Qiang has asked for the wisdom of the Perl Monks concerning the following question:

hi, i have piece of code utilizing Net::SNMP to query printers. sometimes it takes real long time to finish the query.I have used the -timeout and it doesn't appear do anything. now i am using eval and alarm but run into a problem. 

sub fun1 {

  foreach (printers ){
        my ($session, $error) = Net::SNMP->session(
              -hostname  => $ip,
              -community => chomp($cmnt),
              -port      => 161,
              -timeout   => 5,
        );

        my $result = $session->get_request(
              -varbindlist => [$OID]
        );

     eval {
        local $SIG{ALRM} = sub { die "alarm\n" }; 
        alarm 5;
            $result = $session->get_request(
                  -varbindlist => [$oid]
            );
        alarm 0;
        };
            $row .= lc($result->{$oid})."-";
   }
}

[download]
in the foreachloop, only the first loop times out within the eval block. the rest of loops takes less than 5 seconds to finish. however, after the first loop, $result->{$oid} is always empty. which isn't if i take out of the eval block. any idea ?

Replies are listed 'Best First'.
Re: eval alarm on mod_perl
by Roger (Parson) on Feb 18, 2004 at 07:15 UTC
    You code just added to the confusion. To start with, let's clarify your code a bit:

    - You have two get_request calls, one outside eval and one inside eval, is that how it looks in your script?

    - You are calling with different values of oid in the get_request, one is lowercase $oid, one is upper case $OID.
[reply]
      sorry about the confusion. here is the code in full. 
      
sub create_pr_table {

    my $get_pr_names = shift;
    my $row;
    # printer status
    my $OID = ".1.3.6.1.4.1.11.2.4.3.1.2.0";
    # LCD messages
    my @OIDs = (".1.3.6.1.2.1.43.16.5.1.2.1.1",
#        ".1.3.6.1.2.1.43.16.5.1.2.1.2",
#        ".1.3.6.1.2.1.43.16.5.1.2.1.3",
    );

    my $pr_section_name;
    # create the printer snmp info in html tag

    foreach $pr_section_name (values %{$config}) {

        my $pr_name = $pr_section_name->{pr_name};
        next unless $pr_name;
        $pr_names{$pr_name}="";
        # called from show_lpq_info and only need printer names info.
        next if $get_pr_names == 1;
        my $cmnt = $pr_section_name->{cmnt};
        my $ip = $pr_section_name->{ip};
        $row .= "<tr>";
        $row .= "<td nowrap><a href=index.pl?printer=$pr_name><font fa
+ce=\"arial\" size=2>$pr_name</font></a></td>";

        my ($session, $error) = Net::SNMP->session(
              -hostname  => $ip,
              -community => chomp($cmnt),
              -port      => 161,
              -timeout   => 5,
        );

        if (!defined($session)) {
              print STDERR $error;
              next;
        }

        # printer status row
        my $result = $session->get_request(
              -varbindlist => [$OID]
        );

        $row .= "<td nowrap><font face=\"arial\" size=2>".lc($result->
+{$OID})."&nbsp;</font></td>";

        # LCD messages
        $row .="<td nowrap><font face=\"arial\" size=2>";
        foreach my $oid (@OIDs) {

#eval {
#local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
#alarm 5;
            $result = $session->get_request(
                  -varbindlist => [$oid]
            );
#alarm 0;
#};
            $row .= lc($result->{$oid})."&nbsp;";
#           last if $result->{$oid} =~ m#powersave on#i;
        }
        $row .="</font></td>";

        # get this printer's queue
        my $queues = get_lpq_info($pr_name,1);
        $row .= "<td nowrap><center><font face=\"arial\" size=2>$queue
+s</font></center></td>";
        $row .= "</tr>";
    }
    return $row;
}

      [download]
      the eval part is commented out now. within every loop of the first foreach, it queries a printer for status etc via SNMP.
[reply]
[d/l]
Re: eval alarm on mod_perl
by simonm (Vicar) on Feb 18, 2004 at 19:37 UTC
    It may be that alarming out of the middle of a Net::SNMP operation causes that session to be left in an inconsistent state.

    You could test this by having the $SIG{ALRM} set a flag or clear out the $session, and then starting a new session before the next request.

[reply]

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