selector< typename traits::hash >::type	hash
	Hash functor for value_type and all its derivatives that you use.

typedef traits::item_counter	item_counter
	Item counter type.

typedef traits::allocator	allocator
	Bucket table allocator.

typedef ordered_list::rcu_lock	rcu_lock

typedef internal_bucket_type::exempt_ptr	exempt_ptr
	pointer to extracted node

typedef internal_bucket_type::raw_ptr	raw_ptr
	Return type of `get()` member function and its derivatives.

Public Member Functions
	MichaelHashSet (size_t nMaxItemCount, size_t nLoadFactor)
	Initialize hash set. More...

	~MichaelHashSet ()
	Clear hash set and destroy it.

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

template<typename Func >
bool	insert (value_type &val, Func f)
	Inserts new node. More...

template<typename Func >
std::pair< bool, bool >	update (value_type &val, Func func, bool bAllowInsert=true)
	Updates the element. More...

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

template<typename Q >
bool	erase (Q const &key)
	Deletes the item from the set. More...

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

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

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

template<typename Q >
exempt_ptr	extract (Q const &key)
	Extracts an item from the set. More...

template<typename Q , typename Less >
exempt_ptr	extract_with (Q const &key, Less pred)
	Extracts an item from the set using `pred` predicate for searching. More...

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

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

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

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

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

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

void	clear ()
	Clears the set (non-atomic) More...

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

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

size_t	bucket_count () const
	Returns the size of hash table. More...

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

Static Public Attributes
static constexpr const bool	c_bExtractLockExternal = ordered_list::c_bExtractLockExternal
	Group of `extract_xxx` functions require external locking if underlying ordered list requires that.

Forward iterators (thread-safe under RCU lock)
typedef michael_set::details::iterator< internal_bucket_type, false >	iterator
	Forward iterator. More...

typedef michael_set::details::iterator< internal_bucket_type, true >	const_iterator
	Const forward iterator. More...

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

iterator	end ()
	Returns an iterator that addresses the location succeeding the last element in a set. More...

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.

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

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

Detailed Description

template<class RCU, class OrderedList, class Traits = michael_set::traits>
class cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >

Michael's hash set, RCU specialization.

Source:

[2002] Maged Michael "High performance dynamic lock-free hash tables and list-based sets"

Michael's hash table algorithm is based on lock-free ordered list and it is very simple. The main structure is an array T of size M. Each element in T is basically a pointer to a hash bucket, implemented as a singly linked list. The array of buckets cannot be dynamically expanded. However, each bucket may contain unbounded number of items.

Template parameters are:

RCU - one of RCU type
OrderedList - ordered list implementation used as bucket for hash set, for example, MichaelList, LazyList. The intrusive ordered list implementation specifies the type T stored in the hash-set, the reclamation schema GC used by hash-set, the comparison functor for the type T and other features specific for the ordered list.
Traits - type traits, default is michael_set::traits. Instead of defining Traits struct you can use option-based syntax with michael_set::make_traits metafunction.

Usage: Before including <cds/intrusive/michael_set_rcu.h> you should include appropriate RCU header file, see RCU type for list of existing RCU class and corresponding header files. For example, for general-purpose buffered RCU you should include:
#include <cds/urcu/general_buffered.h>
#include <cds/intrusive/michael_list_rcu.h>
#include <cds/intrusive/michael_set_rcu.h>
struct Foo { ... };
// Hash functor for struct Foo
struct foo_hash {
size_t operator()( Foo const& foo ) const { return ... }
};
// Now, you can declare Michael's list for type Foo and default traits:
typedef cds::intrusive::MichaelList<cds::urcu::gc< general_buffered<> >, Foo > rcu_michael_list;
// Declare Michael's set with MichaelList as bucket type
typedef cds::intrusive::MichaelSet<
cds::urcu::gc< general_buffered<> >,
rcu_michael_list,
cds::intrusive::michael_set::make_traits<
cds::opt::::hash< foo_hash >
>::type
> rcu_michael_set;
// Declares hash set for 1000000 items with load factor 2
rcu_michael_set theSet( 1000000, 2 );
// Now you can use theSet object in many threads without any synchronization.

Member Typedef Documentation

◆ const_iterator

template<class RCU , class OrderedList , class Traits = michael_set::traits>

typedef michael_set::details::iterator< internal_bucket_type, true > cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::const_iterator

Const forward iterator.

For iterator's features and requirements see iterator

◆ iterator

template<class RCU , class OrderedList , class Traits = michael_set::traits>

typedef michael_set::details::iterator< internal_bucket_type, false > cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::iterator

Forward iterator.

The forward iterator for Michael's set is based on OrderedList forward iterator and has some features:

it has no post-increment operator
it iterates items in unordered fashion

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.

The iterator interface:

class iterator {
public:
    // Default constructor
    iterator();
    // Copy construtor
    iterator( iterator const& src );
    // Dereference operator
    value_type * operator ->() const;
    // Dereference operator
    value_type& operator *() const;
    // Preincrement operator
    iterator& operator ++();
    // Assignment operator
    iterator& operator = (iterator const& src);
    // Equality operators
    bool operator ==(iterator const& i ) const;
    bool operator !=(iterator const& i ) const;
};

◆ rcu_lock

template<class RCU , class OrderedList , class Traits = michael_set::traits>

typedef ordered_list::rcu_lock cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::rcu_lock

RCU scoped lock

Constructor & Destructor Documentation

◆ MichaelHashSet()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::MichaelHashSet	(	size_t	nMaxItemCount,
		size_t	nLoadFactor
	)

inline

Initialize hash set.

The Michael's hash set is an unbounded container, but its hash table is non-expandable. At construction time you should pass estimated maximum item count and a load factor. The load factor is average size of one bucket - a small number between 1 and 10. The bucket is an ordered single-linked list, the complexity of searching in the bucket is linear O(nLoadFactor). The constructor defines hash table size as rounding nMaxItemCount / nLoadFactor up to nearest power of two.

Parameters

nMaxItemCount	estimation of max item count in the hash set
nLoadFactor	load factor: average size of the bucket

Member Function Documentation

◆ begin()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

iterator cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::begin ( )

inline

Returns a forward iterator addressing the first element in a set.

For empty set

begin() == end()

◆ bucket_count()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

size_t cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::bucket_count ( ) const

inline

Returns the size of hash table.

Since MichaelHashSet cannot dynamically extend the hash table size, the value returned is an constant depending on object initialization parameters; see MichaelHashSet for explanation.

◆ clear()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

void cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::clear ( )

inline

Clears the set (non-atomic)

The function unlink all items from the set. The function is not atomic. It cleans up each bucket and then resets the item counter to zero. If there are a thread that performs insertion while clear is working the result is undefined in general case: empty() may return true but the set may contain item(s). Therefore, clear may be used only for debugging purposes.

For each item the disposer is called after unlinking.

◆ contains() [1/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::contains ( Q const & key )

inline

Checks whether the set contains key.

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

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.

◆ contains() [2/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Less >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::contains	(	Q const &	key,
		Less	pred
	)

inline

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

The function is an analog of 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.

◆ empty()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::empty ( ) const

inline

Checks if the set is empty.

Warning: If you use atomicity::empty_item_counter in traits::item_counter, the function always returns true.

◆ end()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

iterator cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::end ( )

inline

Returns an iterator that addresses the location succeeding the last element in a set.

Do not use the value returned by end function to access any item. The returned value can be used only to control reaching the end of the set. For empty set

begin() == end()

◆ erase() [1/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::erase ( Q const & key )

inline

Deletes the item from the set.

The function searches an item with key equal to key in the set, unlinks it from the set, and returns true. If the item with key equal to key is not found the function return false.

Note the hash functor should accept a parameter of type Q that may be not the same as value_type.

◆ erase() [2/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Func >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::erase	(	const Q &	key,
		Func	f
	)

inline

Deletes the item from the set.

The function searches an item with key equal to key in the set, call f functor with item found, and unlinks it from the set. The disposer specified in OrderedList class template parameter is called by garbage collector GC asynchronously.

The Func interface is

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

If the item with key equal to key is not found the function return false.

Note the hash functor should accept a parameter of type Q that can be not the same as value_type.

◆ erase_with() [1/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Less >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::erase_with	(	Q const &	key,
		Less	pred
	)

inline

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

The function is an analog of erase(Q const&) but pred is used for key comparing. Less functor has the interface like std::less. pred must imply the same element order as the comparator used for building the set.

◆ erase_with() [2/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Less , typename Func >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::erase_with	(	const Q &	key,
		Less	pred,
		Func	f
	)

inline

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

The function is an analog of erase(Q const&) but pred is used for key comparing. Less functor has the interface like std::less. pred must imply the same element order as the comparator used for building the set.

◆ extract()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q >

exempt_ptr cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::extract ( Q const & key )

inline

Extracts an item from the set.

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

Depends on ordered_list you should or should not lock RCU before calling of this function:

for the set based on MichaelList RCU should not be locked
for the set based on LazyList RCU should be locked

See ordered list implementation for details.

#include <cds/urcu/general_buffered.h>
#include <cds/intrusive/michael_list_rcu.h>
#include <cds/intrusive/michael_set_rcu.h>
typedef cds::urcu::gc< general_buffered<> > rcu;
typedef cds::intrusive::MichaelList< rcu, Foo > rcu_michael_list;
typedef cds::intrusive::MichaelHashSet< rcu, rcu_michael_list, foo_traits > rcu_michael_set;
rcu_michael_set theSet;
// ...
typename rcu_michael_set::exempt_ptr p;
// For MichaelList we should not lock RCU
// Now, you can apply extract function
// Note that you must not delete the item found inside the RCU lock
p = theSet.extract( 10 )
if ( p ) {
    // do something with p
    ...
}
// We may safely release p here
// release() passes the pointer to RCU reclamation cycle:
// it invokes RCU retire_ptr function with the disposer you provided for rcu_michael_list.
p.release();

◆ extract_with()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Less >

exempt_ptr cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::extract_with	(	Q const &	key,
		Less	pred
	)

inline

Extracts an item from the set using pred predicate for searching.

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

◆ find()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Func >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::find	(	Q &	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, Q& key );
};

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

The functor can change non-key fields of item. 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<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Less , typename Func >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::find_with	(	Q &	key,
		Less	pred,
		Func	f
	)

inline

Finds the key key using pred predicate for searching.

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

◆ get()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q >

raw_ptr cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::get ( Q const & key )

inline

Finds the key key and return the item found.

The function searches the item with key equal to key and returns the pointer to item found. If key is not found it returns nullptr. Note the type of returned value depends on underlying ordered_list. For details, see documentation of ordered list you use.

Note the compare functor should accept a parameter of type Q that can be not the same as value_type.

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

typedef cds::intrusive::MichaelHashSet< your_template_parameters > hash_set;
hash_set theSet;
// ...
// Result of get() call
typename hash_set::raw_ptr ptr;
{
    // Lock RCU
    hash_set::rcu_lock lock;
    ptr = theSet.get( 5 );
    if ( ptr ) {
        // Deal with ptr
        //...
    }
    // Unlock RCU by rcu_lock destructor
    // ptr can be reclaimed by disposer at any time after RCU has been unlocked
}

◆ get_with()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Q , typename Less >

raw_ptr cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::get_with	(	Q const &	key,
		Less	pred
	)

inline

Finds the key key and return the item found.

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

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

◆ insert() [1/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, 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.

◆ insert() [2/2]

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Func >

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::insert	(	value_type &	val,
		Func	f
	)

inline

Inserts new node.

This function is intended for derived non-intrusive containers.

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

create item with key only
insert new item into the set
if inserting is success, calls f functor to initialize value-field of val.

The functor signature is:

void func( value_type& val );

where val is the item inserted. The user-defined functor is called only if the inserting is success.

Warning: For MichaelList as the bucket see insert item troubleshooting. LazyList provides exclusive access to inserted item and does not require any node-level synchronization.

◆ size()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

size_t cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::size ( ) const

inline

Returns item count in the set.

If you use atomicity::empty_item_counter in traits::item_counter, the function always returns 0.

◆ unlink()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

bool cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::unlink ( value_type & val )

inline

Unlinks the item val from the set.

The function searches the item val in the set and unlink it from the set if it is found and is equal to val.

The function returns true if success and false otherwise.

◆ update()

template<class RCU , class OrderedList , class Traits = michael_set::traits>

template<typename Func >

std::pair<bool, bool> cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >::update	(	value_type &	val,
		Func	func,
		bool	bAllowInsert = `true`
	)

inline

Updates the element.

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

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

struct functor {
    void operator()( 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 refers to the same thing.

The functor may change non-key fields of the item.

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: For MichaelList as the bucket see insert item troubleshooting. LazyList provides exclusive access to inserted item and does not require any node-level synchronization.

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

cds/intrusive/michael_set_rcu.h

Public Types

Public Member Functions

Static Public Attributes

Forward iterators (thread-safe under RCU lock)

Detailed Description

template<class RCU, class OrderedList, class Traits = michael_set::traits> class cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >

Member Typedef Documentation

◆ const_iterator

◆ iterator

◆ rcu_lock

Constructor & Destructor Documentation

◆ MichaelHashSet()

Member Function Documentation

◆ begin()

◆ bucket_count()

◆ clear()

◆ contains() [1/2]

◆ contains() [2/2]

◆ empty()

◆ end()

◆ erase() [1/2]

◆ erase() [2/2]

◆ erase_with() [1/2]

◆ erase_with() [2/2]

◆ extract()

◆ extract_with()

◆ find()

◆ find_with()

◆ get()

◆ get_with()

◆ insert() [1/2]

◆ insert() [2/2]

◆ size()

◆ unlink()

◆ update()

template<class RCU, class OrderedList, class Traits = michael_set::traits>
class cds::intrusive::MichaelHashSet< cds::urcu::gc< RCU >, OrderedList, Traits >