Array getting destroyed when thread exits in perl - multithreading

Question

I was trying to use threading for parsing two different types of files. The subroutines share no data at all.
# Parse header files
$hdr_thrd = threads -> create(\&Parser::parse_header_file, $path);
# Parse input template files
$tmplt_thrd = threads -> create(\&TemplateParser::parse_template);
# Join the threads
$tmplt_thrd -> join();
$hdr_thrd -> join();
# This uses the data obtained from the above two threads
&Parser::parse_xml_template();
The problem comes when the parse_xml_template function tries to access an array #TemplateParser::array. The array has no data at this point but it is getting filled inside the parse_template function. Am I missing something?

Answer 1

You're trying to share data across threads without sharing it. You need to use :shared or share() on the variable.
You wouldn't have this problem at all if you were to avoid global vars as you should.
sub parse_template {
my #tmplt_result;
...
return \#tmplt_result;
}
my $hdr_thrd = threads->create(\&Parser::parse_header_file, $path);
my $tmplt_thrd = threads->create(\&TemplateParser::parse_template);
my $tmplt_result = $tmplt_thrd->join();
my $hdr_result = $hdr_thrd->join();
(Explicit sharing is not necessary to when returning a value via join.)
Of course, that needlessly creates two threads (for a total of three) when two would suffice. Instead, you could use:
sub parse_template {
my #tmplt_result;
...
return \#tmplt_result;
}
my $hdr_thrd = threads->create(\&Parser::parse_header_file, $path);
my $tmplt_result = TemplateParser::parse_template();
my $hdr_result = $hdr_thrd->join();