N个孩子向父母发送消息

Question

我所做的是我创建了n个孩子，并且父母使用n个管道向他们发送了“开始”消息。每个孩子一个管道。现在我正在努力做的事情是将父母的数量发回给每个孩子。

这是我的代码至今：

int main() 
{ 
int n=5; 

int p[n-1][2]; 

int i; 
for(i=0;i<n;i++){ 
    if(pipe(p[i])>0){ 
     perror("pipe error"); 
     exit(1); 
    } 
} 

for(i=0;i<n;i++){ 
    pid_t pid=fork(); 
    if(pid<0){ 
     perror("fork error"); 
     exit(1); 
    } 
    if(pid==0){ 
     int j; 
     for(j=0;j<n;j++){ 
      close(p[j][1]); 
     } 
     for(j=0;j<i;j++){ 
      close(p[j][0]); 
     } 
     char msg[256]; 
     int h; 
     read(p[i][0],&h,sizeof(int)); 
     read(p[i][0],msg,h*sizeof(char)); 
     cout<<i<<"_"<<msg<<endl; 
     close(p[i][0]);//here I would like to send the number i to the parent 
     for(j=i+1;j<n;j++){ 
      close(p[j][0]); 
     } 
     exit(0); 
    } 
} 

char ms[256]; 
strcpy(ms,"start"); 
int ho=strlen(ms); 
for(i=0;i<n;i++){ 
    if(write(p[i][1],&ho,sizeof(int))==-1){ 
     perror("write error"); 
     exit(1); 
    } 
    if(write(p[i][1],ms,ho*sizeof(ms))==-1){ 
     perror("write error"); 
     exit(1); 
    } 
    close(p[i][1]); 
} 
for(int j=0;j<n;j++) 
    close(p[j][0]);//then read the number of each child and print it 
while(wait(NULL)>0){}; 
exit(0); 

}

这是输出：

0_start 
    2_start 
    1_start 
    4_start 
    3_start 

所以我成功发送的消息开始到各child.But我可以我们不知道父母如何接收孩子们发送的号码。

Answer 1

你可以做一个类似的过程但是在这里父节点有管道的读端和写端的子节点。扩展上面的例子只包含一个管道。每个孩子可以有多个管道。

int main() 
{ 
int n=5; 

int p[n-1][2]; 
int pw[2]; // pipe child writes into 

int i; 
for(i=0;i<n;i++){ 
    if(pipe(p[i])>0){ 
     perror("pipe error"); 
     exit(1); 
    } 
} 
    if(pipe(pw)>0){ 
     perror("pipe error"); 
     exit(1); 
    } 

for(i=0;i<n;i++){ 
    pid_t pid=fork(); 
    if(pid<0){ 
     perror("fork error"); 
     exit(1); 
    } 
    if(pid==0){ 
     int j; 
     for(j=0;j<n;j++){ 
      close(p[j][1]); 
     } 
     close(pw[0]);// close read end - child 
     for(j=0;j<n;j++){ 
      if (i!= j) close(p[j][0]); 
     } 
     char msg[256]; 
     int h; 
     read(p[i][0],&h,sizeof(int)); 
     read(p[i][0],msg,h*sizeof(char)); 
     cout<<i<<"_"<<msg<<endl; 
     close(p[i][0]);//here I would like to send the number i to the parent 
     write(pw[1],&i,sizeof(int)); // send i 
     close(pw[1]); 
     exit(0); 
    } 
} 

char ms[256]; 
strcpy(ms,"start"); 
int ho=strlen(ms); 
int value; 
for(i=0;i<n;i++){ 
    if(write(p[i][1],&ho,sizeof(int))==-1){ 
     perror("write error"); 
     exit(1); 
    } 
    if(write(p[i][1],ms,ho*sizeof(ms))==-1){ 
     perror("write error"); 
     exit(1); 
    } 
    close(p[i][1]); 
    close(pw[1]); //close write end 
    if(read(pw[0],&value,sizeof(int))==-1){ // read from child process 
     perror("write error"); 
     exit(1); 
    } 
    cout << " in main "<<value<<endl; // display number 
} 
for(int j=0;j<n;j++) 
    close(p[j][0]);//then read the number of each child and print it 
while(wait(NULL) > 0){;} 
exit(0); 
}