Perl threads, sockets and STDIN interference - multithreading

Question

I am trying to use a perl threads and sockets, to create a simple client/server application. The problem comes in client side, when trying to mix STDIN with socket reading in different threads. Note, I succeeded with using Tkx as workaround to STDIN. But my intention is to build short samples for teaching purposes only, in several programming languages. I intend to create the program minimal, with no UI, as simple as possible.
Here is the code of client, which has the problems:
use strict;
use IO::Socket::INET;
use threads;
our $sock = new IO::Socket::INET ( PeerAddr => 'localhost', PeerPort => 1234, Proto => 'tcp') or die "cannot connect to localhost";
my $thr = threads->create(\&msg_proc, $sock); #, $sock);
for (my $msg; $msg ne "exit";)
{
$msg = <STDIN>;
$msg =~ s/[\r\n\s\0]*\Z//g;
$sock->send ("$msg\n");# or die "can't send";
};
$sock->close();
print "exit main thread\n";
$thr->join() if $thr->is_running();
print "exit all\n";
sub msg_proc
{
my $svr = shift;
my $i = 0;
while ($svr)
{
sleep(1);
$svr->send ("{slept $i}\n") or die "server closed connection";
my $svr_msg = <$svr> or die "server closed connection";
$svr_msg =~ s/[\r\n\s\0]*\Z//g;
print "From server: <<$i $svr_msg>>\n";
$i++;
}
print "sock exit\n";
}
The problem starts when I remove the line $svr->send in the thread procedure msg_proc. In this case the client fails to read normally from STDIN, looks like interfering with socket reading operation <$svr>. Looks like it interferes with <STDIN> operation. For some reason these two can't coexist in parallel. Note, the C++ and Java versions of these demos do not have this problem.
This is the code of the server:
use strict;
use IO::Socket::INET;
use threads;
my $sock = IO::Socket::INET -> new (LocalPort => 1234, Proto => 'tcp', Listen => 1, Reuse => 1) or die "Could not create socket: $!\n";
print "server started\n";
my $i = 0;
while (my $s = $sock->accept())
{
print "New connection\n";
my $thr = threads->create(\&client_proc, $s, $i);
$s->send("welcome $i\n");
$i++;
}
sub client_proc
{
my $client = shift;
my $client_no = shift;
print "## client $client_no started\n";
$client->send("hello $client_no\n");
for (my $msg; $msg ne "exit";)
{
$msg = <$client> or die "client $client_no closed connection";
$msg =~ s/[\r\n\s\0]*\Z//;
print "From client $client_no: '$msg' len: ", length ($msg), "\n";
$client->send( "client $client_no: $msg\n" ) or die "client $client_no closed connection";
};
$client->close();
print "## client $i exit\n";
}
As I understand from here, the use of interpreter-based threads in perl is officially discouraged. But I can't understand, what interpreter-based threads actually means, and what is exactly the alternative provided. Does this mean using threads is discouraged in perl at all?
Note: I am using Strawberry Perl 5.32.1 64 bit under Windows 11, zip package, no msi. But under ActiveState Perl the problem was identically the same.