[Expectperl-discuss] Another threading question

[POMvR <po...@po...>]

Hey folks.  I've really appreciated the posts in this forum, as they have
gotten me past the initial roadblocks to getting Expect to work in a
threaded PERL application.  Unfortunately, I've hit a bit of a snag and I
thought I'd post the problem here to see if anyone's experienced the same
type of issue.  Following what's been suggested here, I'm creating my
initial Expect objects in the main thread and establishing ssh connections
to the load balancers I need.  I'm passing these objects to a handful of
boss threads, which first loop through a set of servers to remove them from
the load balancer via Expect.  Each boss thread then creates a pool of child
threads that issue commands against this same set of servers and doesn't use
Expect (or the connection object).  The code works great on the first set of
servers, but after I join the first group of threads and they finish, the
second set is returning undefined for all the expect(...) calls.  What makes
this so strange is that if I turn on debugging for Expect, it works fine
(although it floods STDOUT).  I've tried a number of things to try and solve
the problem (flushing STDOUT, calling clear_accum(), turning on warnings and
diagnostics).  The only hint of what's going on came through diagnostics,
which throws the following error when the problems start to occur:

print() on closed filehandle GEN0 at
        /usr/lib/perl5/5.8.0/i386-linux-thread-multi/IO/Handle.pm line 395,
<STDIN> line 3 (#1)
    (W closed) The filehandle you're printing on got itself closed sometime
    before now.  Check your control flow.

Here's a simplified version of the code from the boss thread that appears to
be causing problems:

# First remove all the servers from the load balancer pool
foreach my $serv (@server_stack) {
    $result = &run_command($expect_connection,"disable $serv");
}
# Run some commands against this set of servers now that they're out of the
pool
my @threads = ();
while (@server_stack) {
        my $server = pop(@server_stack);
        push @threads, threads->new(\&shutdown_server,$server);
}
foreach my $thr (@threads) {
    @return_vals = (@return_vals, $thr->join());
}
foreach my $thr (@threads) {
    undef $thr;
}

Since I'm using PERL 5.8.0, I'm undef'ing the threads once they are
finished, since there were some issues with this in 5.8.0.  This code block
runs fine the first time, but as soon as I send it a new @server_stack, the
calls to &run_command no longer work.  Here's what run_command looks like:

sub run_command {
    my($proc, $command) = @_;
    my $timeout = 6;
    $proc->raw_pty(1);
    $proc->log_stdout(0);
    $proc->log_file("temp.log");
    $proc->debug(0);
    $proc->send("$command\r");
    my $i = $proc->expect($timeout, "-re", " # ");
    if (!(defined $i)) {
        return "ERROR: no response to command!\n";
    }
    return $proc->before();
}

However, if I set $proc->debug(4), it works fine, albeit a bit ugly to
watch.  It almost seems like something is closing the filehandle that the
Expect connection object is using after the first thread group finishes,
even though the thread group isn't even operating on the connection object. 
I apologize for only posting snippets, but there is too much code to post
otherwise.  I'm getting this system upgraded to PERL 5.8.8, but it's not
going to be anytime soon, so I'm trying to make this work with what I've
got.

If anyone has experienced something similar or has an idea what might fix
this, it would be much appreciated.  I've been pulling my hair out on this
one for a while now.  Thanks for listening.

-Phil
-- 
View this message in context: http://www.nabble.com/Another-threading-question-tf4559826.html#a13012890
Sent from the Perl - Expectperl-Discuss mailing list archive at Nabble.com.