C++ 中如何使用线程局部存储？它的原理是什么？

#include <iostream>
#include <thread>

// 全局 thread_local 变量
thread_local int global_tls = 0;

void threadFunction() {
    // 每个线程都有自己的 global_tls 副本
    ++global_tls;
    std::cout << "Thread ID: " << std::this_thread::get_id() 
              << ", global_tls: " << global_tls << std::endl;
}

int main() {
    std::thread t1(threadFunction);
    std::thread t2(threadFunction);

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

    return 0;
}

#include <iostream>
#include <thread>

void threadFunction() {
    // 函数作用域中的 thread_local 变量
    thread_local int local_tls = 0;

    // 每个线程都有自己的 local_tls 副本
    ++local_tls;
    std::cout << "Thread ID: " << std::this_thread::get_id() 
              << ", local_tls: " << local_tls << std::endl;
}

int main() {
    std::thread t1(threadFunction);
    std::thread t2(threadFunction);

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

    return 0;
}