question about a simple incorrect gab client

[Jack Wu]

i'm reading Network Programming with Perl
there is an example in chapter5:concurrent clients.

#!/usr/bin/perl
use strict;
use IO::Socket qw(:DEFAULT :crlf);
 
my $host=shift or die"Usage:gabl.pl host [port]\n";
my $port=shift || 'tcp';
 
my $socket=IO::Socket::INET->new(PeerAddr=>$host,PeerPort=>$port) or die "can't connect:$!";
 
my($from_server,$from_user);
 
LOOP:
while(1){
        {
        local $/=CRLF;
        last LOOP unless $from_server=<$socket>;
        chomp $from_server;
        }
        print $from_server."\n";
 
        last unless $from_server=<>;
        chomp($from_user);
        print $socket $from_user,CRLF;
}
 

the author said if we change "last LOOP unless $from_server=<$socket>" into a loop like

while($from_server=<$socket>){
   chomp $from_server;
   print $from_server,"\n";}
 

this will cause a deadlock,this is what the author say
" Now the script hangs after it reads the first line from the server. The FTP server is waiting for us to send it a command, but the script is waiting for another line from the server and hasn't even yet asked us for input, a situation known as deadlock. "
I just don't understand why the script hangs after it reads the first line from the socket if the socket contains more than one line.

[numberwhun]

Well, as the author has stated, if the FTP server is waiting for a command to be issued and at the same time the server has noticed that it hasn't actually been asked for input, its a deadlock.