Hm. This seems to be a platform specific problem--which OS are you running?--because your code (with one minor change), works for me:

C:\test>perl 831580.pl 1234
enter port: 1234
socket OK
 bind OK
 listen OK
 Server started at 192.168.1.31:1234
Server ready. Waiting for connections...
got a connection from: 192.168.1.31:52479 IO::Socket::INET=GLOB(0x4d7c
+110)
list
connect to this server:
client: 192.168.1.31:52479  4
192.168.1.31:52479 fred
192.168.1.31:52479 bill
192.168.1.31:52479 test
192.168.1.31:52479 more
192.168.1.31:52479 still more
from 192.168.1.31:52479:
from 192.168.1.31:52479:
from 192.168.1.31:52479:
from 192.168.1.31:52479:
from 192.168.1.31:52479:
from 192.168.1.31:52479: hfrom 192.168.1.31:52479: efrom 192.168.1.31:
+52479: lfrom 192.168.1.31:52479: lfrom 192.168.1.31:52479: ofrom 192.
+168.1.31:52479:
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I had to change 1 line:

        while( my $tmp = <STDIN> ) { ##sysread(STDIN, $tmp, BUFSIZE) )
+ {
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because using sysread on STDIN means that no CRLF translation is done and so chomp doesn't do the right thing on my OS.

I strongly suspect that your thread is dying because you are calling die.

Try changing these two lines (remove the \n so that the line numbers are output), and then post your output:

                                open $client, "+<$fileno" || die "$!";
                                syswrite( $client, $msg_t ) || die ": 
+$!";
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