循环中的std::thread导致不正确的结果

#include <iostream>
#include <thread>
#include <mutex>

std::mutex mtx;  // 定义互斥锁

void foo(int& sharedData) {
    for (int i = 0; i < 1000; ++i) {
        std::lock_guard<std::mutex> lock(mtx);  // 加锁
        sharedData++;
    }
}

int main() {
    int sharedData = 0;
    std::thread t1(foo, std::ref(sharedData));  // 启动线程1
    std::thread t2(foo, std::ref(sharedData));  // 启动线程2
    t1.join();
    t2.join();
    std::cout << "sharedData: " << sharedData << std::endl;
    return 0;
}

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

std::atomic<int> sharedData(0);  // 定义原子变量

void foo() {
    for (int i = 0; i < 1000; ++i) {
        sharedData++;
    }
}

int main() {
    std::thread t1(foo);  // 启动线程1
    std::thread t2(foo);  // 启动线程2
    t1.join();
    t2.join();
    std::cout << "sharedData: " << sharedData << std::endl;
    return 0;
}

#include <iostream>
#include <thread>

thread_local int sharedData = 0;  // 定义线程局部变量

void foo() {
    for (int i = 0; i < 1000; ++i) {
        sharedData++;
    }
}

int main() {
    std::thread t1(foo);  // 启动线程1
    std::thread t2(foo);  // 启动线程2
    t1.join();
    t2.join();
    std::cout << "sharedData: " << sharedData << std::endl;
    return 0;
}