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The value of the insertion counter for the initial group in the probe
A read-write spinlock for synchronized access to any element in the group. ** An atomic _insertion counter_ used for optimistic insertion as described below.探测起始组的插入计数器值
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Insertion uses the following _optimistic algorithm_:
sequence is locally recorded (let's call this value `c0`).插入操作使用以下 _乐观算法_：
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By using atomic operations to access the group metadata, lookup is (group-level) lock-free up to the point where an actual comparison needs to be done with an element that has been previously SIMD-matched: only then is the group's spinlock used.
Insertion uses the following _optimistic algorithm_:通过使用原子操作访问组元数据，查找操作在（组级别）上是无锁的，直到需要与实际进行 SIMD 匹配的元素进行比较时才会使用组的自旋锁。
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** A read-write spinlock for synchronized access to any element in the group. ** An atomic _insertion counter_ used for optimistic insertion as described below.
By using atomic operations to access the group metadata, lookup is (group-level) lock-free up to the point where an actual comparison needs to be done with an element that has been previously SIMD-matched: only then is the group's spinlock used.- 一个读写自旋锁，用于同步对组内任何元素的访问。
- 一个原子 _插入计数器_，用于下文所述的乐观插入。
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Group level: Each 15-slot group is equipped with an 8-byte word containing:
Group level: Each 15-slot group is equipped with an 8-byte word containing:组级：每个包含15个槽位的组都配备一个8字节的字，其中包含：
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to the container. Typically, such access is in read mode (that is, concurrent) even for modifying operations, so for most practical purposes there is no thread contention at this level. Access is only in write mode (blocking) when rehashing or performing container-wide operations such as swapping or assignment.
to the container. Typically, such access is in read mode (that is, concurrent) even for modifying operations, so for most practical purposes there is no thread contention at this level. Access is only in write mode (blocking) when rehashing or performing container-wide operations such as swapping or assignment.对容器的访问。通常情况下，即使是修改操作，此类访问也处于读模式（即并发的），因此在实际使用中，此层面几乎不会发生线程争用。仅在重哈希或执行交换、赋值等容器级操作时，访问才会处于写模式（阻塞）。
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Container level: A read-write mutex is used to control access from any operation
Container level: A read-write mutex is used to control access from any operation容器层面：使用读写互斥锁来控制来自任何操作的访问。
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Two levels of synchronization are used:
Two levels of synchronization are used:采用两级同步机制：
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image::cfoa.png[align=center]
image::cfoa.png[align=center]
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`boost::concurrent_flat_set`/`boost::concurrent_node_set` and `boost::concurrent_flat_map`/`boost::concurrent_node_map` use the basic xref:structures.adoc#structures_open_addressing_containers[open-addressing layout] described above augmented with synchronization mechanisms.
`boost::concurrent_flat_set`/`boost::concurrent_node_set` and和 `boost::concurrent_flat_map`/`boost::concurrent_node_map` use the basic使用了上述基本的 xref:structures.adoc#structures_open_addressing_containers[open-addressing layout] described above augmented with synchronization mechanisms.开放寻址布局]，并增加了同步机制。
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Concurrent Containers
Concurrent Containers并发容器
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A more detailed description of Boost.Unordered's open-addressing implementation is given in an https://bannalia.blogspot.com/2022/11/inside-boostunorderedflatmap.html[external article]. For more information on implementation rationale, read the xref:rationale.adoc#rationale_open_addresing_containers[corresponding section].
A more detailed description of Boost.Unordered's open-addressing implementation is given in an https://bannalia.blogspot.com/2022/11/inside-boostunorderedflatmap.html[external article]. For more information on implementation rationale, read the关于 Boost.Unordered 开放寻址实现的更详细描述，请参阅 https://bannalia.blogspot.com/2022/11/inside-boostunorderedflatmap.html[外部文章]。有关实现原理的更多信息，请阅读 xref:rationale.adoc#rationale_open_addresing_containers[corresponding section].相应章节]。
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image::foa-metadata-interleaving.png[align=center]
image::foa-metadata-interleaving.png[align=center]
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In architectures without SIMD support, the logical layout stays the same, but the metadata word is codified using a technique we call _bit interleaving_: this layout allows us to emulate SIMD with reasonably good performance using only standard arithmetic and logical operations.
In architectures without SIMD support, the logical layout stays the same, but the metadata word is codified using a technique we call _bit interleaving_: this layout allows us to emulate SIMD with reasonably good performance using only standard arithmetic and logical operations.在不支持 SIMD 的架构中，逻辑布局保持不变，但元数据字采用一种称为 _位交错_ 的技术进行编码：这种布局允许我们仅使用标准算术和逻辑运算，以相当不错的性能来模拟 SIMD。
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Insertion is algorithmically similar: empty buckets are located using SIMD, and when going past a full group its corresponding overflow bit is set to 1.
Insertion is algorithmically similar: empty buckets are located using SIMD, and when going past a full group its corresponding overflow bit is set to 1.插入操作的算法逻辑类似：通过 SIMD 技术定位空桶，当遍历到已满的组时，会将其对应的溢出位设置为 1。
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- If the bit in the position _h_ mod 8 is zero, lookup terminates (and the element is not present). - If the bit is set to 1 (the group has been _overflowed_), further groups are checked using https://en.wikipedia.org/wiki/Quadratic_probing[_quadratic probing_], and the process is repeated.
- If the bit in the position _h_ mod 8 is zero, lookup terminates (and the element is not present). - If the bit is set to 1 (the group has been _overflowed_), further groups are checked using若位置 _h_ mod 8 的比特位为零，则查找终止（确认元素不存在）。 元素不存在）。 - 若该比特位为1（表示该组已__溢出__），则通过 https://en.wikipedia.org/wiki/Quadratic_probing[_quadratic probing_], and the process is repeated.二次探查法_] 检查后续组，并重复此过程。
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When looking for an element with hash value _h_, SIMD technologies such as https://en.wikipedia.org/wiki/SSE2[SSE2] and https://en.wikipedia.org/wiki/ARM_architecture_family#Advanced_SIMD_(Neon)[Neon] allow us to very quickly inspect the full metadata word and look for the reduced value of _h_ among all the 15 buckets with just a handful of CPU instructions: non-matching buckets can be readily discarded, and those whose reduced hash value matches need be inspected via full comparison with the corresponding element. If the looked-for element is not present, the overflow byte is inspected:
When looking for an element with hash value _h_, SIMD technologies such as当查找一个哈希值为 _h_ 的元素时，可以使用诸如 https://en.wikipedia.org/wiki/SSE2[SSE2] and和 https://en.wikipedia.org/wiki/ARM_architecture_family#Advanced_SIMD_(Neon)[Neon] allow us to very quickly inspect the full metadata word and look for the reduced value of _h_ among all the 15 buckets with just a handful of CPU instructions: non-matching buckets can be readily discarded, and those whose reduced hash value matches need be inspected via full comparison with the corresponding element. If the looked-for element is not present, the overflow byte is inspected:等 SIMD 技术，仅需少量 CPU 指令即可快速检查完整的元数据字，并在全部 15 个桶中寻找 _h_ 的缩减值：不匹配的桶可以迅速丢弃，而那些缩减哈希值匹配的桶则需要通过与对应元素的完整比较来进行检查。如果未找到目标元素，则检查溢出字节。
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- 0 if the corresponding bucket is empty. - 1 to encode a special empty bucket called a _sentinel_, which is used internally to stop iteration when the container has been fully traversed. - If the bucket is occupied, a _reduced hash value_ obtained from the hash value of the element.
- 0 if the corresponding bucket is empty. - 1 to encode a special empty bucket called a _sentinel_, which is used internally to stop iteration when the container has been fully traversed. - If the bucket is occupied, a _reduced hash value_ obtained from the hash value of the element.表示对应的桶为空。
- 1 用于编码一种特殊的空桶，称为 _哨位桶_，在容器被完全遍历时内部用于停止迭代。
- 如果桶被占用，则存储从元素哈希值中获得的 _缩减哈希值_。
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A metadata word is divided into 15 _h_~_i_~ bytes (one for each associated bucket), and an _overflow byte_ (_ofw_ in the diagram). The value of _h_~_i_~ is:
A metadata word is divided into一个元数据字被划分为 15 个 _h_~_i_~ bytes (one for each associated bucket), and an _overflow byte_ (_ofw_ in the diagram). The value of _h_~_i_~ is:字节（每个字节对应一个关联的桶），以及一个 _溢出字节_（图中标记为 _ofw_）。_h_~_i_~ 的值计算方式如下：
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image::foa-metadata.png[align=center]
image::foa-metadata.png[align=center]
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