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# 1  
Old 09-06-2011
question about fork
i'm experimenting fork function and i found this code
Code:
#include <stdio.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <wait.h>
#include <fcntl.h>
#include <unistd.h>

int main(void)
{
	int fd[2];
	pid_t p;

	p = fork();
	fork();
	if (p>0) { fork();}
	fork();
	fork();
	sleep(30);
	exit(0);
}

I thought that there were 2^5 processes after running this code , but there were less processes.
Why?
Last edited by blob84; 09-06-2011 at 01:23 PM..
# 2  
Old 09-06-2011
Because when fork() returns, 2 processes exist: one parent, and one child.
  1. So after the first fork(), you have 2 processes.
  2. This 2 processes calls fork() again; you have now 4 processes.
  3. The third fork() is only performed by the children, resulting 4 more processes (now 6=4+2 in total).
  4. These 6 processes calls fork() twice, resulting 2*2*6 = 24 processes in total.
From this, it should be clear that several fork() one after the other causes an exponential growth of the number of processes.

Cheers,
/Lew
# 3  
Old 09-06-2011
The relationship between fork and the number of processes created isnt 2^n but 2n...and in this program it will be 2n-2 due to...if (p>0) { fork();}
This User Gave Thanks to shamrock For This Post:
zius_oram
# 4  
Old 09-06-2011
Quote:
The relationship between fork and the number of processes created isnt 2^n but 2n...and in this program it will be 2n-1 due to...if (p>0) { fork();}
May I suggest to check this assumption against reality by writing a small program?

Thanks,
/Lew
This User Gave Thanks to NH2 For This Post:
shamrock
# 5  
Old 09-06-2011
Quote:
Originally Posted by NH2
[*]The third fork() is only performed by the children, resulting 4 more processes (now 6=4+2 in total). [/LIST]
Non zero return value goes to parent not child...and after double cheking my calculations yes it will be 24 procs.
# 6  
Old 09-06-2011
Quote:
Originally Posted by shamrock
Non zero return value goes to parent not child...and after double cheking my calculations yes it will be 24 procs.
Thanks shamrock for double checking.

Cheers,
/Lew
# 7  
Old 09-10-2011
thanks NH2 for explanation!
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