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book: revise release acquire semantics

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Fixes #174
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Changkun Ou
2021-08-11 13:10:34 +02:00
parent b0f6f30988
commit 93ce6490a6
2 changed files with 5 additions and 4 deletions
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book/en-us/07-thread.md
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@@ -464,8 +464,9 @@ To achieve the ultimate performance and achieve consistency of various strength
3. Release/Acquire model: Under this model, we can further tighten the order of atomic operations between different threads, specifying the timing between releasing `std::memory_order_release` and getting `std::memory_order_acquire`. **All** write operations before the release operation is visible to any other thread, i.e., happens before.
As you can see, `std::memory_order_release` ensures that the write behavior after it does not occur before the release operation, which is a forward barrier, and`std::memory_order_acquire` ensures that its previous write behavior does not occur after this acquisition operation, there is a backward barrier. For the `std::memory_order_acq_rel` option, combines the characteristics of the two and uniquely determines a memory barrier, so that the current thread's reading and writing of memory will not be rearranged before and after this operation.
As you can see, `std::memory_order_release` ensures that a write before a release does not occur after the release operation, which is a **backward barrier**, and `std::memory_order_acquire` ensures that a subsequent read or write after a acquire does not occur before the acquire operation, which is a **forward barrier**.
For the `std::memory_order_acq_rel` option, combines the characteristics of the two barriers and determines a unique memory barrier, such that reads and writes of the current thread will not be rearranged across the barrier.
Let's check an example:
```cpp