[C++知识库]按序打印ABC（c++实现）

#include <iostream>
#include <thread>
#include <mutex>
#include <condition_variable>

using namespace std;

#define PRINT_TIME 30                                                                                                                                

mutex mtx;
condition_variable cv; 
int flag = 0;

void printA()
{
    unique_lock<mutex> lk(mtx);
    for(int i = 0; i < PRINT_TIME; ++i){
        // condition_variable 对象通常使用 std::unique_lock 来等待
        while(flag != 0) cv.wait(lk);
        cout << "thread 1: a" << endl;
        // 其余线程跳出阻塞条件
        flag = 1;
        cv.notify_all();
    }
    cout << "thread 1 finish" << endl;
}

void printB()
{
    unique_lock<mutex> lk(mtx);
    for(int i = 0; i < PRINT_TIME; ++i){
        while(flag != 1) cv.wait(lk);
        cout << "thread 2: b" << endl;
        flag = 2;
        cv.notify_all();
    }
    cout << "thread 2 finish" << endl;
}

void printC()
{
    unique_lock<mutex> lk(mtx);
        for(int i = 0; i < PRINT_TIME; ++i){
        while(flag != 2) cv.wait(lk);
        cout << "thread 3: c" << endl;
        flag = 0;
        cv.notify_all();
    }
    cout << "thread 3 finish" << endl;
}

int main()
{
    thread th1(printB);
    thread th2(printA);
    thread th3(printC);

    th1.join();
    th2.join();
    th3.join();

    cout << "main finish" << endl;

	return 0;
}

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