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and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
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[#concurrent_flat_set]
[#concurrent_flat_set]
Class Template concurrent_flat_set
类模板 concurrent++_++flat++_++set
:idprefix: concurrent_flat_set_
:idprefix: concurrent_flat_set_
`boost::concurrent_flat_set` — A hash table that stores unique values and allows for concurrent element insertion, erasure, lookup and access without external synchronization mechanisms.
`boost::concurrent++_++flat++_++set` —— 一种存储唯一值的哈希表，它支持并发的元素插入、删除、查找及访问操作，且无需外部同步机制。
Even though it acts as a container, `boost::concurrent_flat_set` 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 is done through user-provided _visitation functions_ that are passed to `concurrent_flat_set` operations where they are executed internally in a controlled fashion. Such visitation-based API allows for low-contention concurrent usage scenarios.
尽管 `boost::concurrent++_++flat++_++set` 具备容器特性，但它并不符合 C{plus}{plus}标准中的 https://en.cppreference.com/w/cpp/named_req/Container[容器] 概念。具体而言，该容器未提供迭代器及相关操作（如 `begin` 、 `end` 等）。元素访问通过用户提供的__访问函数__实现，这些函数被传递至 `concurrent++_++flat++_++set` 操作中，并在其内部以受控方式执行。这种基于访问机制的 API 设计能够有效支持低争用的并发应用场景。
The internal data structure of `boost::concurrent_flat_set` is similar to that of `boost::unordered_flat_set`. As a result of its using open-addressing techniques, `value_type` must be move-constructible and pointer stability is not kept under rehashing.
`boost::concurrent++_++flat++_++set` 的内部数据结构类似于 `boost::unordered++_++flat++_++set` 。由于其采用开放寻址技术， `value++_++type` 必须满足可移动构造要求，且在重哈希过程中无法保持指针稳定性。
Synopsis
概要
:279
---
---
Description
描述
*Template Parameters*
*模板参数*
_Key_
_键_
`Key` must be https://en.cppreference.com/w/cpp/named_req/MoveInsertable[MoveInsertable^] into the container
Key 必须满足
and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
https://en.cppreference.com/w/cpp/named_req/MoveInsertable[可移动插入] 到容器中的要求，且需满足从容器中 https://en.cppreference.com/w/cpp/named_req/Erasable[可擦除] 的要求。
_Hash_
_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`.
一种为`Key`提供哈希功能的一元函数对象类型。它接受单个`Key`类型参数，并返回`std::size_t`类型的值。
_Pred_
_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`.
一种二元函数对象，用于在Key类型的值上构建等价关系。它接受两个Key类型的参数，并返回一个bool类型的值。
_Allocator_
_Allocator_
An allocator whose value type is the same as the table's value type.
值类型与该表的值类型相同的分配器。
`std::allocator_traits<Allocator>::pointer` and `std::allocator_traits<Allocator>::const_pointer` must be convertible to/from `value_type*` and `const value_type*`, respectively.
`std::allocator_traits<allocator>::pointer` 与 `std::allocator_traits<allocator>::const_pointer` 必须分别可与 `value_type*` 和 `const value_type*` 相互转换。</allocator></allocator>
The elements of the table are held into an internal _bucket array_. An element is inserted into a bucket determined by its hash code, but if the bucket is already occupied (a _collision_), an available one in the vicinity of the original position is used.
容器的元素存储在内部的桶数组中。元素根据其哈希值被插入到对应的桶中，若该桶已被占用（即发生哈希冲突），则使用原位置附近的可用桶。
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.
调用 `insert`/`emplace` 或执行 `rehash`/`reserve` 操作时，桶数组的大小会自动扩容。容器的负载因子（元素数量除以桶数量）永远不会超过 `max_load_factor()`，仅在尺寸较小时，实现可能允许更高的负载因子。
If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::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.
若 `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<hash>::value` 为 `true`，则哈希函数直接使用；否则会添加一个位混合后处理阶段，以额外的计算开销为代价提升哈希质量。</hash>
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---
---
Concurrency Requirements and Guarantees
并发要求与保证
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:
要求对同一 `Hash` 或 `Pred` 常量实例并发调用 `operator()` 时不得引入数据竞争。对于 `Alloc` （即 `Allocator` 或其重绑定后的任意分配器类型），在同一实例 `al` 上并发调用以下操作时不得引入数据竞争：
Copy construction from `al` of an allocator rebound from `Alloc`
通过从`Alloc`重新绑定的分配器以`al`进行拷贝构造
`std::allocator_traits<Alloc>::allocate`
`std::allocator_traits<alloc>::allocate`</alloc>
English Chinese (Simplified Han script) Actions
Statistics
统计信息
get_stats
get_stats
```c++ stats get_stats() const; ```
```c++ stats get_stats() const; ```
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_flat_set_boost_unordered_enable_stats[enabled].
返回值：;; 该哈希表迄今为止执行的插入与查找操作的统计信息。
备注：;; 仅当 xref:reference/stats.adoc#stats[统计计算] 被 xref:concurrent_flat_set_boost_unordered_enable_stats[启用] 时，本接口方可使用。
```c++ template<class K, class H, class P, class A, class Predicate> typename concurrent_flat_set<K, H, P, A>::size_type erase_if(concurrent_flat_set<K, H, P, A>& c, Predicate pred); ```
```c++ template<class k,="" class="" h,="" p,="" a,="" predicate=""> typename concurrent_flat_set<k, h,="" p,="" a="">::size_type erase_if(concurrent_flat_set<k, h,="" p,="" a="">&amp; c, Predicate pred); ```</k,></k,></class>
Serialization
序列化
Saving an concurrent_flat_set to an archive
将 concurrent++_++flat++_++set 保存到归档
Requires:;; `value_type` is serializable (XML serializable), and it supports 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`.
要求;; `value++_++type` 必须可序列化（支持 XML 序列化），且需要支持 Boost.Serialization 的 `save++_++construct++_++data` / `load++_++construct++_++data` 协议（该协议自动支持满足 https://en.cppreference.com/w/cpp/named_req/DefaultConstructible[可默认构造] 要求的类型）。 并发性;; 阻塞于 `x` 。
`std::allocator_traits<Alloc>::deallocate`
`std::allocator_traits<alloc>::deallocate`</alloc>
Returns:;; The number of elements in the table.
返回值：;; 哈希表中的元素总数。
Notes:;; In the presence of concurrent insertion operations, the value returned may not accurately reflect the true size of the table right after execution.
注意：;; 在存在并发插入操作时，返回的值可能无法准确反映函数执行后哈希表的真实大小。
max_size
max_size
```c++ concurrent_flat_set(std::initializer_list<value_type> il, const allocator_type& a); ```
```c++ concurrent_flat_set(std::initializer_list<value_type> il, const allocator_type&amp; a); ```</value_type>
The internal data structure of `boost::concurrent_flat_set` is similar to that of `boost::unordered_flat_set`. As a result of its using open-addressing techniques, `value_type` must be move-constructible and pointer stability is not kept under rehashing.
`boost::concurrent++_++flat++_++set` 的内部数据结构类似于 `boost::unordered++_++flat++_++set` 。由于其采用开放寻址技术， `value++_++type` 必须满足可移动构造要求，且在重哈希过程中无法保持指针稳定性。
*Template Parameters*
*模板参数*
and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
https://en.cppreference.com/w/cpp/named_req/MoveInsertable[可移动插入] 到容器中的要求，且需满足从容器中 https://en.cppreference.com/w/cpp/named_req/Erasable[可擦除] 的要求。
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`.
一种为`Key`提供哈希功能的一元函数对象类型。它接受单个`Key`类型参数，并返回`std::size_t`类型的值。
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`.
一种二元函数对象，用于在Key类型的值上构建等价关系。它接受两个Key类型的参数，并返回一个bool类型的值。
An allocator whose value type is the same as the table's value type.
值类型与该表的值类型相同的分配器。
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.
调用 `insert`/`emplace` 或执行 `rehash`/`reserve` 操作时，桶数组的大小会自动扩容。容器的负载因子（元素数量除以桶数量）永远不会超过 `max_load_factor()`，仅在尺寸较小时，实现可能允许更高的负载因子。
If `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<Hash>::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.
若 `link:../../../../../container_hash/doc/html/hash.html#ref_hash_is_avalanchinghash[hash_is_avalanching]<hash>::value` 为 `true`，则哈希函数直接使用；否则会添加一个位混合后处理阶段，以额外的计算开销为代价提升哈希质量。</hash>
Concurrency Requirements and Guarantees
并发要求与保证
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.
构造一个至少包含 `n` 个桶的空容器，使用 `hf` 作为哈希函数、 `eql` 作为键相等性谓词、 `a` 作为分配器，并将 `++[++f, l)` 范围内的元素插入其中。
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:
要求对同一 `Hash` 或 `Pred` 常量实例并发调用 `operator()` 时不得引入数据竞争。对于 `Alloc` （即 `Allocator` 或其重绑定后的任意分配器类型），在同一实例 `al` 上并发调用以下操作时不得引入数据竞争：
Copy construction from `al` of an allocator rebound from `Alloc`
通过从`Alloc`重新绑定的分配器以`al`进行拷贝构造
`std::allocator_traits<Alloc>::allocate`
`std::allocator_traits<alloc>::allocate`</alloc>
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.
通常而言，若 `Hash` 、 `Pred` 和 `Allocator` 这些类型不包含状态，或其操作仅涉及对内部数据成员的常量访问，即可满足上述要求。
With the exception of destruction, concurrent invocations of any operation on the same instance of a `concurrent_flat_set` do not introduce data races — that is, they are thread-safe.
除析构操作外，对同一个 `concurrent++_++flat++_++set` 实例并发调用任何操作都不会引发数据竞争——即这些操作是线程安全的。
If an operation *op* is explicitly designated as _blocking on_ `x`, where `x` is an instance of a `boost::concurrent_flat_set`, prior blocking operations on `x` synchronize with *op*. So, blocking operations on the same `concurrent_flat_set` execute sequentially in a multithreaded scenario.
若操作 *op* 显式指定为__阻塞于__ 容器 `x` （其中 `x` 是 `boost::concurrent++_++flat++_++set` 的实例），则先前对 `x` 的阻塞操作将与 *op* 同步。因此，在多线程场景下，对同一 `concurrent++_++flat++_++set` 的阻塞操作将按顺序执行。
An operation is said to be _blocking on rehashing of_ ``__x__`` if it blocks on `x` only when an internal rehashing is issued.
若某个操作仅在触发内部重哈希时才会阻塞于 _`x`_，则称该操作__阻塞于 _`x`_ 的重哈希过程__。

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and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.MoveInsertable[可移动插入] 到容器中的要求，且需满足从容器中 https://en.cppreference.com/w/cpp/named_req/Erasable[可擦除] 的要求。
06/05/2026
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String added in the repository
and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
and https://en.cppreference.com/w/cpp/named_req/Erasable[Erasable^] from the container.
06/05/2026
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String information

Flags
safe-html, strict-same
Unit identifier
50156
Source string location
:290
String age
06/05/2026
Last updated
06/06/2026
Source string age
06/05/2026
Translation file AsciiDoc file
doc/modules/ROOT/pages/reference/concurrent_flat_set_zh_Hans.adoc, string 13