CODEWITHSUNDEEP
c++c++11concurrencyatomic
york.beta
york.beta

Reputation: 1827

Is it correct to use memory_order_relaxed at this code?

Is it correct to use std::memory_order_relaxed at the following code?

#include <atomic>
#include <array>
#include <iostream>
#include <thread>

using namespace std;

int main() {
    std::atomic<int> counter(0);

    constexpr size_t thread_count = 10;
    std::array<std::thread, thread_count> threads;
    for (auto& th : threads) {
        th = std::thread([&counter]() {
            for (int j = 0; j < 100; ++j) {
/*1*/           counter.fetch_add(1, std::memory_order_relaxed);
            }
        });
    }

    for (auto& th : threads) th.join();

/*2*/ std::cout << counter.load(std::memory_order_relaxed) << std::endl;

    return 0;
}

I have a method call counter. It doesn't matter when the counter will be actually incremented (/*1*/), it's enough if it will be incremented some time. But when I call atomic::load (/*2*/), all counter changes that have been made should be visible.

Is it correct to use std::memory_order_relaxed in lines /*1*/ and /*2*/?

Upvotes: 3

Views: 648

Answers (1)

Kerrek SB
Kerrek SB

Reputation: 477040

Yes, that's fine. The thread joining provides the necessary synchronization point that ensures that the final load() sees the correct value.

Upvotes: 5

Related Questions