<?php

ignore_user_abort(true); /* try to change the value to true or false and see the difference */
set_time_limit(0);

for($i = 1; $i <= 30; ++$i)
{
    /* these 3 instructions are required to make the function ignore_user_abort/connection_status work */
    echo ' ';
    flush();
    ob_flush();

    file_put_contents('counter.txt', $i);
    sleep(1);
}