cds
2.3.2
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Michael's hash set. More...
#include <cds/container/michael_set.h>
Public Types | |
typedef GC | gc |
Garbage collector. | |
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 to be stored in the list | |
typedef ordered_list::key_comparator | key_comparator |
key comparison 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 internal_bucket_type::guarded_ptr | guarded_ptr |
Guarded pointer - a result of get() and extract() functions. | |
Public Member Functions | |
MichaelHashSet (size_t nMaxItemCount, size_t nLoadFactor) | |
Initialize hash set. More... | |
~MichaelHashSet () | |
Clears hash set and destroys it. | |
template<typename Q > | |
bool | insert (Q &&val) |
Inserts new node. More... | |
template<typename Q , typename Func > | |
bool | insert (Q &&val, Func f) |
Inserts new node. More... | |
template<typename Q , typename Func > | |
std::pair< bool, bool > | update (Q &&val, Func func, bool bAllowUpdate=true) |
Updates the element. More... | |
template<typename Q > | |
std::pair< bool, bool > | upsert (Q &&val, bool bAllowInsert=true) |
Inserts or updates the node (only for IterableList ) More... | |
template<typename... Args> | |
bool | emplace (Args &&... args) |
Inserts data of type value_type constructed from args . More... | |
template<typename Q > | |
bool | erase (Q const &key) |
Deletes key 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 (Q const &key, Func f) |
Deletes key from the set. More... | |
template<typename Q , typename Less , typename Func > | |
bool | erase_with (Q const &key, Less pred, Func f) |
Deletes the item from the set using pred predicate for searching. More... | |
bool | erase_at (iterator const &iter) |
Deletes the item pointed by iterator iter (only for IterableList based set) More... | |
template<typename Q > | |
guarded_ptr | extract (Q const &key) |
Extracts the item with specified key . More... | |
template<typename Q , typename Less > | |
guarded_ptr | extract_with (Q const &key, Less pred) |
Extracts the item using compare functor pred . More... | |
template<typename Q , typename Func > | |
bool | find (Q &key, Func f) |
Finds the key key . More... | |
template<typename Q > | |
iterator | find (Q &key) |
Finds key and returns iterator pointed to the item found (only for IterableList ) 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 , typename Less > | |
iterator | find_with (Q &key, Less pred) |
Finds key using pred predicate and returns iterator pointed to the item found (only for IterableList ) 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 > | |
guarded_ptr | get (Q const &key) |
Finds the key key and return the item found. More... | |
template<typename Q , typename Less > | |
guarded_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... | |
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 size_t | c_nHazardPtrCount = ordered_list::c_nHazardPtrCount |
Count of hazard pointer required. | |
Forward iterators | |
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. | |
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. | |
Michael's hash set.
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 list implementation used as bucket for hash set, possible implementations: MichaelList
, LazyList
, IterableList
. The ordered list implementation specifies the type T
to be stored in the hash-set, the comparing functor for the type T
and other features specific for the ordered list.Traits
- set traits, default is michael_set::traits
. Instead of defining Traits
struct you may use option-based syntax with michael_set::make_traits
metafunction.There are the specializations:
cd/container/michael_set_rcu.h
, see MichaelHashSet<RCU>.cds/container/michael_set_nogc.h
, see MichaelHashSet<gc::nogc>.Some member functions of Michael's hash set accept the key parameter of type Q
which differs from node type value_type
. It is expected that type Q
contains full key of node type value_type
, and if keys of type Q
and value_type
are equal the hash values of these keys must be equal too.
The hash functor Traits::hash
should accept parameters of both type:
How to use
Suppose, we have the following type Foo
that we want to store in our MichaelHashSet
:
To use MichaelHashSet
for Foo
values, you should first choose suitable ordered list class that will be used as a bucket for the set. We will use gc::DHP
reclamation schema and MichaelList
as a bucket type. Also, for ordered list we should develop a comparator for our Foo
struct.
typedef michael_set::details::iterator< internal_bucket_type, false > cds::container::MichaelHashSet< GC, OrderedList, Traits >::iterator |
Forward iterator.
The forward iterator for Michael's set 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:
MichaelList
and LazyList:
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 set. 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:
Forward iterator
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inline |
Initialize 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)
].
The ctor defines hash table size as rounding nMaxItemCount / nLoadFactor
up to nearest power of two.
nMaxItemCount | estimation of max item count in the hash set |
nLoadFactor | load factor: estimation of max number of items in the bucket |
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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.
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Clears the set (non-atomic)
The function erases 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.
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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
.
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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.
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Inserts data of type value_type
constructed from args
.
Returns true
if inserting successful, false
otherwise.
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Checks if the set is empty.
atomicity::empty_item_counter
in traits::item_counter
, the function always returns true
.
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Deletes key
from the set.
Since the key of MichaelHashSet's item type value_type
is not explicitly specified, template parameter Q
defines the key type searching in the list. The set item comparator should be able to compare the type value_type
and the type Q
.
Return true
if key is found and deleted, false
otherwise.
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Deletes key
from the set.
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:
where item
- the item found.
Since the key of MichaelHashSet's value_type
is not explicitly specified, template parameter Q
defines the key type searching in the list. The list item comparator should be able to compare the type T
of list item and the type Q
.
Return true
if key is found and deleted, false
otherwise
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Deletes the item pointed by iterator iter
(only for IterableList
based set)
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 MichaelHashSet
based on IterableList
.
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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
. Less
must imply the same element order as the comparator used for building the set.
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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
. Less
must imply the same element order as the comparator used for building the set.
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Extracts the item with specified key
.
The function searches an item with key equal to key
, unlinks it from the set, and returns it as guarded_ptr
. If key
is not found the function returns an empty guadd pointer.
Note the compare functor should accept a parameter of type Q
that may be not the same as value_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(Q const&)
but pred
predicate is used for key comparing.
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.
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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, key
is the find
function argument.
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's 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 may be not the same as value_type
.
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 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
. Less
must imply the same element order as the comparator used for building the set.
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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(Q&)
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 the key 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 functin 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 Q
that can be not the same as value_type
.
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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.
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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 set.
The type Q
should contain as minimum the complete key for the node. The object of value_type should be constructible from a value of type Q
. In trivial case, Q
is equal to value_type.
Returns true
if val
is inserted into the set, false
otherwise.
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Inserts new node.
The function allows to split creating of new item into two part:
f
functor to initialize value-fields 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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Returns item count in the set.
atomicity::empty_item_counter
in traits::item_counter
, the function always returns 0.
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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 func
signature depends of OrderedList:
for MichaelList
, LazyList
with arguments:
bNew
- true
if the item has been inserted, false
otherwiseitem
- item of the setval
- argument val
passed into the update
() functionThe functor may change non-key fields of the item
.
for IterableList
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
. 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.
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Inserts or updates the node (only for IterableList
)
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 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 set.