Re: Problems forking -- fork DOSes my comp

[George Schlossnagle]

On Dec 10, 2003, at 4:52 PM, Dan Anderson wrote:

I am learning about forks, so I tried the following code to make sure I
had everything down:
#! /usr/bin/perl

use strict;
use warnings;
my $counter = 1;
my $pid = 0;
while ($counter < 50) {
  if ($pid = fork) {
    open ("FORKED", ">./fork/$counter")
      or die("COULD NOT OPEN FORK");
    print FORKED $counter;
    close("FORKED");
    $SIG{CHLD} = "IGNORE";
  }
  $counter++;
}


Two major problems:

o You are not closing your children when they are done with their 
tasks, meaning that they re-enter the while() loop and fork new 
children themselves. (this is why you fork-bombed your box)
o You are doing the work in the parent, not in the child

you want something like this:

$SIG{CHLD} = "IGNORE";
for my $counter(0...50) {
  my $pid = fork();
  if($pid == 0) { # child
    open FORKED, ">./fork/$counter"
      or die("COULD NOT OPEN ./fork/$counter");
    print FORKED $counter;
    close("FORKED");
    exit;  # critical to exit here, else this child will spawn new 
children itself
  }
}

// George Schlossnagle
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