Or both? :)

I am trying to use fork() for the first time, via merlyn's column Doing many things, like pings. However, I am trying to do this on ActiveState Perl (5.8.8) on Windows XP, and am not sure if that is the cause of my problem.

Here is my code (well, merlyn's with OS-specific modifications):

#!/perl/bin/perl
use warnings;
use strict;

sub ping_a_host {
  my $host = shift;
  `ping -n 1 -w 1 $host 2>NUL` =~ /Received = 0/ ? 0 : 1;
}

my %pid_to_host;
my %host_result;

sub wait_for_a_kid {
  my $pid = wait;
  return 0 if $pid < 0;
  my $host = delete $pid_to_host{$pid}
    or warn("Why did I see $pid ($?)\n"), next;
  warn "reaping $pid for $host\n";
  $host_result{$host} = $? ? 0 : 1;
  1;
}

my @hosts = map "10.0.1.$_", "025".."026";

for (@hosts) {
  wait_for_a_kid() if keys %pid_to_host > 10;
  if (my $pid = fork) {
    ## parent does...
    $pid_to_host{$pid} = $_;
    warn "$pid is processing $_\n";
  } else { # child does
    ## child does...
    exit !ping_a_host($_);
  }
}

## final reap:
1 while wait_for_a_kid();

for (sort keys %host_result) {
  print "$_ is ", ($host_result{$_} ? "good" : "bad"), "\n";
}

[download]

The code runs, however there are two problems I've noticed. 1) The final print statement never prints, regardless of the system state. 2) If the IP is not up, the process never finishes; it outputs:

C:\Scripts\Parallel>ping_parallel.pl
-3676 is processing 10.0.1.025
-3072 is processing 10.0.1.026

[download]

and then sits there. Any ideas what may be wrong?

In reply to Windows fork problem or my ignorance? by romandas

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