FORK

PROCESS - it is basically a program under execution

fork is used to create a child processs :) p1 / \
c1 c2 fork always return the process id.

Fork can return either a zero value or a positive value or a negative value

-ve value

• if it return negative value the it means their is unsucessful excution of fork i.e. no child process is created

  Zero value

• it means the child process is being created

  +ve value

• it means the child process is being created and it returns the process id of the procress

//give the output of the code

main(){    fork()    printf("hello");}

// this will print hello for two times one for parent and one for the child

main(){    fork()    fork()    printf("hello");}

// this will print hello for 4 times

• to find how many times it would be printed

  2^n

• to find the total number of child process

  2^n - 1

  How to implement fork system call ?

  when ever the fork is called it will create a clone of it what ever is written downward of it.

  // for standard input and output#include <stdio.h>// for the system calls#include <unistd.h>
  int main(){    fork();    printf("today is friday");}
  

  output
   gauravtewari@Gauravs-MacBook-Air  ~/Desktop/os/fork  ./a.out                                                                                                                         ✔  534  21:36:05today is fridaytoday is friday%                                                                                                                                                                              

  main system call will print first after that the child call call would print it output

  meow meow it works today is friday today is 22 oct today is friday today is 22 oct today is 22 oct today is 22 oct 

Parent Process Computes the SUM OF EVEN and Child Process Computes the sum of ODD NUMBERS using fork

• this program does not work check another the another program

#include<stdio.h>//for using the fork #include<unistd.h>//for exit function#include<stdlib.h>//to call states of particular processs#include<sys/types.h>#include<sys/wait.h>

//this limits and interger array#define max 20  int main(){    //  to store the process id    //this will store the process id      int pid;      int a[max],n,sum=0,i,status;     scanf("%d",&n);     printf("enter the values in an array\n");     for(i=0;i<n;i++){         scanf("%d",&a[i]);         pid = fork();         //this will put the parent program on hold untill the child process is completed         wait(&status);        // pid zero means the child process has been created         if(pid == 0){          for(i=0;i<n;i++){              if(a[i]%2 == 0){                  sum += a[i];              }          }                  printf("sum of even places %d\n", sum);                        }          exit(0);         }else{              for(i=0;i<n;i++){              if(a[i]%2 != 0){                  sum += a[i];              }             printf("sum of even places %d\n", sum);
          }          exit(0);         }     }     return 0; }

// for standard input and output#include <stdio.h> // for the system calls #include <unistd.h> #define max 20
 int main(){     int a[max],n,i ,sumEven = 0, sumOdd = 0 , m;     printf("enter the size of array\n");     scanf("%d",&n);     printf("enter the array elements\n");     for(i=0;i<n;i++){         scanf("%d",&a[i]);     }        m = fork();     if(m>0){         for(i=0;i<n;i++){                          if(a[i]%2 == 0){             sumEven += a[i];             }         }         printf("parent process \n");         printf("sum of Even %d \n",sumEven);     }else{         for(i=0;i<n;i++){             if(a[i]%2 != 0){             sumOdd +=a[i];             }
         }         printf("child process \n");         printf(" sum of odd %d \n" , sumOdd);
     }   return 0; }