Question

Implement the C code that would generate the following sequence diagram for process creation. Your code should output the pid of each process (print the return value from getpid once in each process) as it is created. Make sure you keep track of what process you're in at any given time, and that your calls to fork are in the correct spot. (Also, ensure that you are checking if each call to fork succeeded or not and printing an appropriate error message.)

Process 2 Process 3 Process1 fork fork) return

Answer 1

Program:

#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

void main()
{
   pid_t pid;
  
   if( (pid = fork()) == -1 )
   {
       printf("\n fork failed \n");
       exit(1);
   }
  
   else if( pid == 0 )
   {
       printf("\nProcess 1, pid : %d\n",getpid());
      
       if( (pid = fork()) == -1 )
       {
           printf("\n fork failed \n");
           exit(1);
       }
      
       else if( pid == 0 )
       {
           printf("\nProcess 2, pid : %d\n",getpid());
          
           if( (pid = fork()) == -1 )
           {
               printf("\n fork failed \n");
               exit(1);
           }
      
           else if( pid == 0 )
           {
               printf("\nProcess 3, pid : %d\n\n",getpid());
           }
      
           else
           {
               wait(NULL);
           }
      
       }
      
       else
       {
           wait(NULL);
       }
   }
  
   else
   {
       wait(NULL);
   }
}

Execution and Output:

gcc o processtree processtree.c $./processtree Process 1, pid :4826 Process 3, pid :4828