(Google interview question) There are four threads 1, 2, 3, and 4. The function of thread 1 is to output 1, the function of thread 2 is to output 2, and so on… There are now four files ABCD. Initially they are empty.

Now we want the four files to be in the following format:

A：1 2 3 4 1 2….

B：2 3 4 1 2 3….

C：3 4 1 2 3 4….

D：4 1 2 3 4 1….

Please design a program.

The following is an example of A. For B, C, and D, you only need to modify the initialization value of the global variable n:

 1 #include 
  2 #include 
  3 #include 
  4 using namespace std;
 5
  6 pthread_mutex_t myloack=PTHREAD_MUTEX_INITIALIZER;
  7 pthread_cond_t mycOnd=PTHREAD_COND_INITIALIZER;
  8 int n=0;
  9 void *ThreadFunc(void *arg)
 10 {
 11 int num=(int )arg;
 12 for (int i = 0; i <10  ; ++i)
 13  {
 14 pthread_mutex_lock(&myloack);
 15 while (n!=num)
 16 pthread_cond_wait(&mycond,&myloack);
 17
 18 if (num==0)
 19 cout<<"1";
 20 else if(num==1)
 21 cout<<"2";
 22 else if(num==2)
 23 cout<<"3";
 24 else
 25 cout<<"4"<<endl;
 26 n=(n+1)%4;
 27 pthread_mutex_unlock(&myloack);
 28 pthread_cond_broadcast(&mycond);
 29  }
 30 return (void *)0;
 31 }
 32
 33 int main(int argc, char const *argv[  ])
 34 {
 35
 36 pthread_t id[4];
 37 for (int i = 0; i <4  ; ++i)
 38  {
 39 int err=pthread_create(&id[i],NULL,ThreadFunc,(void *)i);
 40 if (err!=0)
 41  {
 42 cout<<"create err:"<<endl;
 43 exit(-1);
 44  }
 45
 46  }
 47
 48 for (int i = 0; i <4; ++i)
 49  {
 50 int ret=pthread_join(id[i],NULL);
 51 if (ret!=0)
 52  {
 53 cout<<"join err:"<<endl;
 54 exit(-1);
 55  }
 56  }
 57 return 0;
 58 }