stdatomic

问题 The paper N4455 No Sane Compiler Would Optimize Atomics talks about various optimizations compilers can apply to atomics. Under the section Optimization Around Atomics, for the seqlock example, it mentions a transformation implemented in LLVM, where a fetch_add(0, std::memory_order_release) is turned into a mfence followed by a plain load, rather than the usual lock add or xadd . The idea is that this avoids taking exclusive access of the cacheline, and is relatively cheaper. The mfence is

问题 I was looking through 'Atomic operations library' and came across a new c++20 feature of atomic 'wait' and 'notify_ ' methods. I am curious on what the differences are in regards to std::condition_variable's 'wait' and 'notify_ ' methods. 回答1: std:atomic wait , notify_all and notify_one methods are similar to methods of conditional variables. They allow the implementation of the logic that previously required conditional variable by using much more efficient and lightweight atomic variables.

问题 I was looking through 'Atomic operations library' and came across a new c++20 feature of atomic 'wait' and 'notify_ ' methods. I am curious on what the differences are in regards to std::condition_variable's 'wait' and 'notify_ ' methods. 回答1: std:atomic wait , notify_all and notify_one methods are similar to methods of conditional variables. They allow the implementation of the logic that previously required conditional variable by using much more efficient and lightweight atomic variables.

问题 I was looking through 'Atomic operations library' and came across a new c++20 feature of atomic 'wait' and 'notify_ ' methods. I am curious on what the differences are in regards to std::condition_variable's 'wait' and 'notify_ ' methods. 回答1: std:atomic wait , notify_all and notify_one methods are similar to methods of conditional variables. They allow the implementation of the logic that previously required conditional variable by using much more efficient and lightweight atomic variables.

问题 According to this https://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html, a released store is implemented as MOV (into memory) on x86 (including x86-64). According to his http://en.cppreference.com/w/cpp/atomic/memory_order memory_order_release : A store operation with this memory order performs the release operation: no memory accesses in the current thread can be reordered after this store. This ensures that all writes in the current thread are visible in other threads that acquire or the

问题 According to this https://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html, a released store is implemented as MOV (into memory) on x86 (including x86-64). According to his http://en.cppreference.com/w/cpp/atomic/memory_order memory_order_release : A store operation with this memory order performs the release operation: no memory accesses in the current thread can be reordered after this store. This ensures that all writes in the current thread are visible in other threads that acquire or the

问题 According to this https://www.cl.cam.ac.uk/~pes20/cpp/cpp0xmappings.html, a released store is implemented as MOV (into memory) on x86 (including x86-64). According to his http://en.cppreference.com/w/cpp/atomic/memory_order memory_order_release : A store operation with this memory order performs the release operation: no memory accesses in the current thread can be reordered after this store. This ensures that all writes in the current thread are visible in other threads that acquire or the

问题 As I see from a test-case: https://godbolt.org/z/K477q1 The generated assembly load/store atomic relaxed is the same as the normal variable: ldr and str So, is there any difference between relaxed atomic and normal variable? 回答1: The difference is that a normal load/store is not guaranteed to be tear-free, whereas a relaxed atomic read/write is. Also, the atomic guarantees that the compiler doesn't rearrange or optimise-out memory accesses in a similar fashion to what volatile guarantees.

来源： https://stackoverflow.com/questions/58804138/memory-model-how-load-acquire-semantic-actually-works

来源： https://stackoverflow.com/questions/59099401/why-does-default-constructor-of-stdatomic-not-default-initialize-the-underlyin