#include <stdio.h>
#include <string>
#include <atomic>
#include <thread>
#include <chrono>

using namespace std;

int tag = 0;
void func1()
{
    std::this_thread::sleep_for(chrono::milliseconds(100));
    tag = 1;
    //std::atomic_thread_fence(std::memory_order_relaxed);
}

void func2()
{
    while(tag == 0);
        //std::atomic_thread_fence(std::memory_order_relaxed);
}
int main()
{
    thread t1(func1);
    thread t2(func2);

    t1.join();
    printf(" t1 joined........\n");
    t2.join();

    printf(" finished........\n");

    return 0;
}

g++ a.cpp -O2 -std=c++11 -pthread  && ./a.out

程序挂住了

不开-O2不会挂住,加上volatile不会挂住,加上fence也不会挂住
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