Question

Modify the template program below and include the following additional functionalities:

- Instead of 3 children processes, create 6 children processes.

- 6 children processes are connected to the parent process via 6 pipes, one for each pair, child1-parent, child2-parent, child3-parent, ....

- Child keeps writing to the pipe with 1 second apart between consecutive writes (as in child() in p. 167).

- Keyboard inputs need to be monitored as in the original code.

- Parent keeps reading from the 6 pipes and keyboard whenever any of them has data ready for reading.

- You have to use the “select” system call with a non-blocking feature as was done in the template program.

#include
#include

#define MSGSIZE 6

char *msg1 = "hello";
char *msg2 = "bye!!";

void parent(int [][]);
int child(int []);

main()
{
int pip[3][2];
int i;

for(i = 0; i < 3; i++)
{
if(pipe(pip[i]) == -1)
fatal("pipe call");

switch(fork()){
case -1:
fatal("fork call");
case 0:
child(pip[i]);
}
}

parent (pip);

exit(0);
}

void parent(int p[3][2])
{
char buf[MSGSIZE], ch;
fd_set set, master;
int i ;

for(i = 0; i < 3; i++)
close(p[i][1]);

FD_ZERO(&master);
FD_SET(0, &master);

for(i = 0; i < 3; i++)
FD_SET(p[i][0], &master);

while(set = master, select(p[2][0]+1, &set, NULL, NULL, NULL) > 0)
{
if(FD_ISSET(0, &set))
{
printf("From standard input...");
read(0, &ch, 1);
printf("%c\n", ch);
}

for(i = 0; i < 3; i++)
{
if(FD_ISSET(p[i][0], buf, &set))
{
if(read(p[i][0], buf, MSGSIZE)>0)
{
printf("Message from child%d\n", i);
printf("MSG=%s\n", buf);
}
}
}

if(waitpid(-1, NULL, WNOHANG) == -1)
return;
}
}

int child(int p[2])
{
int count;

close(p[0]);

for(count = 0; count < 2; count++)
{
write(p[1], msg1, MSGSIZE);
sleep(getpid() % 4);
}

write(p[1], msg2, MSGSIZE);
exit(0);
}

Answer 1

// Chegg1_C++.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#define MSGSIZE 6

char *msg1 = "hello";
char *msg2 = "bye!!";

void parent(int [][]);
int child(int []);

main()
{
   int pip[6][2]; // 6 children processes are connected to the parent process via 6 pipes
   int i;

   for(i = 0; i < 6; i++) //"Instead of 3 children processes, create 6 children processes."
   {
       if(pipe(pip[i]) == -1)
       fatal("pipe call");

       switch(fork())
       {
       case -1:
       fatal("fork call");
       case 0:
       child(pip[i]);
       }
   }

parent (pip);
exit(0);
}

void parent(int p[6][2])
{
   char buf[MSGSIZE], ch;
   fd_set set, master;
   int i ;

   for(i = 0; i < 6; i++)
   close(p[i][1]);

   FD_ZERO(&master);
   FD_SET(0, &master);

   for(i = 0; i < 6; i++)
   FD_SET(p[i][0], &master);

   while(set = master, select(p[2][0]+1, &set, NULL, NULL, NULL) > 0)
   {
       if(FD_ISSET(0, &set))
       {
           printf("From standard input...");
           read(0, &ch, 1);
           printf("%c\n", ch);
       }

       for(i = 0; i < 6; i++)
       {
           if(FD_ISSET(p[i][0], buf, &set))
               {
                   if(read(p[i][0], buf, MSGSIZE)>0)
                       {
                       printf("Message from child%d\n", i);
                       printf("MSG=%s\n", buf);
                       }
               }
       }

       if(waitpid(-1, NULL, WNOHANG) == -1)
       return;
   }
}

int child(int p[2])
{
   int count;

   close(p[0]);

   for(count = 0; count < 2; count++)
   {
       write(p[1], msg1, MSGSIZE); //Child keeps writing to the pipe with 1 second apart between consecutive writes
       sleep(1);
   }

   write(p[1], msg2, MSGSIZE);
   exit(0);
}