Fork in Perl 5.8

[user2base]

I've found a script on the web that uses fork to run several pings in parallel. It works fine on a Linux box running perl 5.00x but it does not work on RedHat 8 with perl 5.8. Is it due to the new multi threading architecture in 5.8 ?
Moreover, I've read on this forum that you can not push results to an array within a fork because each child process is going to create a copy of this array: this tends to be confirmed when I tried to debug this under 5.8, however this script (that does push to an array) works very well on 5.00x

So how to have this working on 5.8 ?
Here is the script:
(PS: I have tried to do this using Parallel::ForkManager and I have the same issue.)


sub ping_a_host {
my $host = shift;
`ping -i 1 -c 1 $host 2>/dev/null` =~ /0 packets rec/ ? 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(&quot;Why did I see $pid ($?)\n&quot, next;
warn &quot;reaping $pid for $host\n&quot;;
$host_result{$host} = $? ? 0 : 1;
1;
}

my @hosts = map &quot;10.0.1.$_&quot;, &quot;001&quot;..&quot;254&quot;;

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

## final reap:
1 while wait_for_a_kid();

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

 

[justice41]

How does it not work under Perl 5.8? How does it fail and what is the error message? It ran for me under 5.6.1 and 5.8.0.

jaa

 

[user2base]

Actually I have slightly modified this script like this:
- using Net:ing (this should not make any difference)
- by pushing the result in an array within the last loop like this:

------------------------------------------
1 while wait_for_a_kid();
for (sort keys %host_result) {
if ($host_result{$_}){
push (@result, $_);
}
}
print &quot;at the end result = @result\n&quot;;
return @result;
------------------------------------------

It returns @result as empty even if I can see it equal to IP addresses that are pingable if I print its value within the fork loop it seems that this is effectively a &quot;copy&quot; that is used each time as the result of the print is:

at the end result =
result = 172.17.10.63
result = 172.17.10.70

Note the ordering.....


Actually I am now using Parallel::ForkManager to simplify the script but the result is the same (does not work on 5.8)
The script looks like:

------------------------------------------------
use Parallel::ForkManager;

my ($startip, $endip) = @_;
my @result;

my @octet = split (/\./, $startip);
my @hosts = map &quot;$octet[0].$octet[1].$octet[2].$_&quot;, &quot;$octet[3]&quot;..&quot;$endip&quot;;
my $ip;
my $pid;

$pm = new Parallel::ForkManager(10);

foreach $ip (@hosts) {
# Forks and returns the pid for the child:
$pid = $pm->start and next;
#... do some work with $data in the child process ...
if (ping_a_host($ip)){
push @result, $ip;
}
$pm->finish; # Terminates the child process
}

print @result;

------------------------------------------