Can't use Net::Appliance::Session inside a thread

Posted on 2008-01-22 12:41:21-08 by miky

Hello, I'm not sure it's a Net::Appliance::Session related problem but I just wanted to have your opinion. So far I'm using Net::Telnet and Net::Telnet::Cisco and threads, everything is working fine. When I use Net::Appliance::Session launched by a thread it segfaults. I wrote this little script that reflects my problem and which is more simple that the script I use.

#!/usr/bin/perl

use Net::Appliance::Session;
use threads;
use threads::shared;

$ip='10.1.1.1';
$host='ROUTER1';
$pf='MyPTF';
$device='cisco_router';
$connexion='ssh';
$login='miky';
$pass='mypass';
$enable='';
my $num_threads : shared = 0;
my $max_thread = 1;

while ($num_threads >= $max_thread)
{
  print "$num_threads thread(s) actifs: nombre de threads maximal autorise atteint\n";
  sleep 2;
}
$num_threads++;

my $thr = threads->new('net_ssh_cisco', $ip, $host, $pf, $device, $login, $pass, $enable);
$thr->detach();
sleep 2;

sub net_ssh_cisco
{
  my ($ip, $host, $pf, $device, $login, $pass, $enable) = @_;
  my $session;

  eval { $session = Net::Appliance::Session->new( Host => $ip, Transport => 'SSH' ); };
  if ($@)
  {
    print "$@\n";
    print "$host injoignable\n";
    $num_threads--;
    return;
  }
  print "Connexion effective\n";

  eval { $session->connect(Name=>$login, Password=>$pass); }; # <<< Problem is here
  if ($@)
  {
    print "$@\n"; # <<< Debug message
    print "$host probleme de password\n"; # <<< Debug message
    return;
  }
  print "Logged on ";
  print "$host\n";
  $session->close;

  $num_threads--;
}

When I execute the script

$ ./debugthread.pl

Connexion effective
Failed to get first prompt at ./debugthread.pl line 58
ROUTER1 probleme de password
Segmentation fault

It seems that this message comes from Net/Appliance/Session/Transport/SSH.pm

my $match;
(undef, $match) = $self->waitfor($self->pb->fetch('userpass_prompt'))
            or $self->error('Failed to get first prompt');

When I don't use threads it works, with threads it doesn't. Do you have an idea of what happens or could you point out a direction that could help ? Thanx

Posted on 2008-01-31 22:33:06-08 by oliver in response to 6909

Hi Miky,

I don't have a lot of experience with threads, but I did run your sample program (thanks for that!) and made a little investigation.

My best guess is that this is a problem with the Net::Telnet module. My reason for reaching this conclusion is that the error message returned, "Failed to get first prompt", is returned immediately after the connect() method is called. There should be a 10 second timeout on this, waiting for the prompt. The timeout actually happens within the waitfor() method of Net::Telnet, so I think it's this which is not thread safe. For some reason it does not wait 10 seconds but instead returns immediately with a failure. Perhaps it is some problem with signal handling?

Unfortunately, the loop which has the "broken" timeout in Net::Telnet is generated code, so it's hard to debug, and also because I am not an experienced threads programmer I wouldn't know where to start anyway.

For now, I think we are going to have to say that Net::Appliance::Session is not thread safe, because of this problem. I'm very sorry about that.

regards, oliver.

Posted on 2008-02-01 00:37:14-08 by onishin in response to 6985

I have same pb for mode Telnet . My solution is run another process perl for just one connexions. 1 Have 1 script ( Main ) run Many another for processe Net:Telnet Main:

foreach my $id (@routeur) { exec child.pl $id ; }

(This article is based on a thread on the CPAN::Forum.)