cds
2.3.2
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Cuckoo hash set. More...
#include <cds/intrusive/cuckoo_set.h>
Public Types | |
typedef T | value_type |
The value type stored in the set. | |
typedef Traits | traits |
Set traits. | |
typedef traits::hook | hook |
hook type | |
typedef hook::node_type | node_type |
node type | |
typedef get_node_traits< value_type, node_type, hook >::type | node_traits |
node traits | |
typedef traits::hash | hash |
hash functor tuple wrapped for internal use | |
typedef hash::hash_tuple_type | hash_tuple_type |
Type of hash tuple. | |
typedef traits::stat | stat |
internal statistics type | |
typedef traits::mutex_policy | original_mutex_policy |
Concurrent access policy, see cuckoo::traits::mutex_policy . | |
typedef opt::details::make_equal_to< value_type, traits, !c_isSorted >::type | key_equal_to |
Key equality functor; used only for unordered probe-set. | |
typedef opt::details::make_comparator< value_type, traits >::type | key_comparator |
key comparing functor based on opt::compare and opt::less option setter. Used only for ordered probe set | |
typedef traits::allocator | allocator |
allocator type | |
typedef traits::item_counter | item_counter |
item counter type | |
typedef traits::disposer | disposer |
node disposer | |
Public Member Functions | |
CuckooSet () | |
Default constructor. More... | |
CuckooSet (size_t nInitialSize, unsigned int nProbesetSize, unsigned int nProbesetThreshold=0) | |
Constructs the set object with given probe set size and threshold. More... | |
CuckooSet (hash_tuple_type const &h) | |
Constructs the set object with given hash functor tuple. More... | |
CuckooSet (size_t nInitialSize, unsigned int nProbesetSize, unsigned int nProbesetThreshold, hash_tuple_type const &h) | |
Constructs the set object with given probe set properties and hash functor tuple. More... | |
CuckooSet (hash_tuple_type &&h) | |
Constructs the set object with given hash functor tuple (move semantics) More... | |
CuckooSet (size_t nInitialSize, unsigned int nProbesetSize, unsigned int nProbesetThreshold, hash_tuple_type &&h) | |
Constructs the set object with given probe set properties and hash functor tuple (move semantics) More... | |
~CuckooSet () | |
Destructor. | |
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 node. More... | |
bool | unlink (value_type &val) |
Unlink the item val from the set. More... | |
template<typename Q > | |
value_type * | erase (Q const &val) |
Deletes the item from the set. More... | |
template<typename Q , typename Predicate > | |
value_type * | erase_with (Q const &val, Predicate pred) |
Deletes the item from the set using pred predicate for searching. More... | |
template<typename Q , typename Func > | |
value_type * | erase (Q const &val, Func f) |
Delete the item from the set. More... | |
template<typename Q , typename Predicate , typename Func > | |
value_type * | erase_with (Q const &val, Predicate 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) |
Find the key val . More... | |
template<typename Q , typename Predicate , typename Func > | |
bool | find_with (Q &val, Predicate pred, Func f) |
Find the key val using pred predicate for comparing. More... | |
template<typename Q > | |
bool | contains (Q const &key) |
Checks whether the set contains key . More... | |
template<typename Q , typename Predicate > | |
bool | contains (Q const &key, Predicate pred) |
Checks whether the set contains key using pred predicate for searching. More... | |
void | clear () |
Clears the set. More... | |
template<typename Disposer > | |
void | clear_and_dispose (Disposer oDisposer) |
Clears the set and calls disposer for each item. 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... | |
size_t | lock_count () const |
Returns lock array size. | |
stat const & | statistics () const |
Returns const reference to internal statistics. | |
mutex_policy::statistics_type const & | mutex_policy_statistics () const |
Returns const reference to mutex policy internal statistics. | |
Static Public Attributes | |
static bool const | c_isSorted |
Probe set should be ordered or not. More... | |
static size_t const | c_nArity = hash::size |
the arity of cuckoo hashing: the number of hash functors provided; minimum 2. | |
static unsigned int const | c_nDefaultProbesetSize = 4 |
default probeset size | |
static size_t const | c_nDefaultInitialSize = 16 |
default initial size | |
static unsigned int const | c_nRelocateLimit = c_nArity * 2 - 1 |
Count of attempts to relocate before giving up. | |
Protected Attributes | |
bucket_entry * | m_BucketTable [c_nArity] |
Bucket tables. | |
atomics::atomic< size_t > | m_nBucketMask |
Hash bitmask; bucket table size minus 1. | |
unsigned int const | m_nProbesetSize |
Probe set size. | |
unsigned int const | m_nProbesetThreshold |
Probe set threshold. | |
hash | m_Hash |
Hash functor tuple. | |
mutex_policy | m_MutexPolicy |
concurrent access policy | |
item_counter | m_ItemCounter |
item counter | |
stat | m_Stat |
internal statistics | |
Cuckoo hash set.
Source
About Cuckoo hashing
[From "The Art of Multiprocessor Programming"] Cuckoo hashing is a hashing algorithm in which a newly added item displaces any earlier item occupying the same slot. For brevity, a table is a k-entry array of items. For a hash set of size N = 2k we use a two-entry array of tables, and two independent hash functions, h0, h1: KeyRange -> 0,...,k-1
mapping the set of possible keys to entries in he array. To test whether a value x
is in the set, find(x)
tests whether either table[0][h0(x)]
or table[1][h1(x)]
is equal to x
. Similarly, erase(x)
checks whether x
is in either table[0][h0(x)]
or table[1][h1(x)]
, ad removes it if found.
The insert(x)
successively "kicks out" conflicting items until every key has a slot. To add x
, the method swaps x
with y
, the current occupant of table[0][h0(x)]
. If the prior value was nullptr
, it is done. Otherwise, it swaps the newly nest-less value y
for the current occupant of table[1][h1(y)]
in the same way. As before, if the prior value was nullptr
, it is done. Otherwise, the method continues swapping entries (alternating tables) until it finds an empty slot. We might not find an empty slot, either because the table is full, or because the sequence of displacement forms a cycle. We therefore need an upper limit on the number of successive displacements we are willing to undertake. When this limit is exceeded, we resize the hash table, choose new hash functions and start over.
For concurrent cuckoo hashing, rather than organizing the set as a two-dimensional table of items, we use two-dimensional table of probe sets, where a probe set is a constant-sized set of items with the same hash code. Each probe set holds at most PROBE_SIZE
items, but the algorithm tries to ensure that when the set is quiescent (i.e no method call in progress) each probe set holds no more than THRESHOLD < PROBE_SET
items. While method calls are in-flight, a probe set may temporarily hold more than THRESHOLD
but never more than PROBE_SET
items.
In current implementation, a probe set can be defined either as a (single-linked) list or as a fixed-sized vector, optionally ordered.
In description above two-table cuckoo hashing (k = 2
) has been considered. We can generalize this approach for k >= 2
when we have k
hash functions h[0], ... h[k-1]
and k
tables table[0], ... table[k-1]
.
The search in probe set is linear, the complexity is O(PROBE_SET)
. The probe set may be ordered or not. Ordered probe set can be more efficient since the average search complexity is O(PROBE_SET/2)
. However, the overhead of sorting can eliminate a gain of ordered search.
The probe set is ordered if compare
or less
is specified in Traits
template parameter. Otherwise, the probe set is unordered and Traits
should provide equal_to
predicate.
The cds::intrusive::cuckoo
namespace contains CuckooSet-related
declarations.
Template arguments:
T
- the type stored in the set. The type must be based on cuckoo::node
(for cuckoo::base_hook
) or it must have a member of type cuckoo::node (for cuckoo::member_hook
), or it must be convertible to cuckoo::node
(for cuckoo::traits_hook
)Traits
- type traits, default is cuckoo::traits
. It is possible to declare option-based set with cuckoo::make_traits
metafunction result as Traits
template argument.How to use
You should incorporate cuckoo::node
into your struct T
and provide appropriate cuckoo::traits::hook
in your Traits
template parameters. Usually, for Traits
you define a struct based on cuckoo::traits
.
Example for base hook and list-based probe-set:
If we provide compare
function instead of equal_to
for my_data
we get as a result a cuckoo set with ordered probe set that may improve performance. Example for base hook and ordered vector-based probe-set:
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inline |
Default constructor.
Initial size = c_nDefaultInitialSize
Probe set size:
c_nDefaultProbesetSize
if probeset_type
is cuckoo::list
Capacity
if probeset_type
is cuckoo::vector<Capacity>
Probe set threshold = probe set size - 1
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inline |
Constructs the set object with given probe set size and threshold.
If probe set type is cuckoo::vector<Capacity>
vector then nProbesetSize
is ignored since it should be equal to vector's Capacity
.
nInitialSize | Initial set size; if 0 - use default initial size c_nDefaultInitialSize |
nProbesetSize | probe set size |
nProbesetThreshold | probe set threshold, nProbesetThreshold < nProbesetSize . If 0, nProbesetThreshold = nProbesetSize - 1 |
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inline |
Constructs the set object with given hash functor tuple.
The probe set size and threshold are set as default, see CuckooSet()
h | hash functor tuple of type std::tuple<H1, H2, ... Hn> where n == c_nArity |
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inline |
Constructs the set object with given probe set properties and hash functor tuple.
If probe set type is cuckoo::vector<Capacity>
vector then nProbesetSize
should be equal to vector's Capacity
.
nInitialSize | Initial set size; if 0 - use default initial size c_nDefaultInitialSize |
nProbesetSize | probe set size, positive integer |
nProbesetThreshold | probe set threshold, nProbesetThreshold < nProbesetSize . If 0, nProbesetThreshold = nProbesetSize - 1 |
h | hash functor tuple of type std::tuple<H1, H2, ... Hn> where n == c_nArity |
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inline |
Constructs the set object with given hash functor tuple (move semantics)
The probe set size and threshold are set as default, see CuckooSet()
h | hash functor tuple of type std::tuple<H1, H2, ... Hn> where n == c_nArity |
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inline |
Constructs the set object with given probe set properties and hash functor tuple (move semantics)
If probe set type is cuckoo::vector<Capacity>
vector then nProbesetSize
should be equal to vector's Capacity
.
nInitialSize | Initial set size; if 0 - use default initial size c_nDefaultInitialSize |
nProbesetSize | probe set size, positive integer |
nProbesetThreshold | probe set threshold, nProbesetThreshold < nProbesetSize . If 0, nProbesetThreshold = nProbesetSize - 1 |
h | hash functor tuple of type std::tuple<H1, H2, ... Hn> where n == c_nArity |
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inline |
Returns the size of hash table.
The hash table size is non-constant and can be increased via resizing.
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inline |
Clears the set.
The function unlinks all items from the set. For any item Traits::disposer
is called
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inline |
Clears the set and calls disposer
for each item.
The function unlinks all items from the set calling oDisposer
for each item. Disposer
functor interface is:
The Traits::disposer
is not called.
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inline |
Checks whether the set 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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inline |
Checks whether the set contains key
using pred
predicate for searching.
The function is similar to contains( key )
but pred
is used for key comparing. If the set is unordered, Predicate
has semantics like std::equal_to
. For ordered set Predicate
has std::less
semantics. In that case pred
must imply the same element order as the comparator used for building the set.
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inline |
Checks if the set is empty.
Emptiness is checked by item counting: if item count is zero then the set is empty.
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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 a pointer to unlinked item.
If the item with key equal to val
is not found the function return nullptr
.
Note the hash functor should accept a parameter of type Q
that can be not the same as value_type
.
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inline |
Delete the item from the set.
The function searches an item with key equal to val
in the set, call f
functor with item found, unlinks it from the set, and returns a pointer to unlinked item.
The Func
interface is
If the item with key equal to val
is not found the function return nullptr
.
Note the hash functor should accept a parameter of type Q
that can be not the same as value_type
.
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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. If cuckoo set is ordered, then Predicate
should have the interface and semantics like std::less
. If cuckoo set is unordered, then Predicate
should have the interface and semantics like std::equal_to
. Predicate
must imply the same element order as the comparator used for building the set.
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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. If you use ordered cuckoo set, then Predicate
should have the interface and semantics like std::less
. If you use unordered cuckoo set, then Predicate
should have the interface and semantics like std::equal_to
. Predicate
must imply the same element order as the comparator used for building the set.
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inline |
Find 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:
where item
is the item found, val
is the find
function argument.
The functor may change non-key fields of item
.
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.
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inline |
Find the key val
using pred
predicate for comparing.
The function is an analog of find(Q&, Func) but pred
is used for key comparison. If you use ordered cuckoo set, then Predicate
should have the interface and semantics like std::less
. If you use unordered cuckoo set, then Predicate
should have the interface and semantics like std::equal_to
. pred
must imply the same element order as the comparator used for building the set.
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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 inserted into the set, false
otherwise.
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inline |
Inserts new node.
The function allows to split creating of new item into two part:
f
functor to initialize value-field of val
.The functor signature is:
where val
is the item inserted.
The user-defined functor is called only if the inserting is success.
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inline |
Unlink the item val
from the set.
The function searches the item val
in the set and unlink it if it is found and is equal to val
(here, the equality means that val
belongs to the set: if item
is an item found then unlink is successful iif &val == &item
)
The function returns true
if success and false
otherwise.
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inline |
Updates the node.
The operation performs inserting or changing data with lock-free manner.
If the item val
is not found in the set, then val
is inserted into the set iff bAllowInsert
is true
. Otherwise, the functor func
is called with item found. The functor func
signature is:
with arguments:
bNew
- true
if the item has been inserted, false
otherwiseitem
- item of the setval
- argument val
passed into the update
() function If new item has been inserted (i.e. bNew
is true
) then item
and val
arguments refer 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, i.e. the node has been inserted or updated, second
is true
if new item has been added or false
if the item with key
already exists.
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static |
Probe set should be ordered or not.
If Traits
specifies cmpare
or less
functor then the set is ordered. Otherwise, it is unordered and Traits
should provide equal_to
functor.