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 = 1;
        flag = 1;
        count = 0;
    }
    void print1() {
        while (count < 8) {
            unique_lock<mutex> myunique(mymutex);
            if (flag != 1) {
                my_cond.wait(myunique);   //等待被notify_one或者notify_all唤醒
            }
            else {
                flag = 2;
                cout << "thread_1:" << num++ << endl;
                count++;
                my_cond.notify_all();   //唤醒所有被锁的线程
            }
        }
    }
    void print2() {
        while (count < 8) {
            unique_lock<mutex> myunique(mymutex);
            if (flag != 2) {
                my_cond.wait(myunique);
            }
            else {
                cout << "thread_2:" << num++ << endl;
                flag = 3;
                count++;
                my_cond.notify_all();
            }
        }
    }
    void print3() {
        while (count < 8) {
            unique_lock<mutex> myunique(mymutex);
            if (flag != 3) {
                my_cond.wait(myunique);
            }
            else {
                flag = 1;
                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 0;
}