#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(zhí)行函數(shù)
 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(diào)用后，會(huì)先釋放鎖，之后進(jìn)入等待狀態(tài)；當(dāng)其它進(jìn)程調(diào)用通知激活后，會(huì)再次加鎖
 }
 std::cout << "func thread exit" << std::endl;
}
int main() {
 int     n = 100;
 std::thread t1(ThreadFunc, n);    // 創(chuàng)建t1線程（func thread），t1會(huì)執(zhí)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(jié)束
 std::cout << "g_i = " << g_i << std::endl;
}

plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by func thread 139921006847744
plus g_i by func thread 139921006847744
plus g_i by func thread 139921006847744
plus g_i by func thread 139921006847744
plus g_i by func thread 139921006847744
wait for exit               // func thread等待main thread發(fā)來(lái)的退出信號(hào)
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
plus g_i by main thread 139921025066816
func thread exit
g_i = 200     // 鎖機(jī)制保證了g_i的正確

std::this_thread::get_id()
g_i

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