C++多线程基础学习笔记（六）

condition_variable、wait、notifiy_one、notify_all的使用方式

condition_variable:条件变量

wait：等待被唤醒

notify_one：随机唤醒一个线程

notify_all:唤醒所有线程

下列代码是三个线程轮流打印数字

 #include <iostream>
 #include <thread>
 #include <mutex>
 using namespace std;

 class print
 {
 private:
     mutex mymutex;   //互斥锁
     condition_variable my_cond;  //条件变量
     int num;
     int flag;
     int count;
 public:
     print() {
         num = ;
         flag = ;
         count = ;
     }
     void print1() {
         while (count < ) {
             unique_lock<mutex> myunique(mymutex);
             if (flag != ) {
                 my_cond.wait(myunique);   //等待被notify_one或者notify_all唤醒
             }
             else {
                 flag = ;
                 cout << "thread_1:" << num++ << endl;
                 count++;
                 my_cond.notify_all();   //唤醒所有被锁的线程
             }
         }
     }
     void print2() {
         while (count < ) {
             unique_lock<mutex> myunique(mymutex);
             if (flag != ) {
                 my_cond.wait(myunique);
             }
             else {
                 cout << "thread_2:" << num++ << endl;
                 flag = ;
                 count++;
                 my_cond.notify_all();
             }
         }
     }
     void print3() {
         while (count < ) {
             unique_lock<mutex> myunique(mymutex);
             if (flag != ) {
                 my_cond.wait(myunique);
             }
             else {
                 flag = ;
                 cout << "thread_3:" << num++ << endl;
                 count++;
                 my_cond.notify_all();
             }
         }
     }
 };
 int main()
 {
     print p;
     thread thread_1(&print::print1, &p);
     thread thread_2(&print::print2, &p);
     thread thread_3(&print::print3, &p);
     thread_1.join();
     thread_2.join();
     thread_3.join();
     system("pause");
     return ;
 }