Change:

use Win32::GUI();

my $text;
[download]

To:

use threads; use threads::shared;
use Win32::GUI();

my $text :shared;
[download]

And see what happens.

BrowserUK, thanks for pointing out that Win32::GUI::Dialog() is actually a loop!

I tried the following and it seems to almost get what I was expecting:

            while(1){
             $display->Show();
             $display->SelectAll();
             $display->Clear();
             $display->Update();
             $display->Append($text);
             $display->Update();
             sleep(10);
            }
             Win32::GUI::Dialog();
[download]

The problem is: the cursor is always busy because of Win32::GUI::Dialog(); loop.

The dialog call is now reduntant. Try this:

use strict;
use warnings;
use threads; use threads::shared;
use Win32::GUI();

my $text :shared;
my @h = qw(LINE1 LINE2 LINE3 LINE4 LINE5);

my $pid = fork();
if ($pid){
    my $main = Win32::GUI::Window->new(
        -left   => 100,
        -top    => 100,
        -width  => 310,
        -height => 150,
    );
    $main->Show();
    my $display = $main->AddTextfield(
        -left   => 60,
        -top    => 35,
        -width  => 180,
        -height => 20,
    );
    while(1){
         $display->Show();
         $display->SelectAll();
         $display->Clear();
#         $display->Update();
         $display->Append($text);
         $display->Update();
         sleep(1);
    }
}
elsif ($pid == 0) {
    while(1){
        $text = "$h[int(rand(@h))]";
        sleep(1);
    }
}
[download]

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"I'd rather go naked than blow up my ass"

BrowserUk, Thanks for the pointer. Now looks like the value of $text can successfully be passed to the parent at some point. But somehow this $text is not dynamically changing. I'm expecting $text can be dynamically displayed and that's why I created two infinite loops in both child and parent.

Anyway, thanks again :)

The problem is, this Win32::GUI::Dialog(); is a loop. It doesn't return until you do something on the dialog. If you click the close button on the dialog a few times, you'll see that the child is indeed running its loop.

But until you understand how Win32::GUI works, trying to write multi-threaded apps using it is going to be a frustrating exercise.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"I'd rather go naked than blow up my ass"

or what I might be doing terribly wrong?

Processes do not share variables. Once you fork(), each process has its own copy of the variables, and any changes to the variables are local to the process. The subject you need to research is IPC (inter process communication). You might start by reading perlipc.

Here is an example of what you can do:

use strict;
use warnings;
use 5.010;


my @lines = qw{ LINE1 LINE2 LINE3 LINE4 LINE5 };

my $pid =  open my $INPUT_FROM_CHILD, '-|';

if (!defined $pid) {
    die "Couldn't fork: $!";
}

if ($pid) {
    say 'parent: blocking until child sends some data...';
    while (<$INPUT_FROM_CHILD>) {  #line oriented reading
        chomp;
        say "parent: $_";
    }

    waitpid($pid, 0);
    say "parent: child exited with status = $?";
    say 'parent: exiting...';
}
else {
    sleep 2;

    say $lines[int(rand(@lines))];
    close $INPUT_FROM_CHILD;

    sleep 10;
}
[download]

Processes do not share variables. Once you fork(), each process has its own copy of the variables,

Under win32, fork is just threads::create() in disguise.

---

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

"I'd rather go naked than blow up my ass"

...which also does not share variables. Each thread has its own copy of the variables.

forks::shared and threads::shared does allow sharing.

@7stud, thanks for pointing this out: "Processes do not share variables". I think this is the crux of my problem. I'll take a look at perlipc. Thanks :)

BTW, I'm running ActivePerl on Windows box, your illustration code has this "open my $INPUT_FROM_CHILD, '-|';", which does not work for me. But thanks the same :)