Question

I’m having a hard time with this problem, but I’ve narrowed it down to using XML::LibXML after I’ve done a fork in Perl. I’m running Strawberry Perl 5.12.0 on Windows XP, and XML::LibXML 1.70.

I’m have a script where I need to run several processes concurrently, take the XML output and process the results. If I run this on a Solaris machine, it runs just fine and I have no issues. However, if I run this on Windows, I get a crash window stating that ‘perl.exe has encountered a problem and needs to close.’

Here is a sample program that will generate the error:

use strict;
use warnings;
use XML::LibXML;
use Try::Tiny;

my $cmds = ['cmd1', 'cmd2'];
my @pids = ();
foreach my $cmd (@{$cmds}) {

    my $pid = fork();

    if ($pid) {

        # parent
        push (@pids, $pid);
    } elsif ($pid == 0) {

        XML::LibXML->load_xml(string=>'<root />'); # <-- this will crash it
        exit 0;
    }
}

foreach my $ch_pid (@pids) {

    try {

        waitpid($ch_pid, 0);
    } catch {

        carp("Error on waitpid: $!");
    };
}
exit 0;

If I only have one process, or if I don’t fork, then it will work successfully. If I remove the load_xml call (and have nothing in the child), then it will work successfully.

Does anyone know what may be causing this and how to fix it?

Answer 1

Special considerations need to be made when using XML::LibXML with threads. Some of these (particularly about initially loading the module) will also pertain to forks.

You can try removing the compile time load (the use XML::LibXML; line), and instead load in the module once you have forked:

} elsif ($pid == 0) {
    require XML::LibXML;
    XML::LibXML->load_xml(string=>'<root />');
    exit 0;
}