Порядок памяти с несколькими хранилищами ⇐ C++

[Гость]

Рассмотрим пример ниже. Предположим, что

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barrier

is initialized to 0.
There is one producer thread and two consumer threads that constantly check

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barrier

. If the barrier is set, they decrease

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runcnt

. The producer thread waits for

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runcnt

to reach 0. I am confused about the order of multiple store operations inside the producer.
If the order is like it is written, I think the code would run as expected. But if the

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barrier

store is reordered before

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runcnt

store, it seems the assert check would fail.
Am I missing anything? Is there a way to fix this?

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extern atomic barrier[2];
atomic_int runcnt{0};

void producer() {
runcnt.store(2, memory_order_relaxed);
barrier[0].store(1, memory_order_relaxed);
barrier[1].store(1, memory_order_relaxed);

while (runcnt.load(memory_order_relaxed)) {
cpu_pause();
}
}

void consumer(unsigned index) {
while (true) {
if (barrier[index].exchange(false, memory_order_relaxed)) {
int prev = runcnt.fetch_sub(1, memory_order_relaxed);
assert(prev > 0);
}
}
}

Источник: https://stackoverflow.com/questions/781 ... ple-stores