With the relaxed semantic, we have no synchronisations and ordering constraints on atomic operations.
But we can do better and further improve the acquire-release semantic of the last post. Why should x be an atomic? There is no reason. That was my first, but incorrect assumption. See why?
With the acquire-releae semantic, we break the sequential consistency. In the acquire-release semantic the synchronization takes place between atomic operations on the same atomic and not between threads.
With atomic data types, you can tailor your program to your needs and therefore optimize it. But now we are in the domain of the multithreading experts.
CppMem is an interactive tool for exploring the behaviour of small code snippets of the C++ memory model. It should, no it has to be in the toolbox of each programmer, who deals seriously with the memory model.
The relaxed semantic is the end of the Scala. The relaxed semantic is the weakest of all memory models and guarantees only, that the operations on atomic variables are atomic.
Acquire and release fences guarantees similar synchronisation and ordering constraints as atomics with acquire-release semantic. Similar, because the differences are in the details.
The key idea of a std::atomic_thread_fence is, to establish synchronisation and ordering constraints between threads without an atomic operation.
A release operation synchronizes-with an acquire operation on the same atomic variable. So we can easily synchronise threads, if ... . Today's post is about the if.
std::memory_order_consume is the most legendary of the six memory models. That's for two reasons. On one hand, std::memory_order_consume is extremely hard to get. On the other hand - that may change in the future - no compiler supports it.
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