Oh sagacious and munificent monks;

In my eternal attempt to better myself, I've been trying to learn threads under Perl. I wrote the following code to play with concepts in message dispatching. Ideally, it should just echo input back at me until I 'quit'. It behaves nicely on my Linux box (5.8.8 64-bit multithread under Debian) but hangs on my Windows box (ActiveState perl v5.8.8 MSWin32-x86-multi-thread on a dual-core) on line 26 on the first invocation. Any ideas on routes I could pursue to fix this?

#!/usr/bin/perl
use strict;
use warnings;
use threads;
use Thread::Queue;

# Create terminal watcher
print "Create terminal watcher...\n";
my $Q_stdin = Thread::Queue->new;
async {
        $Q_stdin->enqueue( $_ ) while defined( $_ = <STDIN> );
    }->detach;
my $Q_found = Thread::Queue->new;

my $cmd;
print "Awaiting commands...\n";
MAIN_LOOP: while (not defined $cmd or $cmd !~ /^q/i) {
    sleep(1); # Reduce load
    # Process commands
    $cmd = $Q_stdin->dequeue_nb;
    if (defined $cmd) {
        chomp $cmd;
        if ($cmd =~ /^q/i) {
            print "Resolving open threads\n";
        } else {
            async {
                    $Q_found->enqueue( $cmd ) ;
                }->detach;
            #$Q_found->enqueue( $cmd ) ; # using this in place of asyn
+c works
        }
    }
    # Print announcements
    while (defined(my $output = $Q_found->dequeue_nb)) {
        print $output, "\n";
    }
}

[download]

Update: The issue can be resolved by ensuring STDIN is closed before entering MAIN_LOOP (thanks oshalla). The reason for it is still not entirely clear in my mind, but I have some clear avenues of research to pursue - there seem to be both OS and Perl version variations impacting the behaviors of this code. In any case, a more verbose version that behaves as expected follows:

#!/usr/bin/perl
use strict;
use warnings;
use threads;
use Thread::Queue;
use Thread::Semaphore;

# Create terminal watcher

print "Create terminal watcher...\n";

my $Q_stdin = Thread::Queue->new ;
my $S_stdin = Thread::Semaphore->new(0) ;

print "fileno(STDIN) = ", fileno(STDIN), "\n" ;

async {
    $S_stdin->down() ;
    print "Reading STDIN, fileno=", fileno(STDIN), "\n" ;
    while (defined( $_ = <STDIN> )) {
        chomp ;
        print "\n+IN : '$_'\n" ;
        $Q_stdin->enqueue( $_ ) ;
    };
}->detach;

close STDIN ;                          ### no longer our business     
+  <<<<
print "STDIN is: ", defined(fileno(STDIN)) ? 'open' : 'closed', "\n" ;

$S_stdin->up() ;
my $Q_found = Thread::Queue->new;

my $cmd;
my $quit_flag = 1;
print "Awaiting commands...\n";
MAIN_LOOP: while ($quit_flag) {
    sleep(1); # Reduce load
    # Process commands
    while (defined ($cmd = $Q_stdin->dequeue_nb)) {
        chomp $cmd;
        if ($cmd =~ /^q/i) {
            print "Resolving open threads\n";
            $quit_flag = 0;
        } else {
            async {
                  $Q_found->enqueue( $cmd ) ;
                }->detach;
            #$Q_found->enqueue( $cmd ) ; # using this in place of asyn
+c works
        }
    }
    # Print announcements
    while (defined(my $output = $Q_found->dequeue_nb)) {
        print "+OUT: '$output'\n";
    }
}

[download]

In reply to threads on Windows by kennethk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.