多个读取器可以通过获取/释放顺序与相同的写入器同步吗？

Question

After reading "Concurrency in action" I could not find an answer to one question - are there guarantees in the standard for reading side effects when we have one store(release) and many loads(acquire) on one atomic variable? Suppose we have:

int i{};
atomic<bool> b{};

void writer(){
 i=42;
 b.store(true,memory_order_release);
}

void reader(){
 while(!b.load(memory_order_acquire))
    this_thread::yield();
 assert(i==42);
}
//---------------------
thread t1{writer},t2{reader},t3{reader};

If we had only one reader, all ok, but can we have failed assertion in t2 or t3 thread?

Answer 1

This is a text-book example of a happens-before relationship between the store to i in writer and the load from i in both reader threads.

That multiple readers are involved does not matter. The store to b synchronizes with all readers that observe the updated value (which will eventually happen thanks to the loop).

I think the quote you're looking for is:

An atomic operation A that performs a release operation on an atomic object M synchronizes with an atomic operation B that performs an acquire operation on M and takes its value from any side effect in the release sequence headed by A.

It does not say that this is limited to a single load operation