打印要求:
三个打印线程顺序进行。
线程要求如下:
线程A:打印A
线程B:打印B
线程C:打印C
打印结果:
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
法一:需要锁和共享变量
#include <iostream>
#include <thread>
#include <mutex>using std::cout;
using std::endl;
using std::thread;
using std::mutex;
using std::condition_variable;
using std::unique_lock;enum CVFLAG
{INIT,A_DONE,B_DONE,C_DONE
};mutex mtx;
condition_variable cv;
CVFLAG flag = INIT;void printA()
{unique_lock<mutex> lock(mtx);cout << "A" << endl;flag = A_DONE;cv.notify_all();
}void printB()
{unique_lock<mutex> lock(mtx);cv.wait(lock, [] { return flag == 1; });cout << "B" << endl;flag = B_DONE;cv.notify_all();
}void printC()
{unique_lock<mutex> lock(mtx);cv.wait(lock, [] { return flag == 2; });cout << "C" << endl;flag = C_DONE;cv.notify_all();
}int main()
{int i = 0;while (i < 5){thread tA(printA);thread tB(printB);thread tC(printC);tA.join();tB.join();tC.join();++i;}return 0;
}
法二:简单粗暴,调整join的顺序
#include <iostream>
#include <thread>
#include <mutex>using std::cout;
using std::endl;
using std::thread;void printA()
{cout << "A" << endl;
}void printB()
{cout << "B" << endl;
}void printC()
{cout << "C" << endl;
}int main()
{int i = 0;while (i < 5){thread tA(printA);tA.join();thread tB(printB);tB.join();thread tC(printC);tC.join();++i;}return 0;
}