Re: Need help with Perl multi threading

[Corion]

Please show the code and data that does "not work" for you. Please make it self-contained and about 20 to 25 lines long. Thank you.

[ashok.g]

Hi Corion,

Thanks for your reply. Main code:

#!/usr/bin/perl

use threads;
use strict;
use warnings;
use Net::SSH::Expect;
require 'total.pl';

my @servers = ('192.168.0.18','192.168.0.19','192.168.0.20');
my @process = ('testing','b','c');
my @threads;
my $output;
my $res;
foreach my $host ( @servers )
{
    my $png = `ping -c1 $host`;
    if ( $png =~ /64 bytes/ )
    {
        my $user= 'netcool';
                my $ssh = &SSH_Reference($host,$user);
        $ssh->run_ssh();
                eval {$res=$ssh->read_all(); };
        if ( !$@ && $res !~ /\(yes\/no\)/ && $res !~ m/password/ )
        {
            print "\nLogged in to $host\n";
                foreach my $proc ( @process ) 
                {
                    push (@threads, threads->new(\&Process_Output, $ss
+h, $proc ));
                    while ( my $thread = shift @threads )
                    {
                        $output=$thread->join();
                        #print @output;
                        if ( $output =~ m/$proc/ )
                                        {
                                                print "\t$proc is runn
+ing\n";
                                        }
                                        else
                                        {
                                                print "\t$proc is not 
+running\n";
                                        }
                    }
                }
            $ssh->close();
        }
        else
        {
            print "Unable to SSH to $host\n";
        }
    }
    else
    {
        print "\nUnable to ping to Host: $host\n";
    }
}

total.pl:

use Config::General;
use Tie::IxHash;
use Net::SNMP;

sub SSH_Reference()
{
    ($host,$user)=@_;
    #print "$host---$user--\n";
    #($host,$user)= @_;
    $ssh = Net::SSH::Expect->new (
        host => $host,
        user => $user,
        timeout=>10,
        raw_pty => 1
    );
    return $ssh;
}

sub Process_Output()
{
    $ssh = shift;
    $process = shift;
    #( $ssh, $process ) = @_;
    $output;
    $ssh->eat($ssh->peek(0));
    $ssh->send("ps -ef | grep $process | grep -v 'grep'");
    while ( defined ($line = $ssh->read_line(2)) )
    {
        next if ( $line =~ m/grep/ );
        $output .= "$line";
    }
    $ssh->eat($ssh->peek(0));
    return $output;
}

1;

And the output is:

perl some.pl 

Logged in to 192.168.0.18
Use of uninitialized value in pattern match (m//) at some.pl line 33.
    testing is not running
Thread 2 terminated abnormally: SSHConnectionAborted at total.pl line 
+25
Use of uninitialized value in pattern match (m//) at some.pl line 33.
    b is not running
Thread 3 terminated abnormally: SSHConnectionAborted at total.pl line 
+25
Use of uninitialized value in pattern match (m//) at some.pl line 33.
    c is not running

Logged in to 192.168.0.19
Segmentation fault

Please suggest

Thanks,
Ashok

[BrowserUk]

Sorry to be rude, but you really don't seem to have a clue what you are doing.

This is a completely redundant use of threading:

   push (@threads, threads->new(\&Process_Output, $ssh, $proc ));
   while ( $thread = shift @threads )
   {
       @output=$thread->join();
   }

You create a thread and push its handle onto @threads. You then immediately shift that handle off of the array and join it.

1. There is no point in using an array here, because it will only ever contain at most one handle.
2. Which makes using the while loop redundant because it will only ever iterate once.

   It is exactly equivalent to:

      $thread = threads->new(\&Process_Output, $ssh, $proc );
      if( $thread )
      {
          @output = $thread->join();
      }
   

   Which is equivalent to :

       $thread =  threads->new(\&Process_Output, $ssh, $proc );
       @output = $thread->join();
   

   Which is exactly equivalent to this:

       @output = threads->new(\&Process_Output, $ssh, $proc )->join();
   

   Which is exactly equivalent to:

      @output = Process_Output( $ssh, $proc );
   

   Except that the latter will work. (Of course, it won't speed things up. But neither will what you have now.) But it will work.

The reason your code is crashing is because you are creating an instance of Net::SSH::Expect in one thread, and trying to use it in another.

Why? Why not create the object in the thread where you are going to use it?

[ashok.g]

Thanks for your explanation!

So, you mean to say keep the thread that will do all like creating a SSH reference, calling function and what not for each server....?

This is exactly what I started with but I thought thread is having some problems with SSH (a dumb guess) and ignored that.

I will try that and will post you my findings.

Thanks,
Ashok.

[ashok.g]

Now this code:

#!/usr/bin/perl

use threads;
use strict;
use warnings;
use Net::SSH::Expect;
require 'total.pl';

my @servers = ('192.168.0.18','192.168.0.19','192.168.0.20');
my @process = ('testing','b','c');
my @threads;
my $output;
my $res;
my $final;
#@output = threads->new(\&Process_Output, $ssh, $proc )->join();

foreach my $host ( @servers )
{
    threads->new(\&process, $host )->join();
}
sub process()
{
    my $host = shift;
    my $png = `ping -c1 $host`;
    if ( $png =~ /64 bytes/ )
    {
        my $user= 'netcool';
                my $ssh = &SSH_Reference($host,$user);
        $ssh->run_ssh();
                eval {$res=$ssh->read_all(); };
        if ( !$@ && $res !~ /\(yes\/no\)/ && $res !~ m/password/ )
        {
            print "\nLogged in to $host\n";
                foreach my $proc ( @process ) 
                {
                    #push (@threads, threads->new(\&Process_Output, $s
+sh, $proc ));
                    $output=&Process_Output($ssh, $proc );
                        #print @output;
                        if ( $output =~ m/$proc/ )
                                        {
                                                print "\t$proc is runn
+ing\n";
                                        }
                                        else
                                        {
                                                print "\t$proc is not 
+running\n";
                                        }
                }
            $ssh->close();
        }
        else
        {
            print "Unable to SSH to $host\n";
        }
    }
    else
    {
        print "\nUnable to ping to Host: $host\n";
    }
}

produces this output:

perl some.pl 
Unable to SSH to 192.168.0.18
Unable to SSH to 192.168.0.19
Unable to SSH to 192.168.0.20

Now again back to the stage where I have started my script....

[Eliya]

I suspect your main problem is that you're trying to use the same instance of the SSH connection in all threads.  Creating a new thread doesn't automagically also create a new independent duplicate of the connection (socket, server-side process, and all), so the SSH will probably get mildly confused when multiple clients are talking simultaneously on the same line...

[Anonymous Monk]

The first, most obvious problem is that you did not use warnings; use strict;

I see undeclared variables and other weird stuff. What's "$output;" all by itself in the middle of the function supposed to do anyways?

[ashok.g]

Ok. I have modified the code and new output now.