#include <iostream>#include <mutex>#include <thread>#include <condition_variable>std::mutex       g_mutex;   // 用到的全局鎖std::condition_variable g_cond;   // 用到的條件變量int g_i    = 0;bool g_running = true;void ThreadFunc(int n) {       // 線程執行函數 for (int i = 0; i < n; ++i) {  {   std::lock_guard<std::mutex> lock(g_mutex);   // 加鎖，離開{}作用域后鎖釋放   ++g_i;   std::cout << "plus g_i by func thread " << std::this_thread::get_id() << std::endl;  } } std::unique_lock<std::mutex> lock(g_mutex);    // 加鎖 while (g_running) {  std::cout << "wait for exit" << std::endl;  g_cond.wait(lock);                // wait調用后，會先釋放鎖，之后進入等待狀態；當其它進程調用通知激活后，會再次加鎖 } std::cout << "func thread exit" << std::endl;}int main() { int     n = 100; std::thread t1(ThreadFunc, n);    // 創建t1線程（func thread），t1會執行`ThreadFunc`中的指令 for (int i = 0; i < n; ++i) {  {   std::lock_guard<std::mutex> lock(g_mutex);   ++g_i;   std::cout << "plus g_i by main thread " << std::this_thread::get_id() << std::endl;  } } {  std::lock_guard<std::mutex> lock(g_mutex);  g_running = false;  g_cond.notify_one();   // 通知其它線程 } t1.join();     // 等待線程t1結束 std::cout << "g_i = " << g_i << std::endl;}

plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by func thread 139921006847744plus g_i by func thread 139921006847744plus g_i by func thread 139921006847744plus g_i by func thread 139921006847744plus g_i by func thread 139921006847744wait for exit               // func thread等待main thread發來的退出信號plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816plus g_i by main thread 139921025066816func thread exitg_i = 200     // 鎖機制保證了g_i的正確

std::this_thread::get_id()g_i

{ std::lock_guard<std::mutex> lock(g_mutex); ......}