cds
2.3.2
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Michael's hash map. More...
#include <cds/container/michael_map.h>
Public Types | |
typedef GC | gc |
Garbage collector. | |
typedef OrderedList | ordered_list |
type of ordered list to be used as a bucket | |
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 map | |
typedef traits::allocator | allocator |
Bucket table allocator. | |
typedef ordered_list::key_comparator | key_comparator |
key compare functor | |
typedef ordered_list::stat | stat |
typedef ordered_list::guarded_ptr | guarded_ptr |
Guarded pointer - a result of get() and extract() functions. | |
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. | |
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 (K &&key) |
Inserts new node with key and default value. More... | |
template<typename K , typename V > | |
bool | insert (K &&key, V &&val) |
Inserts new node. More... | |
template<typename K , typename Func > | |
bool | insert_with (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 &&key, Func func, bool bAllowInsert=true) |
Updates data by key . More... | |
template<typename Q , typename V > | |
std::pair< bool, bool > | upsert (Q &&key, V &&val, bool bAllowInsert=true) |
Inserts or updates the node (only for IterableKVList ) 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 (K const &key) |
Deletes 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) |
Deletes 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... | |
bool | erase_at (iterator const &iter) |
Deletes the item pointed by iterator iter (only for IterableList based map) More... | |
template<typename K > | |
guarded_ptr | extract (K const &key) |
Extracts the item with specified key . More... | |
template<typename K , typename Less > | |
guarded_ptr | extract_with (K const &key, Less pred) |
Extracts the item using compare functor pred . More... | |
template<typename K , typename Func > | |
bool | find (K const &key, Func f) |
Finds the key key . More... | |
template<typename K > | |
iterator | find (K const &key) |
Finds key and returns iterator pointed to the item found (only for IterableList ) 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 , typename Less > | |
iterator | find_with (K const &key, Less pred) |
Finds key using pred predicate and returns iterator pointed to the item found (only for IterableList ) 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 > | |
guarded_ptr | get (K const &key) |
Finds key and return the item found. More... | |
template<typename K , typename Less > | |
guarded_ptr | get_with (K const &key, Less pred) |
Finds 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. 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 size_t | c_nHazardPtrCount = ordered_list::c_nHazardPtrCount |
Count of hazard pointer required. | |
Forward iterators (only for debugging purpose) | |
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. | |
Michael's hash map.
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. You may use any Garbage collector from the libcds
library. Note the GC
must be the same as the GC used for OrderedList
OrderedList
- ordered key-value list implementation used as bucket for hash map, for example, MichaelKVList
, LazyKVList
, IterableKVList
. 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
;key
of type K:
hash( key_type(key)) == hash( key )
key_type
and K
should be comparableThere are the specializations:
cds/container/michael_map_rcu.h
, see MichaelHashMap<RCU>.cds::gc::nogc
declared in cds/container/michael_map_nogc.h
, see MichaelHashMap<gc::nogc>.Suppose, you want to make int
to int
map for Hazard Pointer garbage collector. You should choose suitable ordered list class that will be used as a bucket for the map; it may be MichaelKVList
.
You may use option-based declaration:
typedef iterator_type< false > cds::container::MichaelHashMap< GC, OrderedList, Traits >::iterator |
Forward iterator.
The forward iterator for Michael's map has some features:
gc::HP
), a guard is a limited resource per thread, so an exception (or assertion) "no free guard" may be thrown if the limit of guard count per thread is exceeded.Iterator thread safety depends on type of OrderedList:
MichaelKVList
and LazyKVList:
iterator guarantees safety even if you delete the item that iterator points to because that item is guarded by hazard pointer. However, in case of concurrent deleting operations it is no guarantee that you iterate all item in the map. Moreover, a crash is possible when you try to iterate the next element that has been deleted by concurrent thread. Use this iterator on the concurrent container for debugging purpose only.IterableList:
iterator is thread-safe. You may use it freely in concurrent environment.The iterator interface:
typedef ordered_list::stat cds::container::MichaelHashMap< GC, OrderedList, Traits >::stat |
Internal statistics
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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.
nMaxItemCount | estimation of max item count in the hash map |
nLoadFactor | load factor: estimation of max number of items in the bucket |
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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.
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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.
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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.
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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.
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Checks if the map is empty.
atomicity::empty_item_counter
in traits::item_counter
, the function always returns true
.
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Deletes the item pointed by iterator iter
(only for IterableList
based map)
Returns true
if the operation is successful, false
otherwise. The function can return false
if the node the iterator points to has already been deleted by other thread.
The function does not invalidate the iterator, it remains valid and can be used for further traversing.
erase_at
() is supported only for MichaelHashMap
based on IterableList
.
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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.
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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.
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Extracts the item with specified key
.
The function searches an item with key equal to key
, unlinks it from the map, and returns it as guarded_ptr
. If key
is not found the function returns an empty guarded pointer.
Note the compare functor should accept a parameter of type K
that may be not the same as key_type
.
The extracted item is freed automatically when returned guarded_ptr
object will be destroyed or released.
guarded_ptr
object uses the GC's guard that can be limited resource.Usage:
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Extracts the item using compare functor pred
.
The function is an analog of extract(K const&) but pred
predicate is used for key comparing.
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.
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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:
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 returns true
if key
is found, false
otherwise.
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Finds key
and returns iterator pointed to the item found (only for IterableList
)
If key
is not found the function returns end()
.
IterableList
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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.
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Finds key
using pred
predicate and returns iterator pointed to the item found (only for IterableList
)
The function is an analog of find(K&)
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.
If key
is not found the function returns end()
.
IterableList
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Finds key
and return the item found.
The function searches the item with key equal to key
and returns the guarded pointer to the item found. If key
is not found the function returns an empty guarded pointer,
guarded_ptr
object uses one GC's guard which can be limited resource.Usage:
Note the compare functor specified for OrderedList
template parameter should accept a parameter of type K
that can be not the same as key_type
.
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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.
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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:
key_type
should be constructible from value of type K
. In trivial case, K
is equal to key_type
.mapped_type
should be default-constructible.Returns true
if inserting successful, false
otherwise.
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Inserts new node.
The function creates a node with copy of val
value and then inserts the node created into the map.
Preconditions:
key_type
should be constructible from key
of type K
.mapped_type
should be constructible from val
of type V
.Returns true
if val
is inserted into the map, false
otherwise.
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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
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:
key
;func
functorThis 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.
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Returns item count in the map.
If you use atomicity::empty_item_counter
in traits::item_counter
, the function always returns 0.
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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 depends on OrderedList:
for MichaelKVList
, LazyKVList
with arguments:
bNew
- true
if the item has been inserted, false
otherwiseitem
- the item found or insertedThe functor may change any fields of the item.second
that is mapped_type
.
for IterableKVList
where
val
- a new data constructed from key
old
- old value that will be retired. If new item has been inserted then old
is nullptr
.The functor may change non-key fields of val
; however, func
must guarantee that during changing no any other modifications could be made on this item by concurrent threads.
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.
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Inserts or updates the node (only for IterableKVList
)
The operation performs inserting or changing data with lock-free manner.
If key
is not found in the map, then key
is inserted iff bAllowInsert
is true
. Otherwise, the current element is changed to val
, the old element will be retired later.
Returns std::pair<bool, bool> where first
is true
if operation is successful, second
is true
if val
has been added or false
if the item with that key already in the map.