+在c ++中的运算符的线程安全性 [英] Thread safety of += operator in c++

问题描述

是否是c ++线程安全的 + = 运算符？

Is the += operator in c++ thread-safe?

可以想象一种情况，它不是（Pseudocode）：

It is possible to imagine a situation where it is not (Pseudocode):

int a = 5;

void thread1 () {
   a += 5;
}

void thread2 () {
   a += 5;
}

void main () {
    start_thread1 ();
    start_thread2 ();
    //Prints 15 always, but i think 10 is not impossible.
    printf ("%d\n", a);
}

很明显，当+ =重载时，我必须使用Mutexes，

It is obvious, that i must use Mutexes when += is overloaded, but do i have to set a mutex when working with simple types?

推荐答案

这是不是

为了获得同步行为而不使用阻塞（mutexes），你可以使用C ++ 11包装器 std :: atomic 。

To get synchronized behaviour without using blocking (mutexes) you could e.g. use the C++11 wrapper std::atomic.

std::atomic<int> a{5};

void work() {
    a += 5; // Performed atomically.
}

int main() {
    std::thread t1{work};
    std::thread t2{work};

    t1.join();
    t2.join();

    std::cout << a << std::endl; // Will always output 15.
}

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