php server script: stream_select returning false

I am new to socket programming. the following snippet of code just keeps the server waiting. But If I remove line 22 (delete server socket), the server responds with all the code before line 22, but gives the stream_select error message and stops. I have copied this code as is from other online sources. Can anybody pls help.

while (true) {
// prepare readable sockets
$read_sockets = $client_sockets;
$read_sockets[] = $server;
// start reading and use a large timeout
if(false === stream_select($read_sockets, $write, $except, 300000)) {
die('stream_select error.');
}
// new client
if(in_array($server, $read_sockets)) {
    $new_client = stream_socket_accept($server);
    if ($new_client) {
        //print remote client information, ip and port number
        echo 'new connection: ' . stream_socket_get_name($new_client, true) 
        . "\n";
        $client_sockets[] = $new_client;
        echo "total clients: ". count($client_sockets) . "\n";
        //$output = "hello new client.\n";
        //fwrite($new_client, $output);
    }
    //delete the server socket from the read sockets
    //unset($read_sockets[ array_search($server, $read_sockets) ]);
}
// message from existing client
foreach ($read_sockets as $socket) {
    $data = fread($socket, 128);
    echo "data: " . $data . "\n";
    $tk103_data = explode( ',', $data);
    $response = ""; 
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