[#concurrent_node_map] == Class Template concurrent_node_map :idprefix: concurrent_node_map_ `boost::concurrent_node_map` — A node-based hash table that associates unique keys with another value and allows for concurrent element insertion, erasure, lookup and access without external synchronization mechanisms. Even though it acts as a container, `boost::concurrent_node_map` does not model the standard C++ https://en.cppreference.com/w/cpp/named_req/Container[Container^] concept. In particular, iterators and associated operations (`begin`, `end`, etc.) are not provided. Element access and modification are done through user-provided _visitation functions_ that are passed to `concurrent_node_map` operations where they are executed internally in a controlled fashion. Such visitation-based API allows for low-contention concurrent usage scenarios. The internal data structure of `boost::concurrent_node_map` is similar to that of `boost::unordered_node_map`. Unlike `boost::concurrent_flat_map`, pointer stability and node handling functionalities are provided, at the expense of potentially lower performance. === Synopsis [listing,subs="+macros,+quotes"] ----- // #include xref:reference/header_concurrent_node_map.adoc[``] namespace boost { namespace unordered { template, class Pred = std::equal_to, class Allocator = std::allocator>> class concurrent_node_map { public: // types using key_type = Key; using mapped_type = T; using value_type = std::pair; using init_type = std::pair< typename std::remove_const::type, typename std::remove_const::type >; using hasher = Hash; using key_equal = Pred; using allocator_type = Allocator; using pointer = typename std::allocator_traits::pointer; using const_pointer = typename std::allocator_traits::const_pointer; using reference = value_type&; using const_reference = const value_type&; using size_type = std::size_t; using difference_type = std::ptrdiff_t; using node_type = _implementation-defined_; using insert_return_type = _implementation-defined_; using stats = xref:reference/stats.adoc#stats_stats_type[__stats-type__]; // if statistics are xref:concurrent_node_map_boost_unordered_enable_stats[enabled] // constants static constexpr size_type xref:#concurrent_node_map_constants[bulk_visit_size] = _implementation-defined_; // construct/copy/destroy xref:#concurrent_node_map_default_constructor[concurrent_node_map](); explicit xref:#concurrent_node_map_bucket_count_constructor[concurrent_node_map](size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); template xref:#concurrent_node_map_iterator_range_constructor[concurrent_node_map](InputIterator f, InputIterator l, size_type n = _implementation-defined_, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); xref:#concurrent_node_map_copy_constructor[concurrent_node_map](const concurrent_node_map& other); xref:#concurrent_node_map_move_constructor[concurrent_node_map](concurrent_node_map&& other); template xref:#concurrent_node_map_iterator_range_constructor_with_allocator[concurrent_node_map](InputIterator f, InputIterator l,const allocator_type& a); explicit xref:#concurrent_node_map_allocator_constructor[concurrent_node_map](const Allocator& a); xref:#concurrent_node_map_copy_constructor_with_allocator[concurrent_node_map](const concurrent_node_map& other, const Allocator& a); xref:#concurrent_node_map_move_constructor_with_allocator[concurrent_node_map](concurrent_node_map&& other, const Allocator& a); xref:#concurrent_node_map_move_constructor_from_unordered_node_map[concurrent_node_map](unordered_node_map&& other); xref:#concurrent_node_map_initializer_list_constructor[concurrent_node_map](std::initializer_list il, size_type n = _implementation-defined_ const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); xref:#concurrent_node_map_bucket_count_constructor_with_allocator[concurrent_node_map](size_type n, const allocator_type& a); xref:#concurrent_node_map_bucket_count_constructor_with_hasher_and_allocator[concurrent_node_map](size_type n, const hasher& hf, const allocator_type& a); template xref:#concurrent_node_map_iterator_range_constructor_with_bucket_count_and_allocator[concurrent_node_map](InputIterator f, InputIterator l, size_type n, const allocator_type& a); template xref:#concurrent_node_map_iterator_range_constructor_with_bucket_count_and_hasher[concurrent_node_map](InputIterator f, InputIterator l, size_type n, const hasher& hf, const allocator_type& a); xref:#concurrent_node_map_initializer_list_constructor_with_allocator[concurrent_node_map](std::initializer_list il, const allocator_type& a); xref:#concurrent_node_map_initializer_list_constructor_with_bucket_count_and_allocator[concurrent_node_map](std::initializer_list il, size_type n, const allocator_type& a); xref:#concurrent_node_map_initializer_list_constructor_with_bucket_count_and_hasher_and_allocator[concurrent_node_map](std::initializer_list il, size_type n, const hasher& hf, const allocator_type& a); xref:#concurrent_node_map_destructor[~concurrent_node_map](); concurrent_node_map& xref:#concurrent_node_map_copy_assignment[operator++=++](const concurrent_node_map& other); concurrent_node_map& xref:#concurrent_node_map_move_assignment[operator++=++](concurrent_node_map&& other) ++noexcept( (boost::allocator_traits::is_always_equal::value || boost::allocator_traits::propagate_on_container_move_assignment::value) && std::is_same::value);++ concurrent_node_map& xref:#concurrent_node_map_initializer_list_assignment[operator++=++](std::initializer_list); allocator_type xref:#concurrent_node_map_get_allocator[get_allocator]() const noexcept; // visitation template size_t xref:#concurrent_node_map_cvisit[visit](const key_type& k, F f); template size_t xref:#concurrent_node_map_cvisit[visit](const key_type& k, F f) const; template size_t xref:#concurrent_node_map_cvisit[cvisit](const key_type& k, F f) const; template size_t xref:#concurrent_node_map_cvisit[visit](const K& k, F f); template size_t xref:#concurrent_node_map_cvisit[visit](const K& k, F f) const; template size_t xref:#concurrent_node_map_cvisit[cvisit](const K& k, F f) const; template size_t xref:concurrent_node_map_bulk_visit[visit](FwdIterator first, FwdIterator last, F f); template size_t xref:concurrent_node_map_bulk_visit[visit](FwdIterator first, FwdIterator last, F f) const; template size_t xref:concurrent_node_map_bulk_visit[cvisit](FwdIterator first, FwdIterator last, F f) const; template size_t xref:#concurrent_node_map_cvisit_all[visit_all](F f); template size_t xref:#concurrent_node_map_cvisit_all[visit_all](F f) const; template size_t xref:#concurrent_node_map_cvisit_all[cvisit_all](F f) const; template void xref:#concurrent_node_map_parallel_cvisit_all[visit_all](ExecutionPolicy&& policy, F f); template void xref:#concurrent_node_map_parallel_cvisit_all[visit_all](ExecutionPolicy&& policy, F f) const; template void xref:#concurrent_node_map_parallel_cvisit_all[cvisit_all](ExecutionPolicy&& policy, F f) const; template bool xref:#concurrent_node_map_cvisit_while[visit_while](F f); template bool xref:#concurrent_node_map_cvisit_while[visit_while](F f) const; template bool xref:#concurrent_node_map_cvisit_while[cvisit_while](F f) const; template bool xref:#concurrent_node_map_parallel_cvisit_while[visit_while](ExecutionPolicy&& policy, F f); template bool xref:#concurrent_node_map_parallel_cvisit_while[visit_while](ExecutionPolicy&& policy, F f) const; template bool xref:#concurrent_node_map_parallel_cvisit_while[cvisit_while](ExecutionPolicy&& policy, F f) const; // capacity ++[[nodiscard]]++ bool xref:#concurrent_node_map_empty[empty]() const noexcept; size_type xref:#concurrent_node_map_size[size]() const noexcept; size_type xref:#concurrent_node_map_max_size[max_size]() const noexcept; // modifiers template bool xref:#concurrent_node_map_emplace[emplace](Args&&... args); bool xref:#concurrent_node_map_copy_insert[insert](const value_type& obj); bool xref:#concurrent_node_map_copy_insert[insert](const init_type& obj); bool xref:#concurrent_node_map_move_insert[insert](value_type&& obj); bool xref:#concurrent_node_map_move_insert[insert](init_type&& obj); template size_type xref:#concurrent_node_map_insert_iterator_range[insert](InputIterator first, InputIterator last); size_type xref:#concurrent_node_map_insert_initializer_list[insert](std::initializer_list il); insert_return_type xref:#concurrent_node_map_insert_node[insert](node_type&& nh); template bool xref:#concurrent_node_map_emplace_or_cvisit[emplace_or_visit](Args&&... args, F&& f); template bool xref:#concurrent_node_map_emplace_or_cvisit[emplace_or_cvisit](Args&&... args, F&& f); template bool xref:#concurrent_node_map_copy_insert_or_cvisit[insert_or_visit](const value_type& obj, F f); template bool xref:#concurrent_node_map_copy_insert_or_cvisit[insert_or_cvisit](const value_type& obj, F f); template bool xref:#concurrent_node_map_copy_insert_or_cvisit[insert_or_visit](const init_type& obj, F f); template bool xref:#concurrent_node_map_copy_insert_or_cvisit[insert_or_cvisit](const init_type& obj, F f); template bool xref:#concurrent_node_map_move_insert_or_cvisit[insert_or_visit](value_type&& obj, F f); template bool xref:#concurrent_node_map_move_insert_or_cvisit[insert_or_cvisit](value_type&& obj, F f); template bool xref:#concurrent_node_map_move_insert_or_cvisit[insert_or_visit](init_type&& obj, F f); template bool xref:#concurrent_node_map_move_insert_or_cvisit[insert_or_cvisit](init_type&& obj, F f); template size_type xref:#concurrent_node_map_insert_iterator_range_or_visit[insert_or_visit](InputIterator first, InputIterator last, F f); template size_type xref:#concurrent_node_map_insert_iterator_range_or_visit[insert_or_cvisit](InputIterator first, InputIterator last, F f); template size_type xref:#concurrent_node_map_insert_initializer_list_or_visit[insert_or_visit](std::initializer_list il, F f); template size_type xref:#concurrent_node_map_insert_initializer_list_or_visit[insert_or_cvisit](std::initializer_list il, F f); template insert_return_type xref:#concurrent_node_map_insert_node_or_visit[insert_or_visit](node_type&& nh, F f); template insert_return_type xref:#concurrent_node_map_insert_node_or_visit[insert_or_cvisit](node_type&& nh, F f); template bool xref:#concurrent_node_map_emplace_and_cvisit[emplace_and_visit](Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_emplace_and_cvisit[emplace_and_cvisit](Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_copy_insert_and_cvisit[insert_and_visit](const value_type& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_copy_insert_and_cvisit[insert_and_cvisit](const value_type& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_copy_insert_and_cvisit[insert_and_visit](const init_type& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_copy_insert_and_cvisit[insert_and_cvisit](const init_type& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_move_insert_and_cvisit[insert_and_visit](value_type&& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_move_insert_and_cvisit[insert_and_cvisit](value_type&& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_move_insert_and_cvisit[insert_and_visit](init_type&& obj, F1 f1, F2 f2); template bool xref:#concurrent_node_map_move_insert_and_cvisit[insert_and_cvisit](init_type&& obj, F1 f1, F2 f2); template size_type xref:#concurrent_node_map_insert_iterator_range_and_visit[insert_and_visit](InputIterator first, InputIterator last, F1 f1, F2 f2); template size_type xref:#concurrent_node_map_insert_iterator_range_and_visit[insert_and_cvisit](InputIterator first, InputIterator last, F1 f1, F2 f2); template size_type xref:#concurrent_node_map_insert_initializer_list_and_visit[insert_and_visit](std::initializer_list il, F1 f1, F2 f2); template size_type xref:#concurrent_node_map_insert_initializer_list_and_visit[insert_and_cvisit](std::initializer_list il, F1 f1, F2 f2); template insert_return_type xref:#concurrent_node_map_insert_node_and_visit[insert_and_visit](node_type&& nh, F1 f1, F2 f2); template insert_return_type xref:#concurrent_node_map_insert_node_and_visit[insert_and_cvisit](node_type&& nh, F1 f1, F2 f2); template bool xref:#concurrent_node_map_try_emplace[try_emplace](const key_type& k, Args&&... args); template bool xref:#concurrent_node_map_try_emplace[try_emplace](key_type&& k, Args&&... args); template bool xref:#concurrent_node_map_try_emplace[try_emplace](K&& k, Args&&... args); template bool xref:#concurrent_node_map_try_emplace_or_cvisit[try_emplace_or_visit](const key_type& k, Args&&... args, F&& f); template bool xref:#concurrent_node_map_try_emplace_or_cvisit[try_emplace_or_cvisit](const key_type& k, Args&&... args, F&& f); template bool xref:#concurrent_node_map_try_emplace_or_cvisit[try_emplace_or_visit](key_type&& k, Args&&... args, F&& f); template bool xref:#concurrent_node_map_try_emplace_or_cvisit[try_emplace_or_cvisit](key_type&& k, Args&&... args, F&& f); template bool xref:#concurrent_node_map_try_emplace_or_cvisit[try_emplace_or_visit](K&& k, Args&&... args, F&& f); template bool xref:#concurrent_node_map_try_emplace_or_cvisit[try_emplace_or_cvisit](K&& k, Args&&... args, F&& f); template bool xref:#concurrent_node_map_try_emplace_and_cvisit[try_emplace_and_visit](const key_type& k, Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_try_emplace_and_cvisit[try_emplace_and_cvisit](const key_type& k, Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_try_emplace_and_cvisit[try_emplace_and_visit](key_type&& k, Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_try_emplace_and_cvisit[try_emplace_and_cvisit](key_type&& k, Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_try_emplace_and_cvisit[try_emplace_and_visit](K&& k, Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_try_emplace_and_cvisit[try_emplace_and_cvisit](K&& k, Args&&... args, F1&& f1, F2&& f2); template bool xref:#concurrent_node_map_insert_or_assign[insert_or_assign](const key_type& k, M&& obj); template bool xref:#concurrent_node_map_insert_or_assign[insert_or_assign](key_type&& k, M&& obj); template bool xref:#concurrent_node_map_insert_or_assign[insert_or_assign](K&& k, M&& obj); size_type xref:#concurrent_node_map_erase[erase](const key_type& k); template size_type xref:#concurrent_node_map_erase[erase](const K& k); template size_type xref:#concurrent_node_map_erase_if_by_key[erase_if](const key_type& k, F f); template size_type xref:#concurrent_node_map_erase_if_by_key[erase_if](const K& k, F f); template size_type xref:#concurrent_node_map_erase_if[erase_if](F f); template void xref:#concurrent_node_map_parallel_erase_if[erase_if](ExecutionPolicy&& policy, F f); void xref:#concurrent_node_map_swap[swap](concurrent_node_map& other) noexcept(boost::allocator_traits::is_always_equal::value || boost::allocator_traits::propagate_on_container_swap::value); node_type xref:#concurrent_node_map_extract[extract](const key_type& k); template node_type xref:#concurrent_node_map_extract[extract](const K& k); template node_type xref:#concurrent_node_map_extract_if[extract_if](const key_type& k, F f); template node_type xref:#concurrent_node_map_extract[extract_if](const K& k, F f); void xref:#concurrent_node_map_clear[clear]() noexcept; template size_type xref:#concurrent_node_map_merge[merge](concurrent_node_map& source); template size_type xref:#concurrent_node_map_merge[merge](concurrent_node_map&& source); // observers hasher xref:#concurrent_node_map_hash_function[hash_function]() const; key_equal xref:#concurrent_node_map_key_eq[key_eq]() const; // map operations size_type xref:#concurrent_node_map_count[count](const key_type& k) const; template size_type xref:#concurrent_node_map_count[count](const K& k) const; bool xref:#concurrent_node_map_contains[contains](const key_type& k) const; template bool xref:#concurrent_node_map_contains[contains](const K& k) const; // bucket interface size_type xref:#concurrent_node_map_bucket_count[bucket_count]() const noexcept; // hash policy float xref:#concurrent_node_map_load_factor[load_factor]() const noexcept; float xref:#concurrent_node_map_max_load_factor[max_load_factor]() const noexcept; void xref:#concurrent_node_map_set_max_load_factor[max_load_factor](float z); size_type xref:#concurrent_node_map_max_load[max_load]() const noexcept; void xref:#concurrent_node_map_rehash[rehash](size_type n); void xref:#concurrent_node_map_reserve[reserve](size_type n); // statistics (if xref:concurrent_node_map_boost_unordered_enable_stats[enabled]) stats xref:#concurrent_node_map_get_stats[get_stats]() const; void xref:#concurrent_node_map_reset_stats[reset_stats]() noexcept; }; // Deduction Guides template>, class Pred = std::equal_to>, class Allocator = std::allocator>> concurrent_node_map(InputIterator, InputIterator, typename xref:#concurrent_node_map_deduction_guides[__see below__]::size_type = xref:#concurrent_node_map_deduction_guides[__see below__], Hash = Hash(), Pred = Pred(), Allocator = Allocator()) -> concurrent_node_map, xref:#concurrent_node_map_iter_mapped_type[__iter-mapped-type__], Hash, Pred, Allocator>; template, class Pred = std::equal_to, class Allocator = std::allocator>> concurrent_node_map(std::initializer_list>, typename xref:#concurrent_node_map_deduction_guides[__see below__]::size_type = xref:#concurrent_node_map_deduction_guides[__see below__], Hash = Hash(), Pred = Pred(), Allocator = Allocator()) -> concurrent_node_map; template concurrent_node_map(InputIterator, InputIterator, typename xref:#concurrent_node_map_deduction_guides[__see below__]::size_type, Allocator) -> concurrent_node_map, xref:#concurrent_node_map_iter_mapped_type[__iter-mapped-type__], boost::hash>, std::equal_to>, Allocator>; template concurrent_node_map(InputIterator, InputIterator, Allocator) -> concurrent_node_map, xref:#concurrent_node_map_iter_mapped_type[__iter-mapped-type__], boost::hash>, std::equal_to>, Allocator>; template concurrent_node_map(InputIterator, InputIterator, typename xref:#concurrent_node_map_deduction_guides[__see below__]::size_type, Hash, Allocator) -> concurrent_node_map, xref:#concurrent_node_map_iter_mapped_type[__iter-mapped-type__], Hash, std::equal_to>, Allocator>; template concurrent_node_map(std::initializer_list>, typename xref:#concurrent_node_map_deduction_guides[__see below__]::size_type, Allocator) -> concurrent_node_map, std::equal_to, Allocator>; template concurrent_node_map(std::initializer_list>, Allocator) -> concurrent_node_map, std::equal_to, Allocator>; template concurrent_node_map(std::initializer_list>, typename xref:#concurrent_node_map_deduction_guides[__see below__]::size_type, Hash, Allocator) -> concurrent_node_map, Allocator>; } // namespace unordered } // namespace boost ----- --- === Description *Template Parameters* [cols="1,1"] |=== |_Key_ .2+|`std::pair` must be https://en.cppreference.com/w/cpp/named_req/EmplaceConstructible[EmplaceConstructible^] into the table from any `std::pair` object convertible to it, and it also must be https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the table. |_T_ |_Hash_ |A unary function object type that acts a hash function for a `Key`. It takes a single argument of type `Key` and returns a value of type `std::size_t`. |_Pred_ |A binary function object that induces an equivalence relation on values of type `Key`. It takes two arguments of type `Key` and returns a value of type `bool`. |_Allocator_ |An allocator whose value type is the same as the table's value type. Allocators using https://en.cppreference.com/w/cpp/named_req/Allocator#Fancy_pointers[fancy pointers] are supported. |=== The element nodes of the table are held into an internal _bucket array_. An node is inserted into a bucket determined by the hash code of its element, but if the bucket is already occupied (a _collision_), an available one in the vicinity of the original position is used. The size of the bucket array can be automatically increased by a call to `insert`/`emplace`, or as a result of calling `rehash`/`reserve`. The _load factor_ of the table (number of elements divided by number of buckets) is never greater than `max_load_factor()`, except possibly for small sizes where the implementation may decide to allow for higher loads. If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]::value` is `true`, the hash function is used as-is; otherwise, a bit-mixing post-processing stage is added to increase the quality of hashing at the expense of extra computational cost. --- === Concurrency Requirements and Guarantees Concurrent invocations of `operator()` on the same const instance of `Hash` or `Pred` are required to not introduce data races. For `Alloc` being either `Allocator` or any allocator type rebound from `Allocator`, concurrent invocations of the following operations on the same instance `al` of `Alloc` are required to not introduce data races: * Copy construction from `al` of an allocator rebound from `Alloc` * `std::allocator_traits::allocate` * `std::allocator_traits::deallocate` * `std::allocator_traits::construct` * `std::allocator_traits::destroy` In general, these requirements on `Hash`, `Pred` and `Allocator` are met if these types are not stateful or if the operations only involve constant access to internal data members. With the exception of destruction, concurrent invocations of any operation on the same instance of a `concurrent_node_map` do not introduce data races — that is, they are thread-safe. If an operation *op* is explicitly designated as _blocking on_ `x`, where `x` is an instance of a `boost::concurrent_node_map`, prior blocking operations on `x` synchronize with *op*. So, blocking operations on the same `concurrent_node_map` execute sequentially in a multithreaded scenario. An operation is said to be _blocking on rehashing of_ ``__x__`` if it blocks on `x` only when an internal rehashing is issued. When executed internally by a `boost::concurrent_node_map`, the following operations by a user-provided visitation function on the element passed do not introduce data races: * Read access to the element. * Non-mutable modification of the element. * Mutable modification of the element: ** Within a container function accepting two visitation functions, always for the first function. ** Within a non-const container function whose name does not contain `cvisit`, for the last (or only) visitation function. Any `boost::concurrent_node_map operation` that inserts or modifies an element `e` synchronizes with the internal invocation of a visitation function on `e`. Visitation functions executed by a `boost::concurrent_node_map` `x` are not allowed to invoke any operation on `x`; invoking operations on a different `boost::concurrent_node_map` instance `y` is allowed only if concurrent outstanding operations on `y` do not access `x` directly or indirectly. --- === Configuration Macros ==== `BOOST_UNORDERED_DISABLE_REENTRANCY_CHECK` In debug builds (more precisely, when link:../../../../../assert/doc/html/assert.html#boost_assert_is_void[`BOOST_ASSERT_IS_VOID`^] is not defined), __container reentrancies__ (illegaly invoking an operation on `m` from within a function visiting elements of `m`) are detected and signalled through `BOOST_ASSERT_MSG`. When run-time speed is a concern, the feature can be disabled by globally defining this macro. --- ==== `BOOST_UNORDERED_ENABLE_STATS` Globally define this macro to enable xref:reference/stats.adoc#stats[statistics calculation] for the table. Note that this option decreases the overall performance of many operations. --- === Typedefs [source,c++,subs=+quotes] ---- typedef _implementation-defined_ node_type; ---- A class for holding extracted table elements, modelling https://en.cppreference.com/w/cpp/container/node_handle[NodeHandle]. --- [source,c++,subs=+quotes] ---- typedef _implementation-defined_ insert_return_type; ---- A specialization of an internal class template: [source,c++,subs=+quotes] ---- template struct _insert_return_type_ // name is exposition only { bool inserted; NodeType node; }; ---- with `NodeType` = `node_type`. --- === Constants ```cpp static constexpr size_type bulk_visit_size; ``` Chunk size internally used in xref:concurrent_node_map_bulk_visit[bulk visit] operations. --- === Constructors ==== Default Constructor ```c++ concurrent_node_map(); ``` Constructs an empty table using `hasher()` as the hash function, `key_equal()` as the key equality predicate and `allocator_type()` as the allocator. [horizontal] Postconditions:;; `size() == 0` Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Bucket Count Constructor ```c++ explicit concurrent_node_map(size_type n, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); ``` Constructs an empty table with at least `n` buckets, using `hf` as the hash function, `eql` as the key equality predicate, and `a` as the allocator. [horizontal] Postconditions:;; `size() == 0` Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Iterator Range Constructor [source,c++,subs="+quotes"] ---- template concurrent_node_map(InputIterator f, InputIterator l, size_type n = _implementation-defined_, const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); ---- Constructs an empty table with at least `n` buckets, using `hf` as the hash function, `eql` as the key equality predicate and `a` as the allocator, and inserts the elements from `[f, l)` into it. [horizontal] Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Copy Constructor ```c++ concurrent_node_map(concurrent_node_map const& other); ``` The copy constructor. Copies the contained elements, hash function, predicate and allocator. If `Allocator::select_on_container_copy_construction` exists and has the right signature, the allocator will be constructed from its result. [horizontal] Requires:;; `value_type` is copy constructible Concurrency:;; Blocking on `other`. --- ==== Move Constructor ```c++ concurrent_node_map(concurrent_node_map&& other); ``` The move constructor. The internal bucket array of `other` is transferred directly to the new table. The hash function, predicate and allocator are moved-constructed from `other`. If statistics are xref:concurrent_node_map_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` and calls `other.reset_stats()`. [horizontal] Concurrency:;; Blocking on `other`. --- ==== Iterator Range Constructor with Allocator ```c++ template concurrent_node_map(InputIterator f, InputIterator l, const allocator_type& a); ``` Constructs an empty table using `a` as the allocator, with the default hash function and key equality predicate and inserts the elements from `[f, l)` into it. [horizontal] Requires:;; `hasher`, `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Allocator Constructor ```c++ explicit concurrent_node_map(Allocator const& a); ``` Constructs an empty table, using allocator `a`. --- ==== Copy Constructor with Allocator ```c++ concurrent_node_map(concurrent_node_map const& other, Allocator const& a); ``` Constructs a table, copying ``other``'s contained elements, hash function, and predicate, but using allocator `a`. [horizontal] Concurrency:;; Blocking on `other`. --- ==== Move Constructor with Allocator ```c++ concurrent_node_map(concurrent_node_map&& other, Allocator const& a); ``` If `a == other.get_allocator()`, the elements of `other` are transferred directly to the new table; otherwise, elements are moved-constructed from those of `other`. The hash function and predicate are moved-constructed from `other`, and the allocator is copy-constructed from `a`. If statistics are xref:concurrent_node_map_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` iff `a == other.get_allocator()`, and always calls `other.reset_stats()`. [horizontal] Concurrency:;; Blocking on `other`. --- ==== Move Constructor from unordered_node_map ```c++ concurrent_node_map(unordered_node_map&& other); ``` Move construction from a xref:#unordered_node_map[`unordered_node_map`]. The internal bucket array of `other` is transferred directly to the new container. The hash function, predicate and allocator are moved-constructed from `other`. If statistics are xref:concurrent_node_map_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` and calls `other.reset_stats()`. [horizontal] Complexity:;; O(`bucket_count()`) --- ==== Initializer List Constructor [source,c++,subs="+quotes"] ---- concurrent_node_map(std::initializer_list il, size_type n = _implementation-defined_ const hasher& hf = hasher(), const key_equal& eql = key_equal(), const allocator_type& a = allocator_type()); ---- Constructs an empty table with at least `n` buckets, using `hf` as the hash function, `eql` as the key equality predicate and `a`, and inserts the elements from `il` into it. [horizontal] Requires:;; If the defaults are used, `hasher`, `key_equal` and `allocator_type` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Bucket Count Constructor with Allocator ```c++ concurrent_node_map(size_type n, allocator_type const& a); ``` Constructs an empty table with at least `n` buckets, using `hf` as the hash function, the default hash function and key equality predicate and `a` as the allocator. [horizontal] Postconditions:;; `size() == 0` Requires:;; `hasher` and `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Bucket Count Constructor with Hasher and Allocator ```c++ concurrent_node_map(size_type n, hasher const& hf, allocator_type const& a); ``` Constructs an empty table with at least `n` buckets, using `hf` as the hash function, the default key equality predicate and `a` as the allocator. [horizontal] Postconditions:;; `size() == 0` Requires:;; `key_equal` needs to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Iterator Range Constructor with Bucket Count and Allocator [source,c++,subs="+quotes"] ---- template concurrent_node_map(InputIterator f, InputIterator l, size_type n, const allocator_type& a); ---- Constructs an empty table with at least `n` buckets, using `a` as the allocator and default hash function and key equality predicate, and inserts the elements from `[f, l)` into it. [horizontal] Requires:;; `hasher`, `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== Iterator Range Constructor with Bucket Count and Hasher [source,c++,subs="+quotes"] ---- template concurrent_node_map(InputIterator f, InputIterator l, size_type n, const hasher& hf, const allocator_type& a); ---- Constructs an empty table with at least `n` buckets, using `hf` as the hash function, `a` as the allocator, with the default key equality predicate, and inserts the elements from `[f, l)` into it. [horizontal] Requires:;; `key_equal` needs to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== initializer_list Constructor with Allocator ```c++ concurrent_node_map(std::initializer_list il, const allocator_type& a); ``` Constructs an empty table using `a` and default hash function and key equality predicate, and inserts the elements from `il` into it. [horizontal] Requires:;; `hasher` and `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== initializer_list Constructor with Bucket Count and Allocator ```c++ concurrent_node_map(std::initializer_list il, size_type n, const allocator_type& a); ``` Constructs an empty table with at least `n` buckets, using `a` and default hash function and key equality predicate, and inserts the elements from `il` into it. [horizontal] Requires:;; `hasher` and `key_equal` need to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- ==== initializer_list Constructor with Bucket Count and Hasher and Allocator ```c++ concurrent_node_map(std::initializer_list il, size_type n, const hasher& hf, const allocator_type& a); ``` Constructs an empty table with at least `n` buckets, using `hf` as the hash function, `a` as the allocator and default key equality predicate,and inserts the elements from `il` into it. [horizontal] Requires:;; `key_equal` needs to be https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^]. --- === Destructor ```c++ ~concurrent_node_map(); ``` [horizontal] Note:;; The destructor is applied to every element, and all memory is deallocated --- === Assignment ==== Copy Assignment ```c++ concurrent_node_map& operator=(concurrent_node_map const& other); ``` The assignment operator. Destroys previously existing elements, copy-assigns the hash function and predicate from `other`, copy-assigns the allocator from `other` if `Alloc::propagate_on_container_copy_assignment` exists and `Alloc::propagate_on_container_copy_assignment::value` is `true`, and finally inserts copies of the elements of `other`. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^] Concurrency:;; Blocking on `*this` and `other`. --- ==== Move Assignment ```c++ concurrent_node_map& operator=(concurrent_node_map&& other) noexcept((boost::allocator_traits::is_always_equal::value || boost::allocator_traits::propagate_on_container_move_assignment::value) && std::is_same::value); ``` The move assignment operator. Destroys previously existing elements, swaps the hash function and predicate from `other`, and move-assigns the allocator from `other` if `Alloc::propagate_on_container_move_assignment` exists and `Alloc::propagate_on_container_move_assignment::value` is `true`. If at this point the allocator is equal to `other.get_allocator()`, the internal bucket array of `other` is transferred directly to `*this`; otherwise, inserts move-constructed copies of the elements of `other`. If statistics are xref:concurrent_node_map_boost_unordered_enable_stats[enabled], transfers the internal statistical information from `other` iff the final allocator is equal to `other.get_allocator()`, and always calls `other.reset_stats()`. [horizontal] Concurrency:;; Blocking on `*this` and `other`. --- ==== Initializer List Assignment ```c++ concurrent_node_map& operator=(std::initializer_list il); ``` Assign from values in initializer list. All previously existing elements are destroyed. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^] Concurrency:;; Blocking on `*this`. --- === Visitation ==== [c]visit ```c++ template size_t visit(const key_type& k, F f); template size_t visit(const key_type& k, F f) const; template size_t cvisit(const key_type& k, F f) const; template size_t visit(const K& k, F f); template size_t visit(const K& k, F f) const; template size_t cvisit(const K& k, F f) const; ``` If an element `x` exists with key equivalent to `k`, invokes `f` with a reference to `x`. Such reference is const iff `*this` is const. [horizontal] Returns:;; The number of elements visited (0 or 1). Notes:;; The `template` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. --- ==== Bulk visit ```c++ template size_t visit(FwdIterator first, FwdIterator last, F f); template size_t visit(FwdIterator first, FwdIterator last, F f) const; template size_t cvisit(FwdIterator first, FwdIterator last, F f) const; ``` For each element `k` in the range [`first`, `last`), if there is an element `x` in the container with key equivalent to `k`, invokes `f` with a reference to `x`. Such reference is const iff `*this` is const. Although functionally equivalent to individually invoking xref:concurrent_node_map_cvisit[`[c\]visit`] for each key, bulk visitation performs generally faster due to internal streamlining optimizations. It is advisable that `std::distance(first,last)` be at least xref:#concurrent_node_map_constants[`bulk_visit_size`] to enjoy a performance gain: beyond this size, performance is not expected to increase further. [horizontal] Requires:;; `FwdIterator` is a https://en.cppreference.com/w/cpp/named_req/ForwardIterator[LegacyForwardIterator^] ({cpp}11 to {cpp}17), or satisfies https://en.cppreference.com/w/cpp/iterator/forward_iterator[std::forward_iterator^] ({cpp}20 and later). For `K` = `std::iterator_traits::value_type`, either `K` is `key_type` or else `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. In the latter case, the library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. Returns:;; The number of elements visited. --- ==== [c]visit_all ```c++ template size_t visit_all(F f); template size_t visit_all(F f) const; template size_t cvisit_all(F f) const; ``` Successively invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. [horizontal] Returns:;; The number of elements visited. --- ==== Parallel [c]visit_all ```c++ template void visit_all(ExecutionPolicy&& policy, F f); template void visit_all(ExecutionPolicy&& policy, F f) const; template void cvisit_all(ExecutionPolicy&& policy, F f) const; ``` Invokes `f` with references to each of the elements in the table. Such references are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified. [horizontal] Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + These overloads only participate in overload resolution if `std::is_execution_policy_v>` is `true`. + + Unsequenced execution policies are not allowed. --- ==== [c]visit_while ```c++ template bool visit_while(F f); template bool visit_while(F f) const; template bool cvisit_while(F f) const; ``` Successively invokes `f` with references to each of the elements in the table until `f` returns `false` or all the elements are visited. Such references to the elements are const iff `*this` is const. [horizontal] Returns:;; `false` iff `f` ever returns `false`. --- ==== Parallel [c]visit_while ```c++ template bool visit_while(ExecutionPolicy&& policy, F f); template bool visit_while(ExecutionPolicy&& policy, F f) const; template bool cvisit_while(ExecutionPolicy&& policy, F f) const; ``` Invokes `f` with references to each of the elements in the table until `f` returns `false` or all the elements are visited. Such references to the elements are const iff `*this` is const. Execution is parallelized according to the semantics of the execution policy specified. [horizontal] Returns:;; `false` iff `f` ever returns `false`. Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + These overloads only participate in overload resolution if `std::is_execution_policy_v>` is `true`. + + Unsequenced execution policies are not allowed. + + Parallelization implies that execution does not necessary finish as soon as `f` returns `false`, and as a result `f` may be invoked with further elements for which the return value is also `false`. --- === Size and Capacity ==== empty ```c++ [[nodiscard]] bool empty() const noexcept; ``` [horizontal] Returns:;; `size() == 0` --- ==== size ```c++ size_type size() const noexcept; ``` [horizontal] Returns:;; The number of elements in the table. [horizontal] Notes:;; In the presence of concurrent insertion operations, the value returned may not accurately reflect the true size of the table right after execution. --- ==== max_size ```c++ size_type max_size() const noexcept; ``` [horizontal] Returns:;; `size()` of the largest possible table. --- === Modifiers ==== emplace ```c++ template bool emplace(Args&&... args); ``` Inserts an object, constructed with the arguments `args`, in the table if and only if there is no element in the table with an equivalent key. [horizontal] Requires:;; `value_type` is constructible from `args`. Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; If `args...` is of the form `k,v`, it delays constructing the whole object until it is certain that an element should be inserted, using only the `k` argument to check. --- ==== Copy Insert ```c++ bool insert(const value_type& obj); bool insert(const init_type& obj); ``` Inserts `obj` in the table if and only if there is no element in the table with an equivalent key. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; A call of the form `insert(x)`, where `x` is equally convertible to both `const value_type&` and `const init_type&`, is not ambiguous and selects the `init_type` overload. --- ==== Move Insert ```c++ bool insert(value_type&& obj); bool insert(init_type&& obj); ``` Inserts `obj` in the table if and only if there is no element in the table with an equivalent key. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; A call of the form `insert(x)`, where `x` is equally convertible to both `value_type&&` and `init_type&&`, is not ambiguous and selects the `init_type` overload. --- ==== Insert Iterator Range ```c++ template size_type insert(InputIterator first, InputIterator last); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- while(first != last) this->xref:#concurrent_node_map_emplace[emplace](*first++); ----- [horizontal] Returns:;; The number of elements inserted. --- ==== Insert Initializer List ```c++ size_type insert(std::initializer_list il); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- this->xref:#concurrent_node_map_insert_iterator_range[insert](il.begin(), il.end()); ----- [horizontal] Returns:;; The number of elements inserted. --- ==== Insert Node ```c++ insert_return_type insert(node_type&& nh); ``` If `nh` is not empty, inserts the associated element in the table if and only if there is no element in the table with a key equivalent to `nh.key()`. `nh` is empty when the function returns. [horizontal] Returns:;; An `insert_return_type` object constructed from `inserted` and `node`: + * If `nh` is empty, `inserted` is `false` and `node` is empty. * Otherwise if the insertion took place, `inserted` is true and `node` is empty. * If the insertion failed, `inserted` is false and `node` has the previous value of `nh`. Throws:;; If an exception is thrown by an operation other than a call to `hasher` the function has no effect. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; Behavior is undefined if `nh` is not empty and the allocators of `nh` and the container are not equal. --- ==== emplace_or_[c]visit ```c++ template bool emplace_or_visit(Args&&... args, F&& f); template bool emplace_or_cvisit(Args&&... args, F&& f); ``` Inserts an object, constructed with the arguments `args`, in the table if there is no element in the table with an equivalent key. Otherwise, invokes `f` with a reference to the equivalent element; such reference is const iff `emplace_or_cvisit` is used. [horizontal] Requires:;; `value_type` is constructible from `args`. Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; The interface is exposition only, as C++ does not allow to declare a parameter `f` after a variadic parameter pack. --- ==== Copy insert_or_[c]visit ```c++ template bool insert_or_visit(const value_type& obj, F f); template bool insert_or_cvisit(const value_type& obj, F f); template bool insert_or_visit(const init_type& obj, F f); template bool insert_or_cvisit(const init_type& obj, F f); ``` Inserts `obj` in the table if and only if there is no element in the table with an equivalent key. Otherwise, invokes `f` with a reference to the equivalent element; such reference is const iff a `*_cvisit` overload is used. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; In a call of the form `insert_or_[c]visit(obj, f)`, the overloads accepting a `const value_type&` argument participate in overload resolution only if `std::remove_cv::type>::type` is `value_type`. --- ==== Move insert_or_[c]visit ```c++ template bool insert_or_visit(value_type&& obj, F f); template bool insert_or_cvisit(value_type&& obj, F f); template bool insert_or_visit(init_type&& obj, F f); template bool insert_or_cvisit(init_type&& obj, F f); ``` Inserts `obj` in the table if and only if there is no element in the table with an equivalent key. Otherwise, invokes `f` with a reference to the equivalent element; such reference is const iff a `*_cvisit` overload is used. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; In a call of the form `insert_or_[c]visit(obj, f)`, the overloads accepting a `value_type&&` argument participate in overload resolution only if `std::remove_reference::type` is `value_type`. --- ==== Insert Iterator Range or Visit ```c++ template size_type insert_or_visit(InputIterator first, InputIterator last, F f); template size_type insert_or_cvisit(InputIterator first, InputIterator last, F f); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- while(first != last) this->xref:#concurrent_node_map_emplace_or_cvisit[emplace_or_[c\]visit](*first++, f); ----- [horizontal] Returns:;; The number of elements inserted. --- ==== Insert Initializer List or Visit ```c++ template size_type insert_or_visit(std::initializer_list il, F f); template size_type insert_or_cvisit(std::initializer_list il, F f); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- this->xref:#concurrent_node_map_insert_iterator_range_or_visit[insert_or_[c\]visit](il.begin(), il.end(), std::ref(f)); ----- [horizontal] Returns:;; The number of elements inserted. --- ==== Insert Node or Visit ```c++ template insert_return_type insert_or_visit(node_type&& nh, F f); template insert_return_type insert_or_cvisit(node_type&& nh, F f); ``` If `nh` is empty, does nothing. Otherwise, inserts the associated element in the table if and only if there is no element in the table with a key equivalent to `nh.key()`. Otherwise, invokes `f` with a reference to the equivalent element; such reference is const iff `insert_or_cvisit` is used. [horizontal] Returns:;; An `insert_return_type` object constructed from `inserted` and `node`: + * If `nh` is empty, `inserted` is `false` and `node` is empty. * Otherwise if the insertion took place, `inserted` is true and `node` is empty. * If the insertion failed, `inserted` is false and `node` has the previous value of `nh`. Throws:;; If an exception is thrown by an operation other than a call to `hasher` or call to `f`, the function has no effect. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; Behavior is undefined if `nh` is not empty and the allocators of `nh` and the container are not equal. --- ==== emplace_and_[c]visit ```c++ template bool emplace_and_visit(Args&&... args, F1&& f1, F2&& f2); template bool emplace_and_cvisit(Args&&... args, F1&& f1, F2&& f2); ``` Inserts an object, constructed with the arguments `args`, in the table if there is no element in the table with an equivalent key, and then invokes `f1` with a non-const reference to the newly created element. Otherwise, invokes `f2` with a reference to the equivalent element; such reference is const iff `emplace_and_cvisit` is used. [horizontal] Requires:;; `value_type` is constructible from `args`. Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; The interface is exposition only, as C++ does not allow to declare parameters `f1` and `f2` after a variadic parameter pack. --- ==== Copy insert_and_[c]visit ```c++ template bool insert_and_visit(const value_type& obj, F1 f1, F2 f2); template bool insert_and_cvisit(const value_type& obj, F1 f1, F2 f2); template bool insert_and_visit(const init_type& obj, F1 f1, F2 f2); template bool insert_and_cvisit(const init_type& obj, F1 f1, F2 f2); ``` Inserts `obj` in the table if and only if there is no element in the table with an equivalent key, and then invokes `f1` with a non-const reference to the newly created element. Otherwise, invokes `f2` with a reference to the equivalent element; such reference is const iff a `*_cvisit` overload is used. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/CopyInsertable[CopyInsertable^]. Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; In a call of the form `insert_and_[c]visit(obj, f1, f2)`, the overloads accepting a `const value_type&` argument participate in overload resolution only if `std::remove_cv::type>::type` is `value_type`. --- ==== Move insert_and_[c]visit ```c++ template bool insert_and_visit(value_type&& obj, F1 f1, F2 f2); template bool insert_and_cvisit(value_type&& obj, F1 f1, F2 f2); template bool insert_and_visit(init_type&& obj, F1 f1, F2 f2); template bool insert_and_cvisit(init_type&& obj, F1 f1, F2 f2); ``` Inserts `obj` in the table if and only if there is no element in the table with an equivalent key, and then invokes `f1` with a non-const reference to the newly created element. Otherwise, invokes `f2` with a reference to the equivalent element; such reference is const iff a `*_cvisit` overload is used. [horizontal] Requires:;; `value_type` is https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^]. Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; In a call of the form `insert_and_[c]visit(obj, f1, f2)`, the overloads accepting a `value_type&&` argument participate in overload resolution only if `std::remove_reference::type` is `value_type`. --- ==== Insert Iterator Range and Visit ```c++ template size_type insert_or_visit(InputIterator first, InputIterator last, F1 f1, F2 f2); template size_type insert_or_cvisit(InputIterator first, InputIterator last, F1 f2, F2 f2); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- while(first != last) this->xref:#concurrent_node_map_emplace_and_cvisit[emplace_and_[c\]visit](*first++, f1, f2); ----- [horizontal] Returns:;; The number of elements inserted. --- ==== Insert Initializer List and Visit ```c++ template size_type insert_and_visit(std::initializer_list il, F1 f1, F2 f2); template size_type insert_and_cvisit(std::initializer_list il, F1 f1, F2 f2); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- this->xref:#concurrent_node_map_insert_iterator_range_and_visit[insert_and_[c\]visit](il.begin(), il.end(), std::ref(f1), std::ref(f2)); ----- [horizontal] Returns:;; The number of elements inserted. --- ==== Insert Node and Visit ```c++ template insert_return_type insert_and_visit(node_type&& nh, F1 f1, F2 f2); template insert_return_type insert_and_cvisit(node_type&& nh, F1 f1, F2 f2); ``` If `nh` is empty, does nothing. Otherwise, inserts the associated element in the table if and only if there is no element in the table with a key equivalent to `nh.key()`, and then invokes `f1` with a non-const reference to the newly inserted element. Otherwise, invokes `f2` with a reference to the equivalent element; such reference is const iff `insert_or_cvisit` is used. [horizontal] Returns:;; An `insert_return_type` object constructed from `inserted` and `node`: + * If `nh` is empty, `inserted` is `false` and `node` is empty. * Otherwise if the insertion took place, `inserted` is true and `node` is empty. * If the insertion failed, `inserted` is false and `node` has the previous value of `nh`. Throws:;; If an exception is thrown by an operation other than a call to `hasher` or call to `f1` or `f2`, the function has no effect. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; Behavior is undefined if `nh` is not empty and the allocators of `nh` and the container are not equal. --- ==== try_emplace ```c++ template bool try_emplace(const key_type& k, Args&&... args); template bool try_emplace(key_type&& k, Args&&... args); template bool try_emplace(K&& k, Args&&... args); ``` Inserts an element constructed from `k` and `args` into the table if there is no existing element with key `k` contained within it. [horizontal] Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; This function is similiar to xref:#concurrent_node_map_emplace[emplace], with the difference that no `value_type` is constructed if there is an element with an equivalent key; otherwise, the construction is of the form: + + -- ```c++ // first two overloads value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(args)...)) // third overload value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(args)...)) ``` unlike xref:#concurrent_node_map_emplace[emplace], which simply forwards all arguments to ``value_type``'s constructor. The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. -- --- ==== try_emplace_or_[c]visit ```c++ template bool try_emplace_or_visit(const key_type& k, Args&&... args, F&& f); template bool try_emplace_or_cvisit(const key_type& k, Args&&... args, F&& f); template bool try_emplace_or_visit(key_type&& k, Args&&... args, F&& f); template bool try_emplace_or_cvisit(key_type&& k, Args&&... args, F&& f); template bool try_emplace_or_visit(K&& k, Args&&... args, F&& f); template bool try_emplace_or_cvisit(K&& k, Args&&... args, F&& f); ``` Inserts an element constructed from `k` and `args` into the table if there is no existing element with key `k` contained within it. Otherwise, invokes `f` with a reference to the equivalent element; such reference is const iff a `*_cvisit` overload is used. [horizontal] Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; No `value_type` is constructed if there is an element with an equivalent key; otherwise, the construction is of the form: + + -- ```c++ // first four overloads value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(args)...)) // last two overloads value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(args)...)) ``` The interface is exposition only, as C++ does not allow to declare a parameter `f` after a variadic parameter pack. The `template` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. -- --- ==== try_emplace_and_[c]visit ```c++ template bool try_emplace_and_visit(const key_type& k, Args&&... args, F1&& f1, F2&& f2); template bool try_emplace_and_cvisit(const key_type& k, Args&&... args, F1&& f1, F2&& f2); template bool try_emplace_and_visit(key_type&& k, Args&&... args, F1&& f1, F2&& f2); template bool try_emplace_and_cvisit(key_type&& k, Args&&... args, F1&& f1, F2&& f2); template bool try_emplace_and_visit(K&& k, Args&&... args, F1&& f1, F2&& f2); template bool try_emplace_and_cvisit(K&& k, Args&&... args, F1&& f1, F2&& f2); ``` Inserts an element constructed from `k` and `args` into the table if there is no existing element with key `k` contained within it, and then invokes `f1` with a non-const reference to the newly created element. Otherwise, invokes `f2` with a reference to the equivalent element; such reference is const iff a `*_cvisit` overload is used. [horizontal] Returns:;; `true` if an insert took place. + Concurrency:;; Blocking on rehashing of `*this`. Notes:;; No `value_type` is constructed if there is an element with an equivalent key; otherwise, the construction is of the form: + + -- ```c++ // first four overloads value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(args)...)) // last two overloads value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(args)...)) ``` The interface is exposition only, as C++ does not allow to declare parameter `f1` and `f2` after a variadic parameter pack. The `template` overloads only participate in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. -- --- ==== insert_or_assign ```c++ template bool insert_or_assign(const key_type& k, M&& obj); template bool insert_or_assign(key_type&& k, M&& obj); template bool insert_or_assign(K&& k, M&& obj); ``` Inserts a new element into the table or updates an existing one by assigning to the contained value. If there is an element with key `k`, then it is updated by assigning `std::forward(obj)`. If there is no such element, it is added to the table as: ```c++ // first two overloads value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(obj))) // third overload value_type(std::piecewise_construct, std::forward_as_tuple(std::forward(k)), std::forward_as_tuple(std::forward(obj))) ``` [horizontal] Returns:;; `true` if an insert took place. Concurrency:;; Blocking on rehashing of `*this`. Notes:;; The `template` only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. --- ==== erase ```c++ size_type erase(const key_type& k); template size_type erase(const K& k); ``` Erases the element with key equivalent to `k` if it exists. [horizontal] Returns:;; The number of elements erased (0 or 1). Throws:;; Only throws an exception if it is thrown by `hasher` or `key_equal`. Notes:;; The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. --- ==== erase_if by Key ```c++ template size_type erase_if(const key_type& k, F f); template size_type erase_if(const K& k, F f); ``` Erases the element `x` with key equivalent to `k` if it exists and `f(x)` is `true`. [horizontal] Returns:;; The number of elements erased (0 or 1). Throws:;; Only throws an exception if it is thrown by `hasher`, `key_equal` or `f`. Notes:;; `f` is passed a non-const reference to `x`. + + The `template` overload only participates in overload resolution if `std::is_execution_policy_v>` is `false`. + + The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. --- ==== erase_if ```c++ template size_type erase_if(F f); ``` Successively invokes `f` with non-const references to each of the elements in the table, and erases those for which `f` returns `true`. [horizontal] Returns:;; The number of elements erased. Throws:;; Only throws an exception if it is thrown by `f`. --- ==== Parallel erase_if ```c++ template void erase_if(ExecutionPolicy&& policy, F f); ``` Invokes `f` with non-const references to each of the elements in the table, and erases those for which `f` returns `true`. Execution is parallelized according to the semantics of the execution policy specified. [horizontal] Throws:;; Depending on the exception handling mechanism of the execution policy used, may call `std::terminate` if an exception is thrown within `f`. Notes:;; Only available in compilers supporting C++17 parallel algorithms. + + This overload only participates in overload resolution if `std::is_execution_policy_v>` is `true`. + + Unsequenced execution policies are not allowed. --- ==== swap ```c++ void swap(concurrent_node_map& other) noexcept(boost::allocator_traits::is_always_equal::value || boost::allocator_traits::propagate_on_container_swap::value); ``` Swaps the contents of the table with the parameter. If `Allocator::propagate_on_container_swap` is declared and `Allocator::propagate_on_container_swap::value` is `true` then the tables' allocators are swapped. Otherwise, swapping with unequal allocators results in undefined behavior. [horizontal] Throws:;; Nothing unless `key_equal` or `hasher` throw on swapping. Concurrency:;; Blocking on `*this` and `other`. --- ==== extract ```c++ node_type extract(const key_type& k); template node_type extract(K&& k); ``` Extracts the element with key equivalent to `k`, if it exists. [horizontal] Returns:;; A `node_type` object holding the extracted element, or empty if no element was extracted. Throws:;; Only throws an exception if it is thrown by `hasher` or `key_equal`. Notes:;; The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. --- ==== extract_if ```c++ template node_type extract_if(const key_type& k, F f); template node_type extract_if(K&& k, F f); ``` Extracts the element `x` with key equivalent to `k`, if it exists and `f(x)` is `true`. [horizontal] Returns:;; A `node_type` object holding the extracted element, or empty if no element was extracted. Throws:;; Only throws an exception if it is thrown by `hasher` or `key_equal` or `f`. Notes:;; The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. --- ==== clear ```c++ void clear() noexcept; ``` Erases all elements in the table. [horizontal] Postconditions:;; `size() == 0`, `max_load() >= max_load_factor() * bucket_count()` Concurrency:;; Blocking on `*this`. --- ==== merge ```c++ template size_type merge(concurrent_node_map& source); template size_type merge(concurrent_node_map&& source); ``` Move-inserts all the elements from `source` whose key is not already present in `*this`, and erases them from `source`. [horizontal] Returns:;; The number of elements inserted. Concurrency:;; Blocking on `*this` and `source`. --- === Observers ==== get_allocator ``` allocator_type get_allocator() const noexcept; ``` [horizontal] Returns:;; The table's allocator. --- ==== hash_function ``` hasher hash_function() const; ``` [horizontal] Returns:;; The table's hash function. --- ==== key_eq ``` key_equal key_eq() const; ``` [horizontal] Returns:;; The table's key equality predicate. --- === Map Operations ==== count ```c++ size_type count(const key_type& k) const; template size_type count(const K& k) const; ``` [horizontal] Returns:;; The number of elements with key equivalent to `k` (0 or 1). Notes:;; The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. + + In the presence of concurrent insertion operations, the value returned may not accurately reflect the true state of the table right after execution. --- ==== contains ```c++ bool contains(const key_type& k) const; template bool contains(const K& k) const; ``` [horizontal] Returns:;; A boolean indicating whether or not there is an element with key equal to `k` in the table. Notes:;; The `template` overload only participates in overload resolution if `Hash::is_transparent` and `Pred::is_transparent` are valid member typedefs. The library assumes that `Hash` is callable with both `K` and `Key` and that `Pred` is transparent. This enables heterogeneous lookup which avoids the cost of instantiating an instance of the `Key` type. + + In the presence of concurrent insertion operations, the value returned may not accurately reflect the true state of the table right after execution. --- === Bucket Interface ==== bucket_count ```c++ size_type bucket_count() const noexcept; ``` [horizontal] Returns:;; The size of the bucket array. --- === Hash Policy ==== load_factor ```c++ float load_factor() const noexcept; ``` [horizontal] Returns:;; `static_cast(size())/static_cast(bucket_count())`, or `0` if `bucket_count() == 0`. --- ==== max_load_factor ```c++ float max_load_factor() const noexcept; ``` [horizontal] Returns:;; Returns the table's maximum load factor. --- ==== Set max_load_factor ```c++ void max_load_factor(float z); ``` [horizontal] Effects:;; Does nothing, as the user is not allowed to change this parameter. Kept for compatibility with `boost::unordered_map`. --- ==== max_load ```c++ size_type max_load() const noexcept; ``` [horizontal] Returns:;; The maximum number of elements the table can hold without rehashing, assuming that no further elements will be erased. Note:;; After construction, rehash or clearance, the table's maximum load is at least `max_load_factor() * bucket_count()`. This number may decrease on erasure under high-load conditions. + + In the presence of concurrent insertion operations, the value returned may not accurately reflect the true state of the table right after execution. --- ==== rehash ```c++ void rehash(size_type n); ``` Changes if necessary the size of the bucket array so that there are at least `n` buckets, and so that the load factor is less than or equal to the maximum load factor. When applicable, this will either grow or shrink the `bucket_count()` associated with the table. When `size() == 0`, `rehash(0)` will deallocate the underlying buckets array. [horizontal] Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the table's hash function or comparison function. Concurrency:;; Blocking on `*this`. --- ==== reserve ```c++ void reserve(size_type n); ``` Equivalent to `a.rehash(ceil(n / a.max_load_factor()))`. Similar to `rehash`, this function can be used to grow or shrink the number of buckets in the table. [horizontal] Throws:;; The function has no effect if an exception is thrown, unless it is thrown by the table's hash function or comparison function. Concurrency:;; Blocking on `*this`. --- === Statistics ==== get_stats ```c++ stats get_stats() const; ``` [horizontal] Returns:;; A statistical description of the insertion and lookup operations performed by the table so far. Notes:;; Only available if xref:reference/stats.adoc#stats[statistics calculation] is xref:concurrent_node_map_boost_unordered_enable_stats[enabled]. --- ==== reset_stats ```c++ void reset_stats() noexcept; ``` [horizontal] Effects:;; Sets to zero the internal statistics kept by the table. Notes:;; Only available if xref:reference/stats.adoc#stats[statistics calculation] is xref:concurrent_node_map_boost_unordered_enable_stats[enabled]. --- === Deduction Guides A deduction guide will not participate in overload resolution if any of the following are true: - It has an `InputIterator` template parameter and a type that does not qualify as an input iterator is deduced for that parameter. - It has an `Allocator` template parameter and a type that does not qualify as an allocator is deduced for that parameter. - It has a `Hash` template parameter and an integral type or a type that qualifies as an allocator is deduced for that parameter. - It has a `Pred` template parameter and a type that qualifies as an allocator is deduced for that parameter. A `size_­type` parameter type in a deduction guide refers to the `size_­type` member type of the table type deduced by the deduction guide. Its default value coincides with the default value of the constructor selected. ==== __iter-value-type__ [listings,subs="+macros,+quotes"] ----- template using __iter-value-type__ = typename std::iterator_traits::value_type; // exposition only ----- ==== __iter-key-type__ [listings,subs="+macros,+quotes"] ----- template using __iter-key-type__ = std::remove_const_t< std::tuple_element_t<0, xref:#concurrent_node_map_iter_value_type[__iter-value-type__]>>; // exposition only ----- ==== __iter-mapped-type__ [listings,subs="+macros,+quotes"] ----- template using __iter-mapped-type__ = std::tuple_element_t<1, xref:#concurrent_node_map_iter_value_type[__iter-value-type__]>; // exposition only ----- ==== __iter-to-alloc-type__ [listings,subs="+macros,+quotes"] ----- template using __iter-to-alloc-type__ = std::pair< std::add_const_t>>, std::tuple_element_t<1, xref:#concurrent_node_map_iter_value_type[__iter-value-type__]>>; // exposition only ----- === Equality Comparisons ==== operator== ```c++ template bool operator==(const concurrent_node_map& x, const concurrent_node_map& y); ``` Returns `true` if `x.size() == y.size()` and for every element in `x`, there is an element in `y` with the same key, with an equal value (using `operator==` to compare the value types). [horizontal] Concurrency:;; Blocking on `x` and `y`. Notes:;; Behavior is undefined if the two tables don't have equivalent equality predicates. --- ==== operator!= ```c++ template bool operator!=(const concurrent_node_map& x, const concurrent_node_map& y); ``` Returns `false` if `x.size() == y.size()` and for every element in `x`, there is an element in `y` with the same key, with an equal value (using `operator==` to compare the value types). [horizontal] Concurrency:;; Blocking on `x` and `y`. Notes:;; Behavior is undefined if the two tables don't have equivalent equality predicates. --- === Swap ```c++ template void swap(concurrent_node_map& x, concurrent_node_map& y) noexcept(noexcept(x.swap(y))); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- x.xref:#concurrent_node_map_swap[swap](y); ----- --- === erase_if ```c++ template typename concurrent_node_map::size_type erase_if(concurrent_node_map& c, Predicate pred); ``` Equivalent to [listing,subs="+macros,+quotes"] ----- c.xref:#concurrent_node_map_erase_if[erase_if](pred); ----- === Serialization ``concurrent_node_map``s can be archived/retrieved by means of link:../../../../../serialization/index.html[Boost.Serialization^] using the API provided by this library. Both regular and XML archives are supported. ==== Saving an concurrent_node_map to an archive Saves all the elements of a `concurrent_node_map` `x` to an archive (XML archive) `ar`. [horizontal] Requires:;; `std::remove_const::type` and `std::remove_const::type` are serializable (XML serializable), and they do support Boost.Serialization `save_construct_data`/`load_construct_data` protocol (automatically suported by https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[DefaultConstructible^] types). Concurrency:;; Blocking on `x`. --- ==== Loading an concurrent_node_map from an archive Deletes all preexisting elements of a `concurrent_node_map` `x` and inserts from an archive (XML archive) `ar` restored copies of the elements of the original `concurrent_node_map` `other` saved to the storage read by `ar`. [horizontal] Requires:;; `x.key_equal()` is functionally equivalent to `other.key_equal()`. Concurrency:;; Blocking on `x`.