cds  2.2.0
cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits > Class Template Reference

Michael's hash map (template specialization for RCU) More...

#include <cds/container/michael_map_rcu.h>

Public Types

typedef cds::urcu::gc< RCU > gc
 RCU used as garbage collector.
 
typedef OrderedList ordered_list
 type of ordered list used as a bucket implementation
 
typedef Traits traits
 Map traits.
 
typedef ordered_list::key_type key_type
 key type
 
typedef ordered_list::mapped_type mapped_type
 value type
 
typedef ordered_list::value_type value_type
 key/value pair stored in the list
 
typedef ordered_list::key_comparator key_comparator
 key comparison functor
 
typedef ordered_list::stat stat
 Internal statistics.
 
typedef ordered_list::exempt_ptr exempt_ptr
 
typedef ordered_list::raw_ptr raw_ptr
 Type of get() member function return value.
 
typedef ordered_list::rcu_lock rcu_lock
 RCU scoped lock.
 
typedef cds::opt::v::hash_selector< typename traits::hash >::type hash
 Hash functor for key_type and all its derivatives that you use.
 
typedef traits::item_counter item_counter
 Item counter type.
 
typedef traits::allocator allocator
 Bucket table allocator.
 

Public Member Functions

 MichaelHashMap (size_t nMaxItemCount, size_t nLoadFactor)
 Initializes the map. More...
 
 ~MichaelHashMap ()
 Clears hash map and destroys it.
 
template<typename K >
bool insert (const K &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 Func >
std::pair< bool, bool > update (K const &key, Func func, bool bAllowInsert=true)
 Updates data by key. More...
 
template<typename K , typename... Args>
bool emplace (K &&key, Args &&... args)
 For key key inserts data of type mapped_type created from args. More...
 
template<typename K >
bool erase (const K &key)
 Deletes key from the map. More...
 
template<typename K , typename Less >
bool erase_with (const K &key, Less pred)
 Deletes the item from the map using pred predicate for searching. More...
 
template<typename K , typename Func >
bool erase (const K &key, Func f)
 Deletes key from the map. More...
 
template<typename K , typename Less , typename Func >
bool erase_with (const K &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 an item from the map. More...
 
template<typename K , typename Less >
exempt_ptr extract_with (K const &key, Less pred)
 Extracts an item from the map using pred predicate for searching. More...
 
template<typename K , typename Func >
bool find (K const &key, Func f)
 Finds 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 key and return the item found. More...
 
template<typename K , typename Less >
raw_ptr get_with (K const &key, Less pred)
 Finds key and return the item found. More...
 
void clear ()
 Clears the map (not atomic) More...
 
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.
 
size_t bucket_count () const
 Returns the size of hash table. More...
 

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 iterator_type< false > iterator
 Forward iterator. More...
 
typedef iterator_type< true > const_iterator
 Const forward iterator.
 
iterator begin ()
 Returns a forward iterator addressing the first element in a map. More...
 
iterator end ()
 Returns an iterator that addresses the location succeeding the last element in a map. More...
 
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.
 
const_iterator end () const
 Returns an const iterator that addresses the location succeeding the last element in a map.
 
const_iterator cend () const
 Returns an const iterator that addresses the location succeeding the last element in a map.
 

Detailed Description

template<class RCU, class OrderedList, class Traits = michael_map::traits>
class cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >

Michael's hash map (template specialization for RCU)

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 key-value list implementation used as bucket for hash map, for example, MichaelKVList. The ordered list implementation specifies the Key and Value types stored in the hash-map, the reclamation schema GC used by hash-map, the comparison functor for the type Key and other features specific for the ordered list.
  • Traits - map traits, default is michael_map::traits. Instead of defining Traits struct you may use option-based syntax with michael_map::make_traits metafunction

Many of the class function take a key argument of type K that in general is not key_type. key_type and an argument of template type K must meet the following requirements:

  • key_type should be constructible from value of type K;
  • the hash functor should be able to calculate correct hash value from argument key of type K: hash( key_type(key)) == hash( key )
  • values of type key_type and K should be comparable

How to use

The tips about how to use Michael's map see MichaelHashMap. Remember, that you should include RCU-related header file (for example, cds/urcu/general_buffered.h) before including cds/container/michael_map_rcu.h.

Member Typedef Documentation

§ exempt_ptr

template<class RCU , class OrderedList , class Traits = michael_map::traits>
typedef ordered_list::exempt_ptr cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::exempt_ptr

pointer to extracted node

§ iterator

template<class RCU , class OrderedList , class Traits = michael_map::traits>
typedef iterator_type< false > cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::iterator

Forward iterator.

The forward iterator for Michael's map 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
// 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;
};

Constructor & Destructor Documentation

§ MichaelHashMap()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::MichaelHashMap ( size_t  nMaxItemCount,
size_t  nLoadFactor 
)
inline

Initializes the map.

The Michael's hash map 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
nMaxItemCountestimation of max item count in the hash map
nLoadFactorload factor: estimation of max number of items in the bucket

Member Function Documentation

§ begin()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
iterator cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::begin ( )
inline

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

For empty map

begin() == end()

§ bucket_count()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
size_t cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::bucket_count ( ) const
inline

Returns the size of hash table.

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

§ clear()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
void cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::clear ( )
inline

Clears the map (not atomic)

The function erases all items from the map.

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 map may contain item(s). Therefore, clear may be used only for debugging purposes.

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

§ contains() [1/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, 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.

§ contains() [2/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Less >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::contains ( K const &  key,
Less  pred 
)
inline

Checks whether the map 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 map.

§ emplace()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename... Args>
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::emplace ( K &&  key,
Args &&...  args 
)
inline

For key key inserts data of type mapped_type created from args.

key_type should be constructible from type K

Returns true if inserting successful, false otherwise.

§ empty()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, 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. Thus, the correct item counting is an important part of the map implementation.

§ end()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
iterator cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::end ( )
inline

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

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 map. For empty map

begin() == end()

§ erase() [1/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::erase ( const K &  key)
inline

Deletes 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

§ erase() [2/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Func >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::erase ( const K &  key,
Func  f 
)
inline

Deletes 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

§ erase_with() [1/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Less >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::erase_with ( const K &  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 predicate has the interface like std::less. Less must imply the same element order as the comparator used for building the map.

§ erase_with() [2/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Less , typename Func >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::erase_with ( const K &  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.

§ extract()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K >
exempt_ptr cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::extract ( K const &  key)
inline

Extracts an item from the map.

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

The function just excludes the key from the map and returns a pointer to item found. 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/container/michael_kvlist_rcu.h>
#include <cds/container/michael_map_rcu.h>
typedef cds::urcu::gc< general_buffered<> > rcu;
rcu_michael_map theMap;
// ...
rcu_michael_map::exempt_ptr p;
// For MichaelList we should not lock RCU
// Note that you must not delete the item found inside the RCU lock
p = theMap.extract( 10 );
if ( p ) {
// do something with p
...
}
// We may safely release p here
// release() passes the pointer to RCU reclamation cycle
p.release();

§ extract_with()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Less >
exempt_ptr cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::extract_with ( K const &  key,
Less  pred 
)
inline

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

The function is an analog of extract(K 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 map.

§ find()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Func >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::find ( K const &  key,
Func  f 
)
inline

Finds 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. 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 map's item. If such access is possible you must provide your own synchronization schema on item level to exclude unsafe item modifications.

The function applies RCU lock internally.

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

§ find_with()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Less , typename Func >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, 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.

§ get()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K >
raw_ptr cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::get ( K const &  key)
inline

Finds 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 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:

hash_map theMap;
// ...
typename hash_map::raw_ptr gp;
{
// Lock RCU
hash_map::rcu_lock lock;
gp = theMap.get( 5 );
if ( gp ) {
// Deal with gp
//...
}
// Unlock RCU by rcu_lock destructor
// gp can be reclaimed at any time after RCU has been unlocked
}

§ get_with()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Less >
raw_ptr cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::get_with ( K const &  key,
Less  pred 
)
inline

Finds 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.

§ insert() [1/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::insert ( const K &  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 value of type K. In trivial case, K is equal to key_type.
  • The mapped_type should be default-constructible.

The function applies RCU lock internally.

Returns true if inserting successful, false otherwise.

§ insert() [2/2]

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename V >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, 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 mapped_type should be constructible from val of type V.

The function applies RCU lock internally.

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

§ insert_with()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Func >
bool cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, 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 user-defined functor is called only if inserting is successful.

The key_type should be constructible from value of type K.

The function allows to split creating of new item into two 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 mapped_type is heavyweight and it is preferable that the initialization should be completed only if inserting is successful.

The function applies RCU lock internally.

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

§ update()

template<class RCU , class OrderedList , class Traits = michael_map::traits>
template<typename K , typename Func >
std::pair<bool, bool> cds::container::MichaelHashMap< cds::urcu::gc< RCU >, OrderedList, Traits >::update ( K const &  key,
Func  func,
bool  bAllowInsert = true 
)
inline

Updates data by key.

The operation performs inserting or replacing the element with lock-free manner.

If the key not found in the map, then the new item created from key will be inserted into the map iff bAllowInsert is true. (note that in this case the key_type should be constructible from type K). Otherwise, if key is found, the functor func is called with item found.

The functor Func signature is:

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

with arguments:

  • bNew - true if the item has been inserted, false otherwise
  • item - the item found or inserted

The functor may change any fields of the item.second that is mapped_type.

The function applies RCU lock internally.

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
For MichaelKVList as the bucket see insert item troubleshooting. LazyKVList 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 2.2.0 Developed by Maxim Khizhinsky aka khizmax 2007 - 2017
Autogenerated Wed Jan 4 2017 08:49:38 by Doxygen 1.8.12