Program hanged or stop execution randomly using fork() and signal

Question

I have written a program where I have created a child process. Both the parent process and child process do calculation in two parts- parent_part1 , parent_part2 and child_part1, child_part2.

My aim is to run the (parent_part1,child_part1,parent_part2 ,child_part2) sequence for let us say 5 times. For this purpose I have used while(var_child++<10) and while(var_par++<10) and successfully achieved it.

Now, I will define ONE SUCCESSFUL calculation is execution of (parent_part1,child_part1,parent_part2 ,child_part2) sequence for 5 times and display the final correct value.

I want to find such 100 SUCCESSFUL calculation and for the same purpose I have used OUTER loop (i.e., while(t1++<100) ), but I am not getting the SUCCESSFUL calculation for 100 times , sometimes I got 40 SUCCESSFUL result, and hanged after parent_part1 or parent_part2 or child_part1 or child_part2 etc. and some other times I got 20 or 95 SUCCESSFUL result, and hanged after parent_part1 or parent_part2 or child_part1 or child_part2 etc.

What is the reason and how to overcome this ? Thank you in advance . The program is as below.

#include<stdio.h>
#include<signal.h>
int flagp=0,flagc=0,var_child=0,var_par=0;

void write_child()  
{      

    if(flagc==0) 
    {
        /* do some computation here*/   
        printf("Child_part1 \n");       
        flagc=1;
    }

    else
    {
    /* do some computation here*/
    flagc=0;
    printf("Child_part2 \n");       
    }

}

void write_parent()
{

    if(flagp==0) 
    {
        /* do some computation here*/
        printf("Parent_part1 \n");      
        flagp=1; 
    }

    else
    {
        /* do some computation here*/
        printf("Parent_part2 \n");      
        flagp=0;
    }
}


int main(int ac, char **av)
{



        printf("Starting...\n");
        int t1=0;
        pid_t childpid = fork();    

        printf("childpid=%d,getppid()=%d \n",childpid,getppid());


while(t1++<100)
{

var_child=0;
    var_par=0;


    if ( childpid == 0 )
        { 
            // child process 
            printf("\n\nt1=%d ",t1);    
            while(var_child++<10)
            { 
            kill(getppid(), SIGCONT);  //sending singal to parent
            signal(SIGCONT, write_child);
            pause();
            }
        }



        else 
        {      
             //parent process   
            printf("\n\nt1=%d ",t1);
            while(var_par++<10)
            {               
            kill(childpid, SIGCONT); //sending singal to child
            signal(SIGCONT, write_parent);
            pause();
            }


        }  // end of else

}

return 0;
}

Here is my sample output : t1=1 Parent 1st part t1=1 Child 1st part Parent 2nd part Child 2nd part Parent 1st part Child 1st part Parent 2nd part Child 2nd part Parent 1st part Child 1st part Parent 2nd part Child 2nd part Parent 1st part Child 1st part Parent 2nd part Child 2nd part Parent 1st part Child 1st part Parent 2nd part Child 2nd part . . . t1=75 Parent 1st part Child 1st part Parent 2nd part Child 2nd part — bholanath, Oct 03 '13 at 15:43

score 0 · Answer 1 · answered Oct 03 '13 at 20:17

0

Are you sure this logic is correct?

  while(var_par++<10)

Apart from that, you are not catching the signal from the parent process. you are creating a lot of zombie processes when the child terminates and by killing the parent from child, you are creating orphans. Both will take system resources and might hit the upper limit on consecutive executions. Try catching the signal and see how it behaves.

answered Oct 03 '13 at 20:17

joe

1,136
9
17

Joe, Thanks for answering. As you mentioned "you are not catching the signal from the parent process" -but as per understanding I have used signal(SIGCONT, write_parent) in parent to cache signal and signal(SIGCONT, write_child); in child to cache signal . Am I correct ? – bholanath Oct 04 '13 at 05:25
also I have checked for Zombies while my program was stuck during execution(sometimes it successfully executes for 100 times as expected), there is no zombie. To see zombie I use top command and/or in other terminal ps aux | grep Z. – bholanath Oct 04 '13 at 05:37

Program hanged or stop execution randomly using fork() and signal

1 Answers1