Problem removing handlers via fileevent

[joeb1234567]

Apologies if this isn't the correct place to be reporting this issue. If that's the case, I'd be grateful if someone would point me in the right direction.

I have recently been blowing the dust off a Perl/Tk application that I wrote some 20 years ago. I'm pretty sure it was working properly back then, but I tried it against the the perl-tk package in Debian Bookworm (version 1:804.036-1+b2) and it doesn't work as expected.

I have narrowed the problem down to the way fileevent behaves. My application uses a socket and always needs a 'readable' event handler and creates a 'writable' event handler as and when it needs it. So it's regularly calling fileevent to both set and unset the 'writable' event handler.

What I'm seeing with the version of Perl/Tk that I've been using is that when the 'writable' event handler is removed, the 'readable' event handler is also removed. I can work around this behaviour by retrieving the 'readable' event handler before removing the 'writable' one and then re-setting the 'readable' handler.

Here's a script that shows the problem for me:

#!/usr/bin/perl
use strict;
use IO::Socket;
use Tk;

my $mw = MainWindow->new;

sub printHandlers {
    my $sock = shift;

    my $ret = $mw->fileevent($sock, 'readable');
    print("readable: ${ret}\n");

    $ret = $mw->fileevent($sock, 'writable');
    print("writable: ${ret}\n");
}

my $sock = IO::Socket::INET->new (PeerAddr => 'google.com', PeerPort => 80, Proto    => 'tcp');
print "No handlers set...\n";
printHandlers($sock);

$mw->fileevent($sock, 'readable' => sub {});
$mw->fileevent($sock, 'writable' => sub {});
print "\nBoth readable and writable handlers set...\n";
printHandlers($sock);

$mw->fileevent($sock, 'readable' => '');
print "\nReadable handler removed...\n";
printHandlers($sock);

I see the following output:

No handlers set...
readable: 
writable: 

Both readable and writable handlers set...
readable: Tk::Callback=ARRAY(0x556871a43960)
writable: Tk::Callback=ARRAY(0x5568718188a8)

Readable handler removed...
readable: 
writable: 

I would expect the last line of the above output to show a 'writable' handler because only the 'readable' handler was removed.

Interestingly, the following Tcl/Tk script doesn't show this behaviour:

#!/usr/bin/wish

proc readHandler sock {
}

proc writeHandler sock {
}

proc printHandlers sock {
    set ret [fileevent $sock readable]
    puts "readable: ${ret}"
    set ret [fileevent $sock writable]
    puts "writable: ${ret}"
}

set sock [socket "google.com" 80]
puts "No handlers set..."
printHandlers $sock

fileevent $sock readable [list readHandler $sock]
fileevent $sock writable [list writeHandler $sock]
puts ""
puts "Both readable and writable handlers set..."
printHandlers $sock

fileevent $sock readable ""
puts ""
puts "Readble handler removed..."
printHandlers $sock

exit

I see the following output:

No handlers set...
readable: 
writable: 

Both readable and writable handlers set...
readable: readHandler sock55ab4d96fc90
writable: writeHandler sock55ab4d96fc90

Readble handler removed...
readable: 
writable: writeHandler sock55ab4d96fc90

This seems correct to me. Perhaps I'm using the Perl/Tk interface incorrectly. If that's the case I'd be interested to know what I'm doing wrong. Thanks.