Using select to poll connections - TCP server - perl

Question

use strict; use warnings;
use IO::Socket;
use IO::Select;
my $read_select = IO::Select->new();
my $write_select = IO::Select->new();
my $socket = IO::Socket::INET->new(
LocalHost => '127.0.0.1',
LocalPort => '5556',
Proto => 'tcp',
Listen => 50,
Reuse => 1,
) or die "Could not create socket: $!";
print "Socket Created . Waiting for connection ...\n";
## poll to accept new connection or to receive data from a connection
$read_select->add($socket);
print "Added socket to read list ";
my $reade;
my $newconn;
my #read;
my #write;
while(1) {
#read = $read_select->can_read();
foreach my $reade(#read) {
if($reade == $socket) {
print "New conn received";
my $newconn = $reade->accept();
$write_select->add($newconn);
}
else {
print "data received";
}
}
}
#write = $write_select->can_write();
foreach my $write(#write) {
$write->send("got ur data");
}
I am trying to poll for connections using select statement. Why is that if i use an infinite loop, no connection is accepted. It works fine without while(1)

Answer 1

I think you are being bitten by I/O buffering here. Perl buffers all input and output. It generally doesn't print to the terminal until it has received an entire line.
Your code is probably working with the while(1), but you can't see the output of your debug print statements because the output to the terminal is being buffered. Once you get to the second time through the loop, $read_select->can_read() blocks forever, so you never see the output of the print statements.
You can probably fix this just by adding \n to the end of each print statement. Another option is setting $| = 1;. This disables buffering. See perlvar's discussion of $| for more information on buffering.