【C++】thread_local变量

在C++多线程环境下，全局变量、局部变量、静态变量和thread_local变量的区别如下：

	全局变量	局部变量	静态变量	thread_local变量
存储期	程序运行期间	函数调用期间	程序运行期间	线程运行期间
线程安全	×	√	×	√

示例程序

#include <iostream>
#include <thread>

int g = 0;

void global_test() {
    std::cout << &g << '\n';
    for (int i = 0; i < 10000; ++i) ++g;
    std::cout << g << '\n';
}

void local_test() {
    int n = 0;
    std::cout << &n << '\n';
    for (int i = 0; i < 10000; ++i) ++n;
    std::cout << n << '\n';
}

void static_test() {
    static int n = 0;
    std::cout << &n << '\n';
    for (int i = 0; i < 10000; ++i) ++n;
    std::cout << n << '\n';
}

void thread_local_test() {
    thread_local int n = 0;
    std::cout << &n << '\n';
    for (int i = 0; i < 10000; ++i) ++n;
    std::cout << n << '\n';
}

int main() {
    for (auto f : {global_test, local_test, static_test, thread_local_test}) {
        std::thread t1(f), t2(f);
        t1.join();
        t2.join();
    }
    return 0;
}

可能的输出结果：

0x10b7fb01c
0x10b7fb01c
10148
19117
0x7000078cdf2c
0x700007950f2c
10000
10000
0x108d0001c
0x108d0001c
15854
15936
0x600001008000
0x600001004050
10000
10000

参考

• Storage class specifiers - cppreference