代码

#include<iostream>
#include<thread>
#include<mutex>
#include<condition_variable>
using namespace std;
mutex mtx;
condition_variable cv;
int flag=0;
void A(){
    unique_lock<mutex>lk(mtx);
    int count=0;
    while(count<10){
        while(flag!=0) cv.wait(lk);
        cout<<"thread1 : a"<<endl;
        count++;
        this_thread::sleep_for(chrono::milliseconds(500));
        flag=1;
        cv.notify_all();
        
    }
    cout<<"thread 1 finish"<<endl;

}
void B(){
    unique_lock<mutex>lk(mtx);
    int count=0;
    while(count<10){
        while(flag!=1) cv.wait(lk);
        cout<<"thread 2 : b"<<endl;
        this_thread::sleep_for(chrono::milliseconds(500));
        flag=2;
        cv.notify_all();
        count++;
    }
    cout<<"thread 2 finished"<<endl;

}
void C(){
    unique_lock<mutex>lk(mtx);
    int count=0;
    while(count<10){
        while(flag!=2) cv.wait(lk);
        cout<<"thread 3 : c"<<endl;
        this_thread::sleep_for(chrono::milliseconds(500));
        flag=0;
        cv.notify_all();
        count++;
    }
    cout<<"thread 3 finished"<<endl;

}
int main(){
    thread t1(A);
    thread t2(B);
    thread t3(C);
    t1.join();
    t2.join();
    t3.join();
    return 0;

}

结果