Process Scheduling using fork()

Hi I have to accomplish the following:

Write a program that will consider the effects of process scheduling by using fork() system call. The write() system call is used instead of printf. The sleep() system call is used to prevent the process from running to completion within one slice time. Compile and run your program so it will output as follows:

Parent
Parent
Child
Parent
Child
Parent
Child
Parent
Child
Child

I would appreciate any help on this, I'm not sure what the fork() system call does and how to integrate it in a program.

Do you have any code to work with at all yet? Also, if your getting a programming assignment on a specific function, I would have guessed they had explained what it was for to start with. If your really stuck, you might want to talk to your teacher.

It's an operating systems class there's no code that we learned whatsoever which sucks, I have no examples to reference.

Search references on fork() on google, or try "man fork" in unix

I searched for some examples and I'm trying to compile one and I'm getting an error saying: "fatal error C1083: Cannot open include file: 'unistd.h': No such file or directory
Error executing cl.exe." here's the code:

Code:

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#include <iostream>
using namespace std;
#include <sys/types.h>
#include <unistd.h>

int main(void) {

        pid_t childpid;

        childpid = fork();
        for (int i = 0;  i < 5;  i++) {
                cout << "This is process " << getpid() << endl;
                /* sleep is a system call or library function that suspends
                  this process for the indicated number of seconds */
                sleep(2);
        }

        return 0;
}

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You need to compile your code on some kind of unix system - Windows/MS compiler don't do fork().

> Compile and run your program so it will output as follows:
Unless you're prepared to sleep() for days at a time, there is no real way to ensure that two independent processes will remain synchronised such that it's guaranteed that they'll always produce the same output.

Quote:

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Originally Posted by Salem

> Compile and run your program so it will output as follows:
Unless you're prepared to sleep() for days at a time, there is no real way to ensure that two independent processes will remain synchronised such that it's guaranteed that they'll always produce the same output.

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I know with threads you can do seamophores(SP) and mutexes. You could use a pointer you declare in the main, and have it check if one has printed and the other hasn't. Like if the value the pointer points to equals anything but 0, the parent has printed its message, and if it equals 0, the child has. You can tell which is the parent and the child based on what fork returns (I believe its the pid to the parent, 0 to the child).

yes you're correct Xipher thank you.