Michael's hash set. More...

#include <cds/intrusive/michael_set.h>

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

typedef ordered_list	bucket_type
	bucket type

typedef Traits	options
	Traits template parameters.

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

typedef GC	gc
	Garbage collector.

typedef ordered_list::key_comparator	key_comparator
	key comparision functor

typedef ordered_list::disposer	disposer
	Node disposer functor.

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

typedef options::item_counter	item_counter
	Item counter type.

typedef cds::details::Allocator < bucket_type, typename options::allocator >	bucket_table_allocator
	Bucket table allocator.

typedef michael_set::details::iterator < bucket_type, false >	iterator
	Forward iterator. More...

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

Public Member Functions
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...

	MichaelHashSet (size_t nMaxItemCount, size_t nLoadFactor)
	Initializes hash set. More...

	~MichaelHashSet ()
	Clears hash set object and destroys 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 >	ensure (value_type &val, Func func)
	Ensures that the `val` exists in the set. More...

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

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

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

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

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

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

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

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

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

template<typename Q >
bool	find (Q const &val)
	Finds the key `val`. More...

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

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


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

const_iterator	cbegin ()


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

const_iterator	cend ()

Protected Member Functions
template<typename Q >
size_t	hash_value (const Q &key) const
	Calculates hash value of `key`.

template<typename Q >
bucket_type &	bucket (const Q &key)
	Returns the bucket (ordered list) for `key`.

Protected Attributes
item_counter	m_ItemCounter
	Item counter.

hash	m_HashFunctor
	Hash functor.

bucket_type *	m_Buckets
	bucket table

Private Member Functions

const_iterator	get_const_begin () const

const_iterator	get_const_end () const

Detailed Description

template<class GC, class OrderedList, class Traits = michael_set::type_traits>
class cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >

Michael's hash set.

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:

GC - Garbage collector used. Note the GC must be the same as the GC used for OrderedList
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. See michael_set::type_traits for explanation. Instead of defining Traits struct you can use option-based syntax with michael_set::make_traits metafunction.

There are several specializations of MichaelHashSet for each GC. You should include:

<cds/intrusive/michael_set_rcu.h> for RCU type
<cds/intrusive/michael_set_nogc.h> for cds_intrusive_MichaelHashSet_nogc for persistent set
<cds/intrusive/michael_set.h> for other GC (gc::HP, gc::HRC, gc::PTB)

Hash functor

Some member functions of Michael's hash set accept the key parameter of type Q which differs from value_type. It is expected that type Q contains full key of value_type, and for equal keys of type Q and value_type the hash values of these keys must be equal too. The hash functor Traits::hash should accept parameters of both type:

// Our node type
struct Foo {
    std::string     key_    ;   // key field
    // ... other fields
}   ;
// Hash functor
struct fooHash {
    size_t operator()( const std::string& s ) const
    {
        return std::hash( s )   ;
    }
    size_t operator()( const Foo& f ) const
    {
        return (*this)( f.key_ )    ;
    }
};

How to use

First, you should define ordered list type to use in your hash set:

// For gc::HP-based MichaelList implementation
#include <cds/intrusive/michael_list_hp.h>
// cds::intrusive::MichaelHashSet declaration
#include <cds/intrusive/michael_set.h>
// Type of hash-set items
struct Foo: public cds::intrusive::michael_list::node< cds::gc::HP >
{
    std::string     key_    ;   // key field
    unsigned        val_    ;   // value field
    // ...  other value fields
};
// Declare comparator for the item
struct FooCmp
{
    int operator()( const Foo& f1, const Foo& f2 ) const
    {
        return f1.key_.compare( f2.key_ ) ;
    }
};
// Declare bucket type for Michael's hash set
// The bucket type is any ordered list type like MichaelList, LazyList
typedef cds::intrusive::MichaelList< cds::gc::HP, Foo,
    typename cds::intrusive::michael_list::make_traits<
        // hook option
        cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::HP > > >
        // item comparator option
        ,cds::opt::compare< FooCmp >
    >::type
>  Foo_bucket   ;

Second, you should declare Michael's hash set container:

// Declare hash functor
// Note, the hash functor accepts parameter type Foo and std::string
struct FooHash {
    size_t operator()( const Foo& f ) const
    {
        return cds::opt::v::hash<std::string>()( f.key_ ) ;
    }
    size_t operator()( const std::string& f ) const
    {
        return cds::opt::v::hash<std::string>()( f ) ;
    }
};
// Michael's set typedef
typedef cds::intrusive::MichaelHashSet<
    cds::gc::HP
    ,Foo_bucket
    ,typename cds::intrusive::michael_set::make_traits<
        cds::opt::hash< FooHash >
    >::type
> Foo_set   ;

Now, you can use Foo_set in your application.

Like other intrusive containers, you may build several containers on single item structure:

#include <cds/intrusive/michael_list_hp.h>
#include <cds/intrusive/michael_list_ptb.h>
#include <cds/intrusive/michael_set.h>
struct tag_key1_idx ;
struct tag_key2_idx ;
// Your two-key data
// The first key is maintained by gc::HP, second key is maintained by gc::PTB garbage collectors
struct Foo
    : public cds::intrusive::michael_list::node< cds::gc::HP, tag_key1_idx >
    , public cds::intrusive::michael_list::node< cds::gc::PTB, tag_key2_idx >
{
    std::string     key1_   ;   // first key field
    unsigned int    key2_   ;   // second key field
    // ... value fields and fields for controlling item's lifetime
};
// Declare comparators for the item
struct Key1Cmp
{
    int operator()( const Foo& f1, const Foo& f2 ) const { return f1.key1_.compare( f2.key1_ ) ; }
};
struct Key2Less
{
    bool operator()( const Foo& f1, const Foo& f2 ) const { return f1.key2_ < f2.key1_ ; }
};
// Declare bucket type for Michael's hash set indexed by key1_ field and maintained by gc::HP
typedef cds::intrusive::MichaelList< cds::gc::HP, Foo,
    typename cds::intrusive::michael_list::make_traits<
        // hook option
        cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::HP >, tag_key1_idx > >
        // item comparator option
        ,cds::opt::compare< Key1Cmp >
    >::type
>  Key1_bucket   ;
// Declare bucket type for Michael's hash set indexed by key2_ field and maintained by gc::PTB
typedef cds::intrusive::MichaelList< cds::gc::PTB, Foo,
    typename cds::intrusive::michael_list::make_traits<
        // hook option
        cds::intrusive::opt::hook< cds::intrusive::michael_list::base_hook< cds::opt::gc< cds::gc::PTB >, tag_key2_idx > >
        // item comparator option
        ,cds::opt::less< Key2Less >
    >::type
>  Key2_bucket   ;
// Declare hash functor
struct Key1Hash {
    size_t operator()( const Foo& f ) const { return cds::opt::v::hash<std::string>()( f.key1_ ) ; }
    size_t operator()( const std::string& s ) const { return cds::opt::v::hash<std::string>()( s ) ; }
};
inline size_t Key2Hash( const Foo& f ) { return (size_t) f.key2_  ; }
// Michael's set indexed by key1_ field
typedef cds::intrusive::MichaelHashSet<
    cds::gc::HP
    ,Key1_bucket
    ,typename cds::intrusive::michael_set::make_traits<
        cds::opt::hash< Key1Hash >
    >::type
> key1_set   ;
// Michael's set indexed by key2_ field
typedef cds::intrusive::MichaelHashSet<
    cds::gc::PTB
    ,Key2_bucket
    ,typename cds::intrusive::michael_set::make_traits<
        cds::opt::hash< Key2Hash >
    >::type
> key2_set   ;

Member Typedef Documentation

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

typedef michael_set::details::iterator< bucket_type, true > cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::const_iterator

Const forward iterator.

For iterator's features and requirements see iterator

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

typedef michael_set::details::iterator< bucket_type, false > cds::intrusive::MichaelHashSet< GC, 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
The iterator cannot be moved across thread boundary since it may contain GC's guard that is thread-private GC data.
Iterator ensures thread-safety even if you delete the item that iterator points to. However, in case of concurrent deleting operations it is no guarantee that you iterate all item in the set.

Therefore, the use of iterators in concurrent environment is not good idea. Use the iterator for the concurrent container for debug purpose only.

Constructor & Destructor Documentation

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::MichaelHashSet	(	size_t	nMaxItemCount,
		size_t	nLoadFactor
	)

inline

Initializes hash set.

The Michael's hash set is non-expandable container. You should point the average count of items nMaxItemCount when you create an object. nLoadFactor parameter defines average count of items per bucket and it should be small number between 1 and 10. Remember, since the bucket implementation is an ordered list, searching in the bucket is linear [O(nLoadFactor)]. Note, that many popular STL hash map implementation uses load factor 1.

The ctor defines hash table size as rounding nMacItemCount / nLoadFactor up to nearest power of two.

Parameters

nMaxItemCount	estimation of max item count in the hash set
nLoadFactor	load factor: estimation of max number of items in the bucket. Small integer up to 10, default is 1.

Member Function Documentation

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

iterator cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::begin ( )

inline

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

For empty set

begin() == end()

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

size_t cds::intrusive::MichaelHashSet< GC, 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::MichaelHashSet for explanation.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

void cds::intrusive::MichaelHashSet< GC, 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::empty ( ) const

inline

Checks if the set is empty.

Emptiness is checked by item counting: if item count is zero then the set is empty. Thus, the correct item counting feature is an important part of Michael's set implementation.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

iterator cds::intrusive::MichaelHashSet< GC, 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()

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Func >

std::pair<bool, bool> cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::ensure	(	value_type &	val,
		Func	func
	)

inline

Ensures that the val exists in the set.

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

If the item val not found in the set, then val is inserted into the set. 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 ensure 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; however, func must guarantee that during changing no any other modifications could be made on this item by concurrent threads.

You may pass func argument by reference using boost::ref or cds::ref.

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

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::erase ( Q const & val )

inline

Deletes the item from the set.

The function searches an item with key equal to val in the set, unlinks it from the set, and returns true. If the item with key equal to val 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Func >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::erase	(	const Q &	val,
		Func	f
	)

inline

Deletes the item from the set.

The function searches an item with key equal to val 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 ) ;
} ;

The functor may be passed by reference with boost:ref

If the item with key equal to val 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Less >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::erase_with	(	Q const &	val,
		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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Less , typename Func >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::erase_with	(	const Q &	val,
		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&, 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Func >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::find	(	Q &	val,
		Func	f
	)

inline

Finds the key val.

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

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

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

You can pass f argument by reference using boost::ref or cds::ref.

The functor may 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 val argument is non-const since it can be used as f functor destination i.e., the functor may 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 val is found, false otherwise.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Func >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::find	(	Q const &	val,
		Func	f
	)

inline

Finds the key val.

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

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

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

You can pass f argument by reference using boost::ref or cds::ref.

The functor may 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.

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 val is found, false otherwise.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::find ( Q const & val )

inline

Finds the key val.

The function searches the item with key equal to val and returns true if it 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Less , typename Func >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::find_with	(	Q &	val,
		Less	pred,
		Func	f
	)

inline

Finds the key val 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Less , typename Func >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::find_with	(	Q const &	val,
		Less	pred,
		Func	f
	)

inline

Finds the key val using pred predicate for searching.

The function is an analog of find(Q const&, 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Q , typename Less >

bool cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >::find_with	(	Q const &	val,
		Less	pred
	)

inline

Finds the key val using pred predicate for searching.

The function is an analog of find(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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

bool cds::intrusive::MichaelHashSet< GC, 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.

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

template<typename Func >

bool cds::intrusive::MichaelHashSet< GC, 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. User-defined functor f should guarantee that during changing val no any other changes could be made on this set's item by concurrent threads. The user-defined functor is called only if the inserting is success and can be passed by reference using boost::ref

template<class GC , class OrderedList , class Traits = michael_set::type_traits>

bool cds::intrusive::MichaelHashSet< GC, 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.

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

cds/intrusive/michael_set.h

Public Types

Public Member Functions

Protected Member Functions

Protected Attributes

Private Member Functions

Detailed Description

template<class GC, class OrderedList, class Traits = michael_set::type_traits> class cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >

Member Typedef Documentation

Constructor & Destructor Documentation

Member Function Documentation

template<class GC, class OrderedList, class Traits = michael_set::type_traits>
class cds::intrusive::MichaelHashSet< GC, OrderedList, Traits >