有关volatile的例子。一般用atomic来保存多线程的同步性，而非volatile。

volatile.cpp

#include <iostream>
#include <thread>

// 这个链接说这样写会产生问题，但是在mac上测试并没有问题
// 链接：https://liam.page/2018/01/18/volatile-in-C-and-Cpp/
namespace sanjay1 {
    bool flag = false;
    using Type = int;

    void test_volatile_demo() {
        flag = false;
        Type* value = new Type(1);
        auto func_thread2 = [](Type* value)->void {
            // do something
            std::cout << "func_thread2 begin" << std::endl;
            *value = 22;
            flag = true;
        };

        std::thread t(func_thread2, value);
        while (true) {
            if(flag == true) {
                std::cout << "applay value: " << *value << std::endl;
                break;
            }
        }
        t.join();
        if(value != nullptr) {
            delete value;
        }
    }
}

// 更好的写法
#include <atomic>
namespace sanjay2{
    std::atomic<bool> flag = false;
    using Type = int;

    void test_volatile_demo() {
        flag = false;
        Type* value = new Type(1);
        auto func_thread2 = [](Type* value)->void {
            // do something
            std::cout << "func_thread2 begin" << std::endl;
            *value = 22;
            flag = true;
        };

        std::thread t(func_thread2, value);
        while (true) {
            if(flag == true) {
                std::cout << "applay value: " << *value << std::endl;
                break;
            }
        }
        t.join();
        if(value != nullptr) {
            delete value;
        }
    }
}



int main() {
    for(size_t i = 0; i < 1000000000; ++i) {
        sanjay2::test_volatile_demo();
    }
    return 0;
}