C++并发实战：面试题1：一道多线程笔试题

#include<iostream>
#include<thread>
#include<mutex>
#include<condition_variable>
using namespace std;
mutex m;
condition_variable cond;
int flag=10;
void fun(int num){
for(int i=0;i<50;i++){
unique_lock<mutex> lk(m);//A unique lock is an object that manages a mutex object with unique ownership in both states: locked and unlocked.
while(flag!=num)
cond.wait(lk);//在调用wait时会执行lk.unlock()
for(int j=0;j<num;j++)
cout<<j<<" ";
cout<<endl;
flag=(num==10)?100:10;
cond.notify_one();//被阻塞的线程唤醒后lk.lock()恢复在调用wait前的状态
}
}
int main(){
thread child(fun,10);
fun(100);
child.join();
return 0;
}