CODEWITHSUNDEEP
linuxwindowscygwinforkpid
Muhannad
Muhannad

Reputation: 455

is Fork() different in Cygwin (on Windows) and Linux

I'm using this code in both Linux and in Cygwin (on Windows) and the output order is different and I have no clue why..

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



int main()
{
        pid_t pid;

        /* fork a child process */
        pid = fork();

        printf("\n PID1 %d\n",pid);

        pid = fork();

        printf("\n PID2 %d\n",pid);

        return 0;
}

the output in windows is:

 PID1 3888

 PID1 0


 PID2 5564
 PID2 7772

 PID2 0

 PID2 0

but in Linux (and MAC) it looks like

PID1 2486

 PID2 2487

 PID2 0

 PID1 0

 PID2 2488

 PID2 0

My question is PID2 ( PID2 2487) comes before PID1 in Linux but not in Windows (the output behavior is the same every time I run the code)

Upvotes: 0

Views: 3459

Answers (2)

GingerJack
GingerJack

Reputation: 3134

After a fork(), it is indeterminate which process—the parent or the child—next has access to the CPU.On a multiprocessor system, they may both simultaneously get access to a CPU.An operating system can allow you to control this order. For instance, Linux has /proc/sys/kernel/sched_child_runs_first.

Upvotes: 4

nneonneo
nneonneo

Reputation: 179687

The order in which the processes run in post-fork is unspecified.

Upvotes: 3

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