Random numbers in parent/child?

Thread Tools Search this Thread
Top Forums Programming Random numbers in parent/child?
# 1  
Old 09-27-2009
Random numbers in parent/child?


I'm trying to generate random numbers both in parent process and the child process. But I get the same random number in both processes. Why doesn't it generate different numbers altough I seed random number generator?
Here's my code:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>

void seedit(void)
    struct timeval tv;
    gettimeofday(&tv, NULL);
    srand(tv.tv_sec * tv.tv_usec);

int main()
        int pid;
        pid = fork();
        if (pid==0)
                int r = rand()%10 + 1;
                printf("[CHILD] sleeping %d sec\n", r);
        else if (pid>0)
                int r = rand()%10 + 1;
                printf("[PARENT] sleeping %d sec\n", r);

# 2  
Old 09-27-2009
Probably the srand/rand functions use some kind of internal state which is bound to the process. When you call fork, the whole process is duplicated, including the state of the randomizer. Either seed it for each process seperately, or use some independent random source (like /dev/random).
# 3  
Old 09-27-2009
Because the child process has the exact same seed value as the parent.

Move the srand statment down inside the if(pid ... ) blocks.
Use two different prime numbers say: 13 and 8191. Then you will get different values.
Time as a ssed may not necessarily work - you can try calling seedit() down inside the if blocks if you want to test how well it works.
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

parent and child directory

does anyone know how to check in an 'if' statement if a particular directory is a child directory of a particular directory? help ~ (2 Replies)
Discussion started by: ymc1g11
2 Replies

2. Shell Programming and Scripting

forking a child process and kill its parent to show that child process has init() as its parent

Hi everyone i am very new to linux , working on bash shell. I am trying to solve the given problem 1. Create a process and then create children using fork 2. Check the Status of the application for successful running. 3. Kill all the process(threads) except parent and first child... (2 Replies)
Discussion started by: vizz_k
2 Replies

3. Homework & Coursework Questions

Need help with deleting childīs parent and child subprocess

1. The problem statement, all variables and given/known data: I need to make an program that in a loop creates one parent and five children with fork(). The problem i'm trying to solve is how to delete the parent and child of the childīs process. 2. Relevant commands, code, scripts,... (0 Replies)
Discussion started by: WhiteFace
0 Replies

4. Programming

To share fd between parent and child

i used function fork(). so i made two process. parent process accepted socket fd and writing to shared memory. then now. how can child process share parent's socket fd? is this possible? Thanks in advance (1 Reply)
Discussion started by: andrew.paul
1 Replies

5. UNIX for Advanced & Expert Users

Child Killing Parent

Hi all, I am writing a script which calls other third party scripts that perform numerous actions. I have no control over these scripts. My problem is, one of these scripts seems to execute and do what it is meant to do, but my calling / parent script always exits at that point. I need to... (4 Replies)
Discussion started by: mark007
4 Replies

6. Shell Programming and Scripting

exiting a child without stopping the parent

Greets all. This is using bash/sh on Slackware Linux 12.... I have a parent and MANY children scripts. The parent would be: for script in scripts/*.sh; do sh $script || exit 1 done I'm trying to get a child script to quit running without bombing my parent script. This would be the... (5 Replies)
Discussion started by: madpenguin
5 Replies

7. Shell Programming and Scripting

Parent/Child Processes

Hello. I have a global function name func1() that I am sourcing in from script A. I call the function from script B. Is there a way to find out which script called func1() dynamically so that the func1() can report it in the event there are errors? Thanks (2 Replies)
Discussion started by: yoi2hot4ya
2 Replies

8. UNIX for Dummies Questions & Answers

kill parent and child

Hello all, I have gone through the search and looked at posting about idle users and killing processes. Here is my question I would like to kill an idle user ( which I can do) but how can I asure that all of his process is also killed whit out tracing his inital start PID. I have tried this on a... (4 Replies)
Discussion started by: larry
4 Replies

9. Filesystems, Disks and Memory

How hard can it be? ps child/parent

:( Since I'm fairly new to the scene and don't have much experience in shell programming, I decided to check out the net for a useful script or two. What I'm looking for is a script that would let me enter a PID and then show the process tree associated with it. So it would display the (grand-)... (2 Replies)
Discussion started by: velde046
2 Replies

10. UNIX for Dummies Questions & Answers

what are parent and child processes all about?

I don't follow what these are... this is what my text says... "When a process is started, a duplicate of that process is created. This new process is called the child and the process that created it is called the parent. The child process then replaces the copy for the code the parent... (1 Reply)
Discussion started by: xyyz
1 Replies
Login or Register to Ask a Question