Dear All,

How reliable is multithreading?

The reason why I ask is this. I found this bit of code here which suppose to ping a list of host name concurrently.

use strict;
use threads;
use Thread::Queue;
use Net::Ping;
my $ThreadCount = 6;
my @Threads;
my $ServerQueue = Thread::Queue->new;
my @down;

chomp (my @Servers = <DATA>);
foreach my $Item (@Servers) 
{ 
    $ServerQueue->enqueue($Item);
}
for (1..$ThreadCount) 
{
    my $Thread = threads->new(\&Process, $ServerQueue);
    push (@Threads, $Thread);
}
my $Start_time = time;
foreach my $Thread (@Threads) 
{
    $Thread->join();
}
my $End_time = time;
print "Start : $Start_time\n";
print "End : $End_time\n";
my $lapsed = $End_time - $Start_time; 
print "\n\nLapsed Time (in Seconds) : $lapsed\n";
print "\n\n_________________\n\n";
print "$_\n" for @down;
sub Process 
{
    my $ServerQueue = shift;
    my $pingobj = Net::Ping->new("icmp",5,64);
    while (1) 
    {
        my $Server = $ServerQueue->dequeue_nb();
        last if (! $Server);
        if ($pingobj->ping($Server)) 
        {
            print "$Server : Up\n";
        }
        else 
        {
            push (@down, $Server . " : Down");
        }
    }
}


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Which it does but not accurately. i.e. the script will report a machine is up even when its down!

How do I know this? Because I wrote this poxy script - see below - to do the same but sequentially and its 100% accurate.

Here is the code

use strict;
my @down;
chomp (my @Servers = <DATA>);
my $Start_time = time;
foreach (@Servers) 
{
   my $res = `ping -n 1 $_`;
   if ($res =~ /reply/i)   
   {
      print "$_ : Up\n";
   }
   else
   {
      push (@down, $_." : Down");
   }
}
my $End_time = time;
print "Start : $Start_time\n";
print "End : $End_time\n";
my $lapsed = $End_time - $Start_time; 
print "\n\nLapsed Time (in Seconds) : $lapsed\n";
print "\n\n\n___________________________\n\n\n";
print "$_\n" for @down;


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Can an angle please advise why this state of the art module fails when a script that was written without any thoughts does much better job?

Thanks

BTW: in the multithreaded script what does this mean/do? my $ThreadCount = 6;